Proposal: Generic WAL logical messages

From c19d7274091baee4a523333b1fa0ac684ace4cc9 Mon Sep 17 00:00:00 2001
From: Petr Jelinek <pjmodos@pjmodos.net>
Date: Fri, 22 Jan 2016 20:15:22 +0100
Subject: [PATCH] Logical Messages

---
 contrib/test_decoding/Makefile                  |   2 +-
 contrib/test_decoding/test_decoding.c           |  22 +++-
 doc/src/sgml/func.sgml                          |  42 ++++++++
 doc/src/sgml/logicaldecoding.sgml               |  22 ++++
 src/backend/access/rmgrdesc/Makefile            |   4 +-
 src/backend/access/rmgrdesc/logicalmsgdesc.c    |  33 ++++++
 src/backend/access/transam/rmgr.c               |   1 +
 src/backend/replication/logical/Makefile        |   2 +-
 src/backend/replication/logical/decode.c        |  37 +++++++
 src/backend/replication/logical/logical.c       |  38 +++++++
 src/backend/replication/logical/logicalfuncs.c  |  27 +++++
 src/backend/replication/logical/message.c       | 132 ++++++++++++++++++++++++
 src/backend/replication/logical/reorderbuffer.c |  73 +++++++++++++
 src/bin/pg_xlogdump/rmgrdesc.c                  |   1 +
 src/include/access/rmgrlist.h                   |   1 +
 src/include/catalog/pg_proc.h                   |   4 +
 src/include/replication/logicalfuncs.h          |   2 +
 src/include/replication/message.h               |  42 ++++++++
 src/include/replication/output_plugin.h         |  13 +++
 src/include/replication/reorderbuffer.h         |  21 ++++
 20 files changed, 514 insertions(+), 5 deletions(-)
 create mode 100644 src/backend/access/rmgrdesc/logicalmsgdesc.c
 create mode 100644 src/backend/replication/logical/message.c
 create mode 100644 src/include/replication/message.h

diff --git a/contrib/test_decoding/Makefile b/contrib/test_decoding/Makefile
index a362e69..8fdcfbc 100644
--- a/contrib/test_decoding/Makefile
+++ b/contrib/test_decoding/Makefile
@@ -38,7 +38,7 @@ submake-test_decoding:
 	$(MAKE) -C $(top_builddir)/contrib/test_decoding
 
 REGRESSCHECKS=ddl rewrite toast permissions decoding_in_xact decoding_into_rel \
-	binary prepared replorigin
+	binary prepared replorigin messages
 
 regresscheck: | submake-regress submake-test_decoding temp-install
 	$(MKDIR_P) regression_output
diff --git a/contrib/test_decoding/test_decoding.c b/contrib/test_decoding/test_decoding.c
index 4cf808f..f655355 100644
--- a/contrib/test_decoding/test_decoding.c
+++ b/contrib/test_decoding/test_decoding.c
@@ -21,6 +21,7 @@
 
 #include "replication/output_plugin.h"
 #include "replication/logical.h"
+#include "replication/message.h"
 #include "replication/origin.h"
 
 #include "utils/builtins.h"
@@ -63,11 +64,15 @@ static void pg_decode_change(LogicalDecodingContext *ctx,
 				 ReorderBufferChange *change);
 static bool pg_decode_filter(LogicalDecodingContext *ctx,
 				 RepOriginId origin_id);
+static void pg_decode_message(LogicalDecodingContext *ctx,
+							  ReorderBufferTXN *txn, XLogRecPtr message_lsn,
+							  bool transactional, const char *prefix,
+							  Size sz, const char *message);
 
 void
 _PG_init(void)
 {
-	/* other plugins can perform things here */
+	RegisterLogicalMsgPrefix("test");
 }
 
 /* specify output plugin callbacks */
@@ -82,6 +87,7 @@ _PG_output_plugin_init(OutputPluginCallbacks *cb)
 	cb->commit_cb = pg_decode_commit_txn;
 	cb->filter_by_origin_cb = pg_decode_filter;
 	cb->shutdown_cb = pg_decode_shutdown;
+	cb->message_cb = pg_decode_message;
 }
 
 
@@ -471,3 +477,17 @@ pg_decode_change(LogicalDecodingContext *ctx, ReorderBufferTXN *txn,
 
 	OutputPluginWrite(ctx, true);
 }
+
+static void
+pg_decode_message(LogicalDecodingContext *ctx,
+				  ReorderBufferTXN *txn, XLogRecPtr lsn,
+				  bool transactional, const char *prefix,
+				  Size sz, const char *message)
+{
+	OutputPluginPrepareWrite(ctx, true);
+	appendStringInfo(ctx->out, "message: lsn: %X/%X transactional: %d prefix: %s, sz: %zu content:",
+					 (uint32)(lsn >> 32), (uint32)lsn, transactional, prefix,
+					 sz);
+	appendBinaryStringInfo(ctx->out, message, sz);
+	OutputPluginWrite(ctx, true);
+}
diff --git a/doc/src/sgml/func.sgml b/doc/src/sgml/func.sgml
index 4d2b88f..d55a2b1 100644
--- a/doc/src/sgml/func.sgml
+++ b/doc/src/sgml/func.sgml
@@ -17639,6 +17639,48 @@ postgres=# SELECT * FROM pg_xlogfile_name_offset(pg_stop_backup());
        </entry>
       </row>
 
+      <row>
+       <entry id="pg-logical-send-message-text">
+        <indexterm>
+         <primary>pg_logical_send_message</primary>
+        </indexterm>
+        <literal><function>pg_logical_send_message(<parameter>transactional</parameter> <type>bool</type>, <parameter>prefix</parameter> <type>text</type>, <parameter>content</parameter> <type>text</type>)</function></literal>
+       </entry>
+       <entry>
+        void
+       </entry>
+       <entry>
+        Write text logical decoding message. This can be used to pass generic
+        messages to logical decoding plugins through WAL. The parameter
+        <parameter>transactional</parameter> specifies if the message should
+        be part of current transaction or if it should be written and decoded
+        immediately. The <parameter>prefix</parameter> has to be prefix which
+        was registered by a plugin. The <parameter>content</parameter> is
+        content of the message.
+       </entry>
+      </row>
+
+      <row>
+       <entry id="pg-logical-send-message-bytea">
+        <indexterm>
+         <primary>pg_logical_send_message</primary>
+        </indexterm>
+        <literal><function>pg_logical_send_message(<parameter>transactional</parameter> <type>bool</type>, <parameter>prefix</parameter> <type>text</type>, <parameter>content</parameter> <type>bytea</type>)</function></literal>
+       </entry>
+       <entry>
+        void
+       </entry>
+       <entry>
+        Write binary logical decoding message. This can be used to pass generic
+        messages to logical decoding plugins through WAL. The parameter
+        <parameter>transactional</parameter> specifies if the message should
+        be part of current transaction or if it should be written and decoded
+        immediately. The <parameter>prefix</parameter> has to be prefix which
+        was registered by a plugin. The <parameter>content</parameter> is
+        content of the message.
+       </entry>
+      </row>
+
      </tbody>
     </tgroup>
    </table>
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 1ae5eb6..1d28de0 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -363,6 +363,7 @@ typedef struct OutputPluginCallbacks
     LogicalDecodeBeginCB begin_cb;
     LogicalDecodeChangeCB change_cb;
     LogicalDecodeCommitCB commit_cb;
+    LogicalDecodeMessageCB message_cb;
     LogicalDecodeFilterByOriginCB filter_by_origin_cb;
     LogicalDecodeShutdownCB shutdown_cb;
 } OutputPluginCallbacks;
@@ -602,6 +603,27 @@ typedef bool (*LogicalDecodeFilterByOriginCB) (
        more efficient.
      </para>
      </sect3>
+
+    <sect3 id="logicaldecoding-output-plugin-message">
+     <title>Generic Message Callback</title>
+
+     <para>
+      The optional <function>message_cb</function> callback is called whenever
+      a logical decoding message has been decoded.
+<programlisting>
+typedef void (*LogicalDecodeMessageCB) (
+    struct LogicalDecodingContext *,
+    ReorderBufferTXN *txn,
+    XLogRecPtr message_lsn,
+    bool transactional,
+    const char *prefix,
+    Size message_size,
+    const char *message
+);
+</programlisting>
+     </para>
+    </sect3>
+
    </sect2>
 
    <sect2 id="logicaldecoding-output-plugin-output">
diff --git a/src/backend/access/rmgrdesc/Makefile b/src/backend/access/rmgrdesc/Makefile
index c72a1f2..723b4d8 100644
--- a/src/backend/access/rmgrdesc/Makefile
+++ b/src/backend/access/rmgrdesc/Makefile
@@ -9,8 +9,8 @@ top_builddir = ../../../..
 include $(top_builddir)/src/Makefile.global
 
 OBJS = brindesc.o clogdesc.o committsdesc.o dbasedesc.o gindesc.o gistdesc.o \
-	   hashdesc.o heapdesc.o mxactdesc.o nbtdesc.o relmapdesc.o \
-	   replorigindesc.o seqdesc.o smgrdesc.o spgdesc.o \
+	   hashdesc.o heapdesc.o logicalmsgdesc.o mxactdesc.o nbtdesc.o \
+	   relmapdesc.o replorigindesc.o seqdesc.o smgrdesc.o spgdesc.o \
 	   standbydesc.o tblspcdesc.o xactdesc.o xlogdesc.o
 
 include $(top_srcdir)/src/backend/common.mk
diff --git a/src/backend/access/rmgrdesc/logicalmsgdesc.c b/src/backend/access/rmgrdesc/logicalmsgdesc.c
new file mode 100644
index 0000000..739ee10
--- /dev/null
+++ b/src/backend/access/rmgrdesc/logicalmsgdesc.c
@@ -0,0 +1,33 @@
+/*-------------------------------------------------------------------------
+ *
+ * logicalmsgdesc.c
+ *	  rmgr descriptor routines for replication/logical/message.c
+ *
+ * Portions Copyright (c) 2015-2016, PostgreSQL Global Development Group
+ *
+ *
+ * IDENTIFICATION
+ *	  src/backend/access/rmgrdesc/logicalmsgdesc.c
+ *
+ *-------------------------------------------------------------------------
+ */
+#include "postgres.h"
+
+#include "replication/message.h"
+
+void
+logicalmsg_desc(StringInfo buf, XLogReaderState *record)
+{
+	char			   *rec = XLogRecGetData(record);
+	xl_logical_message *xlrec = (xl_logical_message *) rec;
+
+	appendStringInfo(buf, "%s message size %zu bytes",
+					 xlrec->transactional ? "transactional" : "nontransactional",
+					 xlrec->message_size);
+}
+
+const char *
+logicalmsg_identify(uint8 info)
+{
+	return NULL;
+}
diff --git a/src/backend/access/transam/rmgr.c b/src/backend/access/transam/rmgr.c
index 7c4d773..1a42121 100644
--- a/src/backend/access/transam/rmgr.c
+++ b/src/backend/access/transam/rmgr.c
@@ -23,6 +23,7 @@
 #include "commands/dbcommands_xlog.h"
 #include "commands/sequence.h"
 #include "commands/tablespace.h"
+#include "replication/message.h"
 #include "replication/origin.h"
 #include "storage/standby.h"
 #include "utils/relmapper.h"
diff --git a/src/backend/replication/logical/Makefile b/src/backend/replication/logical/Makefile
index 8adea13..1d7ca06 100644
--- a/src/backend/replication/logical/Makefile
+++ b/src/backend/replication/logical/Makefile
@@ -14,7 +14,7 @@ include $(top_builddir)/src/Makefile.global
 
 override CPPFLAGS := -I$(srcdir) $(CPPFLAGS)
 
-OBJS = decode.o logical.o logicalfuncs.o reorderbuffer.o origin.o \
+OBJS = decode.o logical.o logicalfuncs.o message.o origin.o reorderbuffer.o \
 	snapbuild.o
 
 include $(top_srcdir)/src/backend/common.mk
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index 88c3a49..110f958 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -39,6 +39,7 @@
 
 #include "replication/decode.h"
 #include "replication/logical.h"
+#include "replication/message.h"
 #include "replication/reorderbuffer.h"
 #include "replication/origin.h"
 #include "replication/snapbuild.h"
@@ -58,6 +59,7 @@ static void DecodeHeapOp(LogicalDecodingContext *ctx, XLogRecordBuffer *buf);
 static void DecodeHeap2Op(LogicalDecodingContext *ctx, XLogRecordBuffer *buf);
 static void DecodeXactOp(LogicalDecodingContext *ctx, XLogRecordBuffer *buf);
 static void DecodeStandbyOp(LogicalDecodingContext *ctx, XLogRecordBuffer *buf);
+static void DecodeLogicalMsgOp(LogicalDecodingContext *ctx, XLogRecordBuffer *buf);
 
 /* individual record(group)'s handlers */
 static void DecodeInsert(LogicalDecodingContext *ctx, XLogRecordBuffer *buf);
@@ -115,6 +117,10 @@ LogicalDecodingProcessRecord(LogicalDecodingContext *ctx, XLogReaderState *recor
 			DecodeHeapOp(ctx, &buf);
 			break;
 
+		case RM_LOGICALMSG_ID:
+			DecodeLogicalMsgOp(ctx, &buf);
+			break;
+
 			/*
 			 * Rmgrs irrelevant for logical decoding; they describe stuff not
 			 * represented in logical decoding. Add new rmgrs in rmgrlist.h's
@@ -431,6 +437,37 @@ DecodeHeapOp(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
 	}
 }
 
+/*
+ * Handle rmgr LOGICALMSG_ID records for DecodeRecordIntoReorderBuffer().
+ */
+static void
+DecodeLogicalMsgOp(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
+{
+	SnapBuild  *builder = ctx->snapshot_builder;
+	XLogReaderState *r = buf->record;
+	uint8		info = XLogRecGetInfo(r) & ~XLR_INFO_MASK;
+	xl_logical_message *message;
+
+	if (info != XLOG_LOGICAL_MESSAGE)
+		elog(ERROR, "unexpected RM_LOGICALMSG_ID record type: %u", info);
+
+	message = (xl_logical_message *) XLogRecGetData(r);
+
+	if (message->transactional &&
+		!SnapBuildProcessChange(builder, XLogRecGetXid(r), buf->origptr))
+		return;
+	else if(!message->transactional &&
+			(SnapBuildCurrentState(ctx->snapshot_builder) != SNAPBUILD_CONSISTENT ||
+			 SnapBuildXactNeedsSkip(builder, buf->origptr)))
+		return;
+
+	ReorderBufferQueueMessage(ctx->reorder, XLogRecGetXid(r),
+							  buf->endptr, message->transactional,
+							  message->message, /* first part of message is prefix */
+							  message->message_size,
+							  message->message + message->prefix_size);
+}
+
 static inline bool
 FilterByOrigin(LogicalDecodingContext *ctx, RepOriginId origin_id)
 {
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index 2e6d3f9..998fb79 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -62,6 +62,9 @@ static void commit_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
 				  XLogRecPtr commit_lsn);
 static void change_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
 				  Relation relation, ReorderBufferChange *change);
+static void message_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
+				  XLogRecPtr message_lsn, bool transactional,
+				  const char *prefix, Size sz, const char *message);
 
 static void LoadOutputPlugin(OutputPluginCallbacks *callbacks, char *plugin);
 
@@ -178,6 +181,7 @@ StartupDecodingContext(List *output_plugin_options,
 	ctx->reorder->begin = begin_cb_wrapper;
 	ctx->reorder->apply_change = change_cb_wrapper;
 	ctx->reorder->commit = commit_cb_wrapper;
+	ctx->reorder->message = message_cb_wrapper;
 
 	ctx->out = makeStringInfo();
 	ctx->prepare_write = prepare_write;
@@ -702,6 +706,40 @@ filter_by_origin_cb_wrapper(LogicalDecodingContext *ctx, RepOriginId origin_id)
 	return ret;
 }
 
+static void message_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
+							   XLogRecPtr message_lsn,
+							   bool transactional, const char *prefix,
+							   Size sz, const char *message)
+{
+	LogicalDecodingContext *ctx = cache->private_data;
+	LogicalErrorCallbackState state;
+	ErrorContextCallback errcallback;
+
+	if (ctx->callbacks.message_cb == NULL)
+		return;
+
+	/* Push callback + info on the error context stack */
+	state.ctx = ctx;
+	state.callback_name = "message";
+	state.report_location = message_lsn; /* beginning of commit record */
+	errcallback.callback = output_plugin_error_callback;
+	errcallback.arg = (void *) &state;
+	errcallback.previous = error_context_stack;
+	error_context_stack = &errcallback;
+
+	/* set output state */
+	ctx->accept_writes = true;
+	ctx->write_xid = txn != NULL ? txn->xid : InvalidTransactionId;
+	ctx->write_location = message_lsn;
+
+	/* do the actual work: call callback */
+	ctx->callbacks.message_cb(ctx, txn, message_lsn, transactional,
+							  prefix, sz, message);
+
+	/* Pop the error context stack */
+	error_context_stack = errcallback.previous;
+}
+
 /*
  * Set the required catalog xmin horizon for historic snapshots in the current
  * replication slot.
diff --git a/src/backend/replication/logical/logicalfuncs.c b/src/backend/replication/logical/logicalfuncs.c
index f789fc1..2eb26d4 100644
--- a/src/backend/replication/logical/logicalfuncs.c
+++ b/src/backend/replication/logical/logicalfuncs.c
@@ -24,6 +24,8 @@
 #include "access/xlog_internal.h"
 #include "access/xlogutils.h"
 
+#include "access/xact.h"
+
 #include "catalog/pg_type.h"
 
 #include "nodes/makefuncs.h"
@@ -41,6 +43,7 @@
 #include "replication/decode.h"
 #include "replication/logical.h"
 #include "replication/logicalfuncs.h"
+#include "replication/message.h"
 
 #include "storage/fd.h"
 
@@ -363,3 +366,27 @@ pg_logical_slot_peek_binary_changes(PG_FUNCTION_ARGS)
 {
 	return pg_logical_slot_get_changes_guts(fcinfo, false, true);
 }
+
+
+/*
+ * SQL function returning the changestream in binary, only peeking ahead.
+ */
+Datum
+pg_logical_send_message_bytea(PG_FUNCTION_ARGS)
+{
+	bool		transactional = PG_GETARG_BOOL(0);
+	char	   *prefix = text_to_cstring(PG_GETARG_TEXT_PP(1));
+	bytea	   *data = PG_GETARG_BYTEA_PP(2);
+	XLogRecPtr	lsn;
+
+	lsn = LogLogicalMessage(prefix, VARDATA_ANY(data), VARSIZE_ANY_EXHDR(data),
+							transactional);
+	PG_RETURN_LSN(lsn);
+}
+
+Datum
+pg_logical_send_message_text(PG_FUNCTION_ARGS)
+{
+	/* bytea and text are compatible */
+	return pg_logical_send_message_bytea(fcinfo);
+}
diff --git a/src/backend/replication/logical/message.c b/src/backend/replication/logical/message.c
new file mode 100644
index 0000000..e5f4feb
--- /dev/null
+++ b/src/backend/replication/logical/message.c
@@ -0,0 +1,132 @@
+/*-------------------------------------------------------------------------
+ *
+ * message.c
+ *	  Generic logical messages.
+ *
+ * Copyright (c) 2013-2016, PostgreSQL Global Development Group
+ *
+ * IDENTIFICATION
+ *	  src/backend/replication/logical/message.c
+ *
+ * NOTES
+ *
+ * Generic logical messages allow XLOG logging of arbitrary binary blobs that
+ * get passed to the logical decoding plugin. In normal XLOG processing they
+ * are same as NOOP.
+ *
+ * These messages can be either transactional or non-transactional.
+ * Transactional messages are part of current transaction and will be sent to
+ * decoding plugin using in a same way as DML operations.
+ * Non-transactional messages are sent to the plugin at the time when the
+ * logical decoding reads them from XLOG.
+ *
+ * Every message carries prefix to avoid conflicts between different decoding
+ * plugins. The prefix has to be registered before the message using that
+ * prefix can be written to XLOG. The prefix can be registered exactly once to
+ * avoid situation where multiple third party extensions try to use same
+ * prefix.
+ *
+ * ---------------------------------------------------------------------------
+ */
+
+#include "postgres.h"
+
+#include "access/xact.h"
+
+#include "catalog/indexing.h"
+
+#include "nodes/execnodes.h"
+
+#include "replication/message.h"
+#include "replication/logical.h"
+
+#include "utils/memutils.h"
+
+/* List of registered logical message prefixes. */
+static List	   *LogicalMsgPrefixList = NIL;
+
+XLogRecPtr
+LogLogicalMessage(const char *prefix, const char *message, size_t size,
+				  bool transactional)
+{
+	ListCell		   *lc;
+	bool				found = false;
+	xl_logical_message	xlrec;
+
+	/* Check if the provided prefix is known to us. */
+	foreach(lc, LogicalMsgPrefixList)
+	{
+		char	*mp = lfirst(lc);
+
+		if (strcmp(prefix, mp) == 0)
+		{
+			found = true;
+			break;
+		}
+	}
+	if (!found)
+		ereport(ERROR,
+				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+				 errmsg("standby message prefix \"%s\" is not registered",
+						prefix)));
+
+	/*
+	 * Force xid to be allocated if we're sending a transactional message.
+	 */
+	if (transactional)
+	{
+		Assert(IsTransactionState());
+		GetCurrentTransactionId();
+	}
+
+	xlrec.transactional = transactional;
+	xlrec.prefix_size = strlen(prefix) + 1;
+	xlrec.message_size = size;
+
+	XLogBeginInsert();
+	XLogRegisterData((char *) &xlrec, SizeOfLogicalMessage);
+	XLogRegisterData((char *) prefix, xlrec.prefix_size);
+	XLogRegisterData((char *) message, size);
+
+	return XLogInsert(RM_LOGICALMSG_ID, XLOG_LOGICAL_MESSAGE);
+}
+
+void
+RegisterLogicalMsgPrefix(const char *prefix)
+{
+	ListCell	   *lc;
+	bool			found = false;
+	MemoryContext	oldcxt;
+
+	/* Check for duplicit registrations. */
+	foreach(lc, LogicalMsgPrefixList)
+	{
+		char	*mp = lfirst(lc);
+
+		if (strcmp(prefix, mp) == 0)
+		{
+			found = true;
+			break;
+		}
+	}
+	if (found)
+		ereport(ERROR,
+				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+				 errmsg("logical decoding message prefix \"%s\" is already registered",
+						prefix)));
+
+	oldcxt = MemoryContextSwitchTo(TopMemoryContext);
+	LogicalMsgPrefixList = lappend(LogicalMsgPrefixList, pstrdup(prefix));
+	MemoryContextSwitchTo(oldcxt);
+}
+
+void
+logicalmsg_redo(XLogReaderState *record)
+{
+	uint8		info = XLogRecGetInfo(record) & ~XLR_INFO_MASK;
+
+	if (info != XLOG_LOGICAL_MESSAGE)
+			elog(PANIC, "logicalmsg_redo: unknown op code %u", info);
+
+	/* This is only interesting for logical decoding, see decode.c. */
+}
diff --git a/src/backend/replication/logical/reorderbuffer.c b/src/backend/replication/logical/reorderbuffer.c
index 78acced..99e9ec7 100644
--- a/src/backend/replication/logical/reorderbuffer.c
+++ b/src/backend/replication/logical/reorderbuffer.c
@@ -414,6 +414,11 @@ ReorderBufferReturnChange(ReorderBuffer *rb, ReorderBufferChange *change)
 				change->data.tp.oldtuple = NULL;
 			}
 			break;
+		case REORDER_BUFFER_CHANGE_MESSAGE:
+			if (change->data.msg.message != NULL)
+				pfree(change->data.msg.message);
+			change->data.msg.message = NULL;
+			break;
 		case REORDER_BUFFER_CHANGE_INTERNAL_SNAPSHOT:
 			if (change->data.snapshot)
 			{
@@ -599,6 +604,39 @@ ReorderBufferQueueChange(ReorderBuffer *rb, TransactionId xid, XLogRecPtr lsn,
 	ReorderBufferCheckSerializeTXN(rb, txn);
 }
 
+void
+ReorderBufferQueueMessage(ReorderBuffer *rb, TransactionId xid, XLogRecPtr lsn,
+						  bool transactional, const char *prefix, Size msg_sz,
+						  const char *msg)
+{
+	ReorderBufferTXN *txn = NULL;
+
+	if (transactional)
+	{
+		ReorderBufferChange *change;
+
+		txn = ReorderBufferTXNByXid(rb, xid, true, NULL, lsn, true);
+
+		Assert(xid != InvalidTransactionId);
+		Assert(txn != NULL);
+
+		change = ReorderBufferGetChange(rb);
+		change->action = REORDER_BUFFER_CHANGE_MESSAGE;
+		change->data.msg.transactional = true;
+		change->data.msg.prefix = pstrdup(prefix);
+		change->data.msg.message_size = msg_sz;
+		change->data.msg.message = palloc(msg_sz);
+		memcpy(change->data.msg.message, msg, msg_sz);
+
+		ReorderBufferQueueChange(rb, xid, lsn, change);
+	}
+	else
+	{
+		rb->message(rb, txn, lsn, transactional, prefix, msg_sz, msg);
+	}
+}
+
+
 static void
 AssertTXNLsnOrder(ReorderBuffer *rb)
 {
@@ -1465,6 +1503,14 @@ ReorderBufferCommit(ReorderBuffer *rb, TransactionId xid,
 					specinsert = change;
 					break;
 
+				case REORDER_BUFFER_CHANGE_MESSAGE:
+					rb->message(rb, txn, change->lsn,
+								change->data.msg.transactional,
+								change->data.msg.prefix,
+								change->data.msg.message_size,
+								change->data.msg.message);
+					break;
+
 				case REORDER_BUFFER_CHANGE_INTERNAL_SNAPSHOT:
 					/* get rid of the old */
 					TeardownHistoricSnapshot(false);
@@ -2117,6 +2163,21 @@ ReorderBufferSerializeChange(ReorderBuffer *rb, ReorderBufferTXN *txn,
 				}
 				break;
 			}
+		case REORDER_BUFFER_CHANGE_MESSAGE:
+			{
+				char	   *data;
+				size_t		prefix_size = strlen(change->data.msg.prefix) + 1;
+
+				sz += prefix_size + change->data.msg.message_size;
+				ReorderBufferSerializeReserve(rb, sz);
+
+				data = ((char *) rb->outbuf) + sizeof(ReorderBufferDiskChange);
+				memcpy(data, change->data.msg.prefix,
+					   prefix_size);
+				memcpy(data + prefix_size, change->data.msg.message,
+					   change->data.msg.message_size);
+				break;
+			}
 		case REORDER_BUFFER_CHANGE_INTERNAL_SNAPSHOT:
 			{
 				Snapshot	snap;
@@ -2354,6 +2415,18 @@ ReorderBufferRestoreChange(ReorderBuffer *rb, ReorderBufferTXN *txn,
 				data += len;
 			}
 			break;
+		case REORDER_BUFFER_CHANGE_MESSAGE:
+			{
+				Size		message_size = change->data.msg.message_size;
+				Size		prefix_size = strlen(data) + 1;
+
+				change->data.msg.prefix = pstrdup(data);
+				change->data.msg.message = palloc(message_size);
+				memcpy(change->data.msg.message, data + prefix_size,
+					   message_size);
+
+				data += prefix_size + message_size;
+			}
 		case REORDER_BUFFER_CHANGE_INTERNAL_SNAPSHOT:
 			{
 				Snapshot	oldsnap;
diff --git a/src/bin/pg_xlogdump/rmgrdesc.c b/src/bin/pg_xlogdump/rmgrdesc.c
index f9cd395..6ba7f22 100644
--- a/src/bin/pg_xlogdump/rmgrdesc.c
+++ b/src/bin/pg_xlogdump/rmgrdesc.c
@@ -25,6 +25,7 @@
 #include "commands/dbcommands_xlog.h"
 #include "commands/sequence.h"
 #include "commands/tablespace.h"
+#include "replication/message.h"
 #include "replication/origin.h"
 #include "rmgrdesc.h"
 #include "storage/standbydefs.h"
diff --git a/src/include/access/rmgrlist.h b/src/include/access/rmgrlist.h
index fab912d..35c242d 100644
--- a/src/include/access/rmgrlist.h
+++ b/src/include/access/rmgrlist.h
@@ -45,3 +45,4 @@ PG_RMGR(RM_SPGIST_ID, "SPGist", spg_redo, spg_desc, spg_identify, spg_xlog_start
 PG_RMGR(RM_BRIN_ID, "BRIN", brin_redo, brin_desc, brin_identify, NULL, NULL)
 PG_RMGR(RM_COMMIT_TS_ID, "CommitTs", commit_ts_redo, commit_ts_desc, commit_ts_identify, NULL, NULL)
 PG_RMGR(RM_REPLORIGIN_ID, "ReplicationOrigin", replorigin_redo, replorigin_desc, replorigin_identify, NULL, NULL)
+PG_RMGR(RM_LOGICALMSG_ID, "LogicalMessage", logicalmsg_redo, logicalmsg_desc, logicalmsg_identify, NULL, NULL)
diff --git a/src/include/catalog/pg_proc.h b/src/include/catalog/pg_proc.h
index 244aa4d..8da6fae 100644
--- a/src/include/catalog/pg_proc.h
+++ b/src/include/catalog/pg_proc.h
@@ -5066,6 +5066,10 @@ DATA(insert OID = 3784 (  pg_logical_slot_peek_changes PGNSP PGUID 12 1000 1000
 DESCR("peek at changes from replication slot");
 DATA(insert OID = 3785 (  pg_logical_slot_peek_binary_changes PGNSP PGUID 12 1000 1000 25 0 f f f f f t v u 4 0 2249 "19 3220 23 1009" "{19,3220,23,1009,3220,28,17}" "{i,i,i,v,o,o,o}" "{slot_name,upto_lsn,upto_nchanges,options,location,xid,data}" _null_ _null_ pg_logical_slot_peek_binary_changes _null_ _null_ _null_ ));
 DESCR("peek at binary changes from replication slot");
+DATA(insert OID = 3577 (  pg_logical_send_message PGNSP PGUID 12 1 0 0 0 f f f f f f v u 3 0 3220 "16 25 25" _null_ _null_ _null_ _null_ _null_ pg_logical_send_message_text _null_ _null_ _null_ ));
+DESCR("send a textual message");
+DATA(insert OID = 3578 (  pg_logical_send_message PGNSP PGUID 12 1 0 0 0 f f f f f f v u 3 0 3220 "16 25 17" _null_ _null_ _null_ _null_ _null_ pg_logical_send_message_bytea _null_ _null_ _null_ ));
+DESCR("send a binary message");
 
 /* event triggers */
 DATA(insert OID = 3566 (  pg_event_trigger_dropped_objects		PGNSP PGUID 12 10 100 0 0 f f f f t t s s 0 0 2249 "" "{26,26,23,16,16,16,25,25,25,25,1009,1009}" "{o,o,o,o,o,o,o,o,o,o,o,o}" "{classid, objid, objsubid, original, normal, is_temporary, object_type, schema_name, object_name, object_identity, address_names, address_args}" _null_ _null_ pg_event_trigger_dropped_objects _null_ _null_ _null_ ));
diff --git a/src/include/replication/logicalfuncs.h b/src/include/replication/logicalfuncs.h
index c87a1df..cd3373e 100644
--- a/src/include/replication/logicalfuncs.h
+++ b/src/include/replication/logicalfuncs.h
@@ -21,4 +21,6 @@ extern Datum pg_logical_slot_get_binary_changes(PG_FUNCTION_ARGS);
 extern Datum pg_logical_slot_peek_changes(PG_FUNCTION_ARGS);
 extern Datum pg_logical_slot_peek_binary_changes(PG_FUNCTION_ARGS);
 
+extern Datum pg_logical_send_message_bytea(PG_FUNCTION_ARGS);
+extern Datum pg_logical_send_message_text(PG_FUNCTION_ARGS);
 #endif
diff --git a/src/include/replication/message.h b/src/include/replication/message.h
new file mode 100644
index 0000000..e4223f4
--- /dev/null
+++ b/src/include/replication/message.h
@@ -0,0 +1,42 @@
+/*-------------------------------------------------------------------------
+ * message.h
+ *	   Exports from replication/logical/message.c
+ *
+ * Copyright (c) 2013-2016, PostgreSQL Global Development Group
+ *
+ * src/include/replication/message.h
+ *-------------------------------------------------------------------------
+ */
+#ifndef PG_LOGICAL_MESSAGE_H
+#define PG_LOGICAL_MESSAGE_H
+
+#include "access/xlog.h"
+#include "access/xlogdefs.h"
+#include "access/xlogreader.h"
+
+/*
+ * Generic logical decoding message wal record.
+ */
+typedef struct xl_logical_message
+{
+	bool		transactional;					/* is message transactional? */
+	size_t		prefix_size;					/* length of prefix */
+	size_t		message_size;					/* size of the message */
+	char		message[FLEXIBLE_ARRAY_MEMBER];	/* message including the null
+												 * terminated prefx of length
+												 * prefix_size */
+} xl_logical_message;
+
+#define SizeOfLogicalMessage	(offsetof(xl_logical_message, message))
+
+extern XLogRecPtr LogLogicalMessage(const char *prefix, const char *message,
+									size_t size, bool transactional);
+extern void RegisterLogicalMsgPrefix(const char *prefix);
+
+/* RMGR API*/
+#define XLOG_LOGICAL_MESSAGE	0x00
+void		logicalmsg_redo(XLogReaderState *record);
+void		logicalmsg_desc(StringInfo buf, XLogReaderState *record);
+const char *logicalmsg_identify(uint8 info);
+
+#endif   /* PG_LOGICAL_MESSAGE_H */
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 577b12e..3a2ca98 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -74,6 +74,18 @@ typedef void (*LogicalDecodeCommitCB) (
 												   XLogRecPtr commit_lsn);
 
 /*
+ * Called for the generic logical decoding messages.
+ */
+typedef void (*LogicalDecodeMessageCB) (
+											 struct LogicalDecodingContext *,
+											 ReorderBufferTXN *txn,
+											 XLogRecPtr message_lsn,
+											 bool transactional,
+											 const char *prefix,
+											 Size message_size,
+											 const char *message);
+
+/*
  * Filter changes by origin.
  */
 typedef bool (*LogicalDecodeFilterByOriginCB) (
@@ -96,6 +108,7 @@ typedef struct OutputPluginCallbacks
 	LogicalDecodeBeginCB begin_cb;
 	LogicalDecodeChangeCB change_cb;
 	LogicalDecodeCommitCB commit_cb;
+	LogicalDecodeMessageCB message_cb;
 	LogicalDecodeFilterByOriginCB filter_by_origin_cb;
 	LogicalDecodeShutdownCB shutdown_cb;
 } OutputPluginCallbacks;
diff --git a/src/include/replication/reorderbuffer.h b/src/include/replication/reorderbuffer.h
index 2abee0a..f51f5c1 100644
--- a/src/include/replication/reorderbuffer.h
+++ b/src/include/replication/reorderbuffer.h
@@ -51,6 +51,7 @@ enum ReorderBufferChangeType
 	REORDER_BUFFER_CHANGE_INSERT,
 	REORDER_BUFFER_CHANGE_UPDATE,
 	REORDER_BUFFER_CHANGE_DELETE,
+	REORDER_BUFFER_CHANGE_MESSAGE,
 	REORDER_BUFFER_CHANGE_INTERNAL_SNAPSHOT,
 	REORDER_BUFFER_CHANGE_INTERNAL_COMMAND_ID,
 	REORDER_BUFFER_CHANGE_INTERNAL_TUPLECID,
@@ -95,6 +96,14 @@ typedef struct ReorderBufferChange
 			ReorderBufferTupleBuf *newtuple;
 		}			tp;
 
+		struct
+		{
+			bool transactional;
+			char *prefix;
+			size_t message_size;
+			char *message;
+		} msg;
+
 		/* New snapshot, set when action == *_INTERNAL_SNAPSHOT */
 		Snapshot	snapshot;
 
@@ -271,6 +280,15 @@ typedef void (*ReorderBufferCommitCB) (
 												   ReorderBufferTXN *txn,
 												   XLogRecPtr commit_lsn);
 
+/* message callback signature */
+typedef void (*ReorderBufferMessageCB) (
+												   ReorderBuffer *rb,
+												   ReorderBufferTXN *txn,
+												   XLogRecPtr message_lsn,
+												   bool transactional,
+												   const char *prefix, Size sz,
+												   const char *message);
+
 struct ReorderBuffer
 {
 	/*
@@ -297,6 +315,7 @@ struct ReorderBuffer
 	ReorderBufferBeginCB begin;
 	ReorderBufferApplyChangeCB apply_change;
 	ReorderBufferCommitCB commit;
+	ReorderBufferMessageCB message;
 
 	/*
 	 * Pointer that will be passed untouched to the callbacks.
@@ -347,6 +366,8 @@ ReorderBufferChange *ReorderBufferGetChange(ReorderBuffer *);
 void		ReorderBufferReturnChange(ReorderBuffer *, ReorderBufferChange *);
 
 void		ReorderBufferQueueChange(ReorderBuffer *, TransactionId, XLogRecPtr lsn, ReorderBufferChange *);
+void		ReorderBufferQueueMessage(ReorderBuffer *, TransactionId, XLogRecPtr lsn,
+									  bool transactional, const char *prefix, Size msg_sz, const char *msg);
 void ReorderBufferCommit(ReorderBuffer *, TransactionId,
 					XLogRecPtr commit_lsn, XLogRecPtr end_lsn,
 	  TimestampTz commit_time, RepOriginId origin_id, XLogRecPtr origin_lsn);
-- 
1.9.1

From 55a771c4770b73b5bedac7cd91bd0a50b0d6da45 Mon Sep 17 00:00:00 2001
From: Petr Jelinek <pjmodos@pjmodos.net>
Date: Wed, 24 Feb 2016 17:02:36 +0100
Subject: [PATCH] Logical Decoding Messages

---
 contrib/test_decoding/Makefile                  |   2 +-
 contrib/test_decoding/expected/messages.out     |  56 ++++++++++
 contrib/test_decoding/sql/messages.sql          |  17 +++
 contrib/test_decoding/test_decoding.c           |  22 +++-
 doc/src/sgml/func.sgml                          |  42 ++++++++
 doc/src/sgml/logicaldecoding.sgml               |  22 ++++
 src/backend/access/rmgrdesc/Makefile            |   4 +-
 src/backend/access/rmgrdesc/logicalmsgdesc.c    |  33 ++++++
 src/backend/access/transam/rmgr.c               |   1 +
 src/backend/replication/logical/Makefile        |   2 +-
 src/backend/replication/logical/decode.c        |  37 +++++++
 src/backend/replication/logical/logical.c       |  38 +++++++
 src/backend/replication/logical/logicalfuncs.c  |  27 +++++
 src/backend/replication/logical/message.c       | 132 ++++++++++++++++++++++++
 src/backend/replication/logical/reorderbuffer.c |  73 +++++++++++++
 src/bin/pg_xlogdump/rmgrdesc.c                  |   1 +
 src/include/access/rmgrlist.h                   |   1 +
 src/include/catalog/pg_proc.h                   |   4 +
 src/include/replication/logicalfuncs.h          |   2 +
 src/include/replication/message.h               |  42 ++++++++
 src/include/replication/output_plugin.h         |  13 +++
 src/include/replication/reorderbuffer.h         |  21 ++++
 22 files changed, 587 insertions(+), 5 deletions(-)
 create mode 100644 contrib/test_decoding/expected/messages.out
 create mode 100644 contrib/test_decoding/sql/messages.sql
 create mode 100644 src/backend/access/rmgrdesc/logicalmsgdesc.c
 create mode 100644 src/backend/replication/logical/message.c
 create mode 100644 src/include/replication/message.h

diff --git a/contrib/test_decoding/Makefile b/contrib/test_decoding/Makefile
index a362e69..8fdcfbc 100644
--- a/contrib/test_decoding/Makefile
+++ b/contrib/test_decoding/Makefile
@@ -38,7 +38,7 @@ submake-test_decoding:
 	$(MAKE) -C $(top_builddir)/contrib/test_decoding
 
 REGRESSCHECKS=ddl rewrite toast permissions decoding_in_xact decoding_into_rel \
-	binary prepared replorigin
+	binary prepared replorigin messages
 
 regresscheck: | submake-regress submake-test_decoding temp-install
 	$(MKDIR_P) regression_output
diff --git a/contrib/test_decoding/expected/messages.out b/contrib/test_decoding/expected/messages.out
new file mode 100644
index 0000000..d256851
--- /dev/null
+++ b/contrib/test_decoding/expected/messages.out
@@ -0,0 +1,56 @@
+-- predictability
+SET synchronous_commit = on;
+SELECT 'init' FROM pg_create_logical_replication_slot('regression_slot', 'test_decoding');
+ ?column? 
+----------
+ init
+(1 row)
+
+SELECT 'msg1' FROM pg_logical_send_message(true, 'test', 'msg1');
+ ?column? 
+----------
+ msg1
+(1 row)
+
+SELECT 'msg2' FROM pg_logical_send_message(false, 'test', 'msg2');
+ ?column? 
+----------
+ msg2
+(1 row)
+
+BEGIN;
+SELECT 'msg3' FROM pg_logical_send_message(true, 'test', 'msg3');
+ ?column? 
+----------
+ msg3
+(1 row)
+
+SELECT 'msg4' FROM pg_logical_send_message(false, 'test', 'msg4');
+ ?column? 
+----------
+ msg4
+(1 row)
+
+SELECT 'msg5' FROM pg_logical_send_message(true, 'test', 'msg5');
+ ?column? 
+----------
+ msg5
+(1 row)
+
+COMMIT;
+SELECT regexp_replace(data, 'lsn: [^ ]+', '') FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'force-binary', '0', 'skip-empty-xacts', '1');
+                       regexp_replace                        
+-------------------------------------------------------------
+ message:  transactional: 1 prefix: test, sz: 4 content:msg1
+ message:  transactional: 0 prefix: test, sz: 4 content:msg2
+ message:  transactional: 0 prefix: test, sz: 4 content:msg4
+ message:  transactional: 1 prefix: test, sz: 4 content:msg3
+ message:  transactional: 1 prefix: test, sz: 4 content:msg5
+(5 rows)
+
+SELECT 'init' FROM pg_drop_replication_slot('regression_slot');
+ ?column? 
+----------
+ init
+(1 row)
+
diff --git a/contrib/test_decoding/sql/messages.sql b/contrib/test_decoding/sql/messages.sql
new file mode 100644
index 0000000..7f462b8
--- /dev/null
+++ b/contrib/test_decoding/sql/messages.sql
@@ -0,0 +1,17 @@
+-- predictability
+SET synchronous_commit = on;
+
+SELECT 'init' FROM pg_create_logical_replication_slot('regression_slot', 'test_decoding');
+
+SELECT 'msg1' FROM pg_logical_send_message(true, 'test', 'msg1');
+SELECT 'msg2' FROM pg_logical_send_message(false, 'test', 'msg2');
+
+BEGIN;
+SELECT 'msg3' FROM pg_logical_send_message(true, 'test', 'msg3');
+SELECT 'msg4' FROM pg_logical_send_message(false, 'test', 'msg4');
+SELECT 'msg5' FROM pg_logical_send_message(true, 'test', 'msg5');
+COMMIT;
+
+SELECT regexp_replace(data, 'lsn: [^ ]+', '') FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'force-binary', '0', 'skip-empty-xacts', '1');
+
+SELECT 'init' FROM pg_drop_replication_slot('regression_slot');
diff --git a/contrib/test_decoding/test_decoding.c b/contrib/test_decoding/test_decoding.c
index 4cf808f..f655355 100644
--- a/contrib/test_decoding/test_decoding.c
+++ b/contrib/test_decoding/test_decoding.c
@@ -21,6 +21,7 @@
 
 #include "replication/output_plugin.h"
 #include "replication/logical.h"
+#include "replication/message.h"
 #include "replication/origin.h"
 
 #include "utils/builtins.h"
@@ -63,11 +64,15 @@ static void pg_decode_change(LogicalDecodingContext *ctx,
 				 ReorderBufferChange *change);
 static bool pg_decode_filter(LogicalDecodingContext *ctx,
 				 RepOriginId origin_id);
+static void pg_decode_message(LogicalDecodingContext *ctx,
+							  ReorderBufferTXN *txn, XLogRecPtr message_lsn,
+							  bool transactional, const char *prefix,
+							  Size sz, const char *message);
 
 void
 _PG_init(void)
 {
-	/* other plugins can perform things here */
+	RegisterLogicalMsgPrefix("test");
 }
 
 /* specify output plugin callbacks */
@@ -82,6 +87,7 @@ _PG_output_plugin_init(OutputPluginCallbacks *cb)
 	cb->commit_cb = pg_decode_commit_txn;
 	cb->filter_by_origin_cb = pg_decode_filter;
 	cb->shutdown_cb = pg_decode_shutdown;
+	cb->message_cb = pg_decode_message;
 }
 
 
@@ -471,3 +477,17 @@ pg_decode_change(LogicalDecodingContext *ctx, ReorderBufferTXN *txn,
 
 	OutputPluginWrite(ctx, true);
 }
+
+static void
+pg_decode_message(LogicalDecodingContext *ctx,
+				  ReorderBufferTXN *txn, XLogRecPtr lsn,
+				  bool transactional, const char *prefix,
+				  Size sz, const char *message)
+{
+	OutputPluginPrepareWrite(ctx, true);
+	appendStringInfo(ctx->out, "message: lsn: %X/%X transactional: %d prefix: %s, sz: %zu content:",
+					 (uint32)(lsn >> 32), (uint32)lsn, transactional, prefix,
+					 sz);
+	appendBinaryStringInfo(ctx->out, message, sz);
+	OutputPluginWrite(ctx, true);
+}
diff --git a/doc/src/sgml/func.sgml b/doc/src/sgml/func.sgml
index c0b94bc..c21d2c7 100644
--- a/doc/src/sgml/func.sgml
+++ b/doc/src/sgml/func.sgml
@@ -17769,6 +17769,48 @@ postgres=# SELECT * FROM pg_xlogfile_name_offset(pg_stop_backup());
        </entry>
       </row>
 
+      <row>
+       <entry id="pg-logical-send-message-text">
+        <indexterm>
+         <primary>pg_logical_send_message</primary>
+        </indexterm>
+        <literal><function>pg_logical_send_message(<parameter>transactional</parameter> <type>bool</type>, <parameter>prefix</parameter> <type>text</type>, <parameter>content</parameter> <type>text</type>)</function></literal>
+       </entry>
+       <entry>
+        void
+       </entry>
+       <entry>
+        Write text logical decoding message. This can be used to pass generic
+        messages to logical decoding plugins through WAL. The parameter
+        <parameter>transactional</parameter> specifies if the message should
+        be part of current transaction or if it should be written and decoded
+        immediately. The <parameter>prefix</parameter> has to be prefix which
+        was registered by a plugin. The <parameter>content</parameter> is
+        content of the message.
+       </entry>
+      </row>
+
+      <row>
+       <entry id="pg-logical-send-message-bytea">
+        <indexterm>
+         <primary>pg_logical_send_message</primary>
+        </indexterm>
+        <literal><function>pg_logical_send_message(<parameter>transactional</parameter> <type>bool</type>, <parameter>prefix</parameter> <type>text</type>, <parameter>content</parameter> <type>bytea</type>)</function></literal>
+       </entry>
+       <entry>
+        void
+       </entry>
+       <entry>
+        Write binary logical decoding message. This can be used to pass generic
+        messages to logical decoding plugins through WAL. The parameter
+        <parameter>transactional</parameter> specifies if the message should
+        be part of current transaction or if it should be written and decoded
+        immediately. The <parameter>prefix</parameter> has to be prefix which
+        was registered by a plugin. The <parameter>content</parameter> is
+        content of the message.
+       </entry>
+      </row>
+
      </tbody>
     </tgroup>
    </table>
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index e841348..01a2e78 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -363,6 +363,7 @@ typedef struct OutputPluginCallbacks
     LogicalDecodeBeginCB begin_cb;
     LogicalDecodeChangeCB change_cb;
     LogicalDecodeCommitCB commit_cb;
+    LogicalDecodeMessageCB message_cb;
     LogicalDecodeFilterByOriginCB filter_by_origin_cb;
     LogicalDecodeShutdownCB shutdown_cb;
 } OutputPluginCallbacks;
@@ -602,6 +603,27 @@ typedef bool (*LogicalDecodeFilterByOriginCB) (
        more efficient.
      </para>
      </sect3>
+
+    <sect3 id="logicaldecoding-output-plugin-message">
+     <title>Generic Message Callback</title>
+
+     <para>
+      The optional <function>message_cb</function> callback is called whenever
+      a logical decoding message has been decoded.
+<programlisting>
+typedef void (*LogicalDecodeMessageCB) (
+    struct LogicalDecodingContext *,
+    ReorderBufferTXN *txn,
+    XLogRecPtr message_lsn,
+    bool transactional,
+    const char *prefix,
+    Size message_size,
+    const char *message
+);
+</programlisting>
+     </para>
+    </sect3>
+
    </sect2>
 
    <sect2 id="logicaldecoding-output-plugin-output">
diff --git a/src/backend/access/rmgrdesc/Makefile b/src/backend/access/rmgrdesc/Makefile
index c72a1f2..723b4d8 100644
--- a/src/backend/access/rmgrdesc/Makefile
+++ b/src/backend/access/rmgrdesc/Makefile
@@ -9,8 +9,8 @@ top_builddir = ../../../..
 include $(top_builddir)/src/Makefile.global
 
 OBJS = brindesc.o clogdesc.o committsdesc.o dbasedesc.o gindesc.o gistdesc.o \
-	   hashdesc.o heapdesc.o mxactdesc.o nbtdesc.o relmapdesc.o \
-	   replorigindesc.o seqdesc.o smgrdesc.o spgdesc.o \
+	   hashdesc.o heapdesc.o logicalmsgdesc.o mxactdesc.o nbtdesc.o \
+	   relmapdesc.o replorigindesc.o seqdesc.o smgrdesc.o spgdesc.o \
 	   standbydesc.o tblspcdesc.o xactdesc.o xlogdesc.o
 
 include $(top_srcdir)/src/backend/common.mk
diff --git a/src/backend/access/rmgrdesc/logicalmsgdesc.c b/src/backend/access/rmgrdesc/logicalmsgdesc.c
new file mode 100644
index 0000000..739ee10
--- /dev/null
+++ b/src/backend/access/rmgrdesc/logicalmsgdesc.c
@@ -0,0 +1,33 @@
+/*-------------------------------------------------------------------------
+ *
+ * logicalmsgdesc.c
+ *	  rmgr descriptor routines for replication/logical/message.c
+ *
+ * Portions Copyright (c) 2015-2016, PostgreSQL Global Development Group
+ *
+ *
+ * IDENTIFICATION
+ *	  src/backend/access/rmgrdesc/logicalmsgdesc.c
+ *
+ *-------------------------------------------------------------------------
+ */
+#include "postgres.h"
+
+#include "replication/message.h"
+
+void
+logicalmsg_desc(StringInfo buf, XLogReaderState *record)
+{
+	char			   *rec = XLogRecGetData(record);
+	xl_logical_message *xlrec = (xl_logical_message *) rec;
+
+	appendStringInfo(buf, "%s message size %zu bytes",
+					 xlrec->transactional ? "transactional" : "nontransactional",
+					 xlrec->message_size);
+}
+
+const char *
+logicalmsg_identify(uint8 info)
+{
+	return NULL;
+}
diff --git a/src/backend/access/transam/rmgr.c b/src/backend/access/transam/rmgr.c
index 7c4d773..1a42121 100644
--- a/src/backend/access/transam/rmgr.c
+++ b/src/backend/access/transam/rmgr.c
@@ -23,6 +23,7 @@
 #include "commands/dbcommands_xlog.h"
 #include "commands/sequence.h"
 #include "commands/tablespace.h"
+#include "replication/message.h"
 #include "replication/origin.h"
 #include "storage/standby.h"
 #include "utils/relmapper.h"
diff --git a/src/backend/replication/logical/Makefile b/src/backend/replication/logical/Makefile
index 8adea13..1d7ca06 100644
--- a/src/backend/replication/logical/Makefile
+++ b/src/backend/replication/logical/Makefile
@@ -14,7 +14,7 @@ include $(top_builddir)/src/Makefile.global
 
 override CPPFLAGS := -I$(srcdir) $(CPPFLAGS)
 
-OBJS = decode.o logical.o logicalfuncs.o reorderbuffer.o origin.o \
+OBJS = decode.o logical.o logicalfuncs.o message.o origin.o reorderbuffer.o \
 	snapbuild.o
 
 include $(top_srcdir)/src/backend/common.mk
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index 88c3a49..110f958 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -39,6 +39,7 @@
 
 #include "replication/decode.h"
 #include "replication/logical.h"
+#include "replication/message.h"
 #include "replication/reorderbuffer.h"
 #include "replication/origin.h"
 #include "replication/snapbuild.h"
@@ -58,6 +59,7 @@ static void DecodeHeapOp(LogicalDecodingContext *ctx, XLogRecordBuffer *buf);
 static void DecodeHeap2Op(LogicalDecodingContext *ctx, XLogRecordBuffer *buf);
 static void DecodeXactOp(LogicalDecodingContext *ctx, XLogRecordBuffer *buf);
 static void DecodeStandbyOp(LogicalDecodingContext *ctx, XLogRecordBuffer *buf);
+static void DecodeLogicalMsgOp(LogicalDecodingContext *ctx, XLogRecordBuffer *buf);
 
 /* individual record(group)'s handlers */
 static void DecodeInsert(LogicalDecodingContext *ctx, XLogRecordBuffer *buf);
@@ -115,6 +117,10 @@ LogicalDecodingProcessRecord(LogicalDecodingContext *ctx, XLogReaderState *recor
 			DecodeHeapOp(ctx, &buf);
 			break;
 
+		case RM_LOGICALMSG_ID:
+			DecodeLogicalMsgOp(ctx, &buf);
+			break;
+
 			/*
 			 * Rmgrs irrelevant for logical decoding; they describe stuff not
 			 * represented in logical decoding. Add new rmgrs in rmgrlist.h's
@@ -431,6 +437,37 @@ DecodeHeapOp(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
 	}
 }
 
+/*
+ * Handle rmgr LOGICALMSG_ID records for DecodeRecordIntoReorderBuffer().
+ */
+static void
+DecodeLogicalMsgOp(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
+{
+	SnapBuild  *builder = ctx->snapshot_builder;
+	XLogReaderState *r = buf->record;
+	uint8		info = XLogRecGetInfo(r) & ~XLR_INFO_MASK;
+	xl_logical_message *message;
+
+	if (info != XLOG_LOGICAL_MESSAGE)
+		elog(ERROR, "unexpected RM_LOGICALMSG_ID record type: %u", info);
+
+	message = (xl_logical_message *) XLogRecGetData(r);
+
+	if (message->transactional &&
+		!SnapBuildProcessChange(builder, XLogRecGetXid(r), buf->origptr))
+		return;
+	else if(!message->transactional &&
+			(SnapBuildCurrentState(ctx->snapshot_builder) != SNAPBUILD_CONSISTENT ||
+			 SnapBuildXactNeedsSkip(builder, buf->origptr)))
+		return;
+
+	ReorderBufferQueueMessage(ctx->reorder, XLogRecGetXid(r),
+							  buf->endptr, message->transactional,
+							  message->message, /* first part of message is prefix */
+							  message->message_size,
+							  message->message + message->prefix_size);
+}
+
 static inline bool
 FilterByOrigin(LogicalDecodingContext *ctx, RepOriginId origin_id)
 {
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index 2e6d3f9..998fb79 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -62,6 +62,9 @@ static void commit_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
 				  XLogRecPtr commit_lsn);
 static void change_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
 				  Relation relation, ReorderBufferChange *change);
+static void message_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
+				  XLogRecPtr message_lsn, bool transactional,
+				  const char *prefix, Size sz, const char *message);
 
 static void LoadOutputPlugin(OutputPluginCallbacks *callbacks, char *plugin);
 
@@ -178,6 +181,7 @@ StartupDecodingContext(List *output_plugin_options,
 	ctx->reorder->begin = begin_cb_wrapper;
 	ctx->reorder->apply_change = change_cb_wrapper;
 	ctx->reorder->commit = commit_cb_wrapper;
+	ctx->reorder->message = message_cb_wrapper;
 
 	ctx->out = makeStringInfo();
 	ctx->prepare_write = prepare_write;
@@ -702,6 +706,40 @@ filter_by_origin_cb_wrapper(LogicalDecodingContext *ctx, RepOriginId origin_id)
 	return ret;
 }
 
+static void message_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
+							   XLogRecPtr message_lsn,
+							   bool transactional, const char *prefix,
+							   Size sz, const char *message)
+{
+	LogicalDecodingContext *ctx = cache->private_data;
+	LogicalErrorCallbackState state;
+	ErrorContextCallback errcallback;
+
+	if (ctx->callbacks.message_cb == NULL)
+		return;
+
+	/* Push callback + info on the error context stack */
+	state.ctx = ctx;
+	state.callback_name = "message";
+	state.report_location = message_lsn; /* beginning of commit record */
+	errcallback.callback = output_plugin_error_callback;
+	errcallback.arg = (void *) &state;
+	errcallback.previous = error_context_stack;
+	error_context_stack = &errcallback;
+
+	/* set output state */
+	ctx->accept_writes = true;
+	ctx->write_xid = txn != NULL ? txn->xid : InvalidTransactionId;
+	ctx->write_location = message_lsn;
+
+	/* do the actual work: call callback */
+	ctx->callbacks.message_cb(ctx, txn, message_lsn, transactional,
+							  prefix, sz, message);
+
+	/* Pop the error context stack */
+	error_context_stack = errcallback.previous;
+}
+
 /*
  * Set the required catalog xmin horizon for historic snapshots in the current
  * replication slot.
diff --git a/src/backend/replication/logical/logicalfuncs.c b/src/backend/replication/logical/logicalfuncs.c
index f789fc1..2eb26d4 100644
--- a/src/backend/replication/logical/logicalfuncs.c
+++ b/src/backend/replication/logical/logicalfuncs.c
@@ -24,6 +24,8 @@
 #include "access/xlog_internal.h"
 #include "access/xlogutils.h"
 
+#include "access/xact.h"
+
 #include "catalog/pg_type.h"
 
 #include "nodes/makefuncs.h"
@@ -41,6 +43,7 @@
 #include "replication/decode.h"
 #include "replication/logical.h"
 #include "replication/logicalfuncs.h"
+#include "replication/message.h"
 
 #include "storage/fd.h"
 
@@ -363,3 +366,27 @@ pg_logical_slot_peek_binary_changes(PG_FUNCTION_ARGS)
 {
 	return pg_logical_slot_get_changes_guts(fcinfo, false, true);
 }
+
+
+/*
+ * SQL function returning the changestream in binary, only peeking ahead.
+ */
+Datum
+pg_logical_send_message_bytea(PG_FUNCTION_ARGS)
+{
+	bool		transactional = PG_GETARG_BOOL(0);
+	char	   *prefix = text_to_cstring(PG_GETARG_TEXT_PP(1));
+	bytea	   *data = PG_GETARG_BYTEA_PP(2);
+	XLogRecPtr	lsn;
+
+	lsn = LogLogicalMessage(prefix, VARDATA_ANY(data), VARSIZE_ANY_EXHDR(data),
+							transactional);
+	PG_RETURN_LSN(lsn);
+}
+
+Datum
+pg_logical_send_message_text(PG_FUNCTION_ARGS)
+{
+	/* bytea and text are compatible */
+	return pg_logical_send_message_bytea(fcinfo);
+}
diff --git a/src/backend/replication/logical/message.c b/src/backend/replication/logical/message.c
new file mode 100644
index 0000000..e5f4feb
--- /dev/null
+++ b/src/backend/replication/logical/message.c
@@ -0,0 +1,132 @@
+/*-------------------------------------------------------------------------
+ *
+ * message.c
+ *	  Generic logical messages.
+ *
+ * Copyright (c) 2013-2016, PostgreSQL Global Development Group
+ *
+ * IDENTIFICATION
+ *	  src/backend/replication/logical/message.c
+ *
+ * NOTES
+ *
+ * Generic logical messages allow XLOG logging of arbitrary binary blobs that
+ * get passed to the logical decoding plugin. In normal XLOG processing they
+ * are same as NOOP.
+ *
+ * These messages can be either transactional or non-transactional.
+ * Transactional messages are part of current transaction and will be sent to
+ * decoding plugin using in a same way as DML operations.
+ * Non-transactional messages are sent to the plugin at the time when the
+ * logical decoding reads them from XLOG.
+ *
+ * Every message carries prefix to avoid conflicts between different decoding
+ * plugins. The prefix has to be registered before the message using that
+ * prefix can be written to XLOG. The prefix can be registered exactly once to
+ * avoid situation where multiple third party extensions try to use same
+ * prefix.
+ *
+ * ---------------------------------------------------------------------------
+ */
+
+#include "postgres.h"
+
+#include "access/xact.h"
+
+#include "catalog/indexing.h"
+
+#include "nodes/execnodes.h"
+
+#include "replication/message.h"
+#include "replication/logical.h"
+
+#include "utils/memutils.h"
+
+/* List of registered logical message prefixes. */
+static List	   *LogicalMsgPrefixList = NIL;
+
+XLogRecPtr
+LogLogicalMessage(const char *prefix, const char *message, size_t size,
+				  bool transactional)
+{
+	ListCell		   *lc;
+	bool				found = false;
+	xl_logical_message	xlrec;
+
+	/* Check if the provided prefix is known to us. */
+	foreach(lc, LogicalMsgPrefixList)
+	{
+		char	*mp = lfirst(lc);
+
+		if (strcmp(prefix, mp) == 0)
+		{
+			found = true;
+			break;
+		}
+	}
+	if (!found)
+		ereport(ERROR,
+				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+				 errmsg("standby message prefix \"%s\" is not registered",
+						prefix)));
+
+	/*
+	 * Force xid to be allocated if we're sending a transactional message.
+	 */
+	if (transactional)
+	{
+		Assert(IsTransactionState());
+		GetCurrentTransactionId();
+	}
+
+	xlrec.transactional = transactional;
+	xlrec.prefix_size = strlen(prefix) + 1;
+	xlrec.message_size = size;
+
+	XLogBeginInsert();
+	XLogRegisterData((char *) &xlrec, SizeOfLogicalMessage);
+	XLogRegisterData((char *) prefix, xlrec.prefix_size);
+	XLogRegisterData((char *) message, size);
+
+	return XLogInsert(RM_LOGICALMSG_ID, XLOG_LOGICAL_MESSAGE);
+}
+
+void
+RegisterLogicalMsgPrefix(const char *prefix)
+{
+	ListCell	   *lc;
+	bool			found = false;
+	MemoryContext	oldcxt;
+
+	/* Check for duplicit registrations. */
+	foreach(lc, LogicalMsgPrefixList)
+	{
+		char	*mp = lfirst(lc);
+
+		if (strcmp(prefix, mp) == 0)
+		{
+			found = true;
+			break;
+		}
+	}
+	if (found)
+		ereport(ERROR,
+				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+				 errmsg("logical decoding message prefix \"%s\" is already registered",
+						prefix)));
+
+	oldcxt = MemoryContextSwitchTo(TopMemoryContext);
+	LogicalMsgPrefixList = lappend(LogicalMsgPrefixList, pstrdup(prefix));
+	MemoryContextSwitchTo(oldcxt);
+}
+
+void
+logicalmsg_redo(XLogReaderState *record)
+{
+	uint8		info = XLogRecGetInfo(record) & ~XLR_INFO_MASK;
+
+	if (info != XLOG_LOGICAL_MESSAGE)
+			elog(PANIC, "logicalmsg_redo: unknown op code %u", info);
+
+	/* This is only interesting for logical decoding, see decode.c. */
+}
diff --git a/src/backend/replication/logical/reorderbuffer.c b/src/backend/replication/logical/reorderbuffer.c
index 78acced..99e9ec7 100644
--- a/src/backend/replication/logical/reorderbuffer.c
+++ b/src/backend/replication/logical/reorderbuffer.c
@@ -414,6 +414,11 @@ ReorderBufferReturnChange(ReorderBuffer *rb, ReorderBufferChange *change)
 				change->data.tp.oldtuple = NULL;
 			}
 			break;
+		case REORDER_BUFFER_CHANGE_MESSAGE:
+			if (change->data.msg.message != NULL)
+				pfree(change->data.msg.message);
+			change->data.msg.message = NULL;
+			break;
 		case REORDER_BUFFER_CHANGE_INTERNAL_SNAPSHOT:
 			if (change->data.snapshot)
 			{
@@ -599,6 +604,39 @@ ReorderBufferQueueChange(ReorderBuffer *rb, TransactionId xid, XLogRecPtr lsn,
 	ReorderBufferCheckSerializeTXN(rb, txn);
 }
 
+void
+ReorderBufferQueueMessage(ReorderBuffer *rb, TransactionId xid, XLogRecPtr lsn,
+						  bool transactional, const char *prefix, Size msg_sz,
+						  const char *msg)
+{
+	ReorderBufferTXN *txn = NULL;
+
+	if (transactional)
+	{
+		ReorderBufferChange *change;
+
+		txn = ReorderBufferTXNByXid(rb, xid, true, NULL, lsn, true);
+
+		Assert(xid != InvalidTransactionId);
+		Assert(txn != NULL);
+
+		change = ReorderBufferGetChange(rb);
+		change->action = REORDER_BUFFER_CHANGE_MESSAGE;
+		change->data.msg.transactional = true;
+		change->data.msg.prefix = pstrdup(prefix);
+		change->data.msg.message_size = msg_sz;
+		change->data.msg.message = palloc(msg_sz);
+		memcpy(change->data.msg.message, msg, msg_sz);
+
+		ReorderBufferQueueChange(rb, xid, lsn, change);
+	}
+	else
+	{
+		rb->message(rb, txn, lsn, transactional, prefix, msg_sz, msg);
+	}
+}
+
+
 static void
 AssertTXNLsnOrder(ReorderBuffer *rb)
 {
@@ -1465,6 +1503,14 @@ ReorderBufferCommit(ReorderBuffer *rb, TransactionId xid,
 					specinsert = change;
 					break;
 
+				case REORDER_BUFFER_CHANGE_MESSAGE:
+					rb->message(rb, txn, change->lsn,
+								change->data.msg.transactional,
+								change->data.msg.prefix,
+								change->data.msg.message_size,
+								change->data.msg.message);
+					break;
+
 				case REORDER_BUFFER_CHANGE_INTERNAL_SNAPSHOT:
 					/* get rid of the old */
 					TeardownHistoricSnapshot(false);
@@ -2117,6 +2163,21 @@ ReorderBufferSerializeChange(ReorderBuffer *rb, ReorderBufferTXN *txn,
 				}
 				break;
 			}
+		case REORDER_BUFFER_CHANGE_MESSAGE:
+			{
+				char	   *data;
+				size_t		prefix_size = strlen(change->data.msg.prefix) + 1;
+
+				sz += prefix_size + change->data.msg.message_size;
+				ReorderBufferSerializeReserve(rb, sz);
+
+				data = ((char *) rb->outbuf) + sizeof(ReorderBufferDiskChange);
+				memcpy(data, change->data.msg.prefix,
+					   prefix_size);
+				memcpy(data + prefix_size, change->data.msg.message,
+					   change->data.msg.message_size);
+				break;
+			}
 		case REORDER_BUFFER_CHANGE_INTERNAL_SNAPSHOT:
 			{
 				Snapshot	snap;
@@ -2354,6 +2415,18 @@ ReorderBufferRestoreChange(ReorderBuffer *rb, ReorderBufferTXN *txn,
 				data += len;
 			}
 			break;
+		case REORDER_BUFFER_CHANGE_MESSAGE:
+			{
+				Size		message_size = change->data.msg.message_size;
+				Size		prefix_size = strlen(data) + 1;
+
+				change->data.msg.prefix = pstrdup(data);
+				change->data.msg.message = palloc(message_size);
+				memcpy(change->data.msg.message, data + prefix_size,
+					   message_size);
+
+				data += prefix_size + message_size;
+			}
 		case REORDER_BUFFER_CHANGE_INTERNAL_SNAPSHOT:
 			{
 				Snapshot	oldsnap;
diff --git a/src/bin/pg_xlogdump/rmgrdesc.c b/src/bin/pg_xlogdump/rmgrdesc.c
index f9cd395..6ba7f22 100644
--- a/src/bin/pg_xlogdump/rmgrdesc.c
+++ b/src/bin/pg_xlogdump/rmgrdesc.c
@@ -25,6 +25,7 @@
 #include "commands/dbcommands_xlog.h"
 #include "commands/sequence.h"
 #include "commands/tablespace.h"
+#include "replication/message.h"
 #include "replication/origin.h"
 #include "rmgrdesc.h"
 #include "storage/standbydefs.h"
diff --git a/src/include/access/rmgrlist.h b/src/include/access/rmgrlist.h
index fab912d..35c242d 100644
--- a/src/include/access/rmgrlist.h
+++ b/src/include/access/rmgrlist.h
@@ -45,3 +45,4 @@ PG_RMGR(RM_SPGIST_ID, "SPGist", spg_redo, spg_desc, spg_identify, spg_xlog_start
 PG_RMGR(RM_BRIN_ID, "BRIN", brin_redo, brin_desc, brin_identify, NULL, NULL)
 PG_RMGR(RM_COMMIT_TS_ID, "CommitTs", commit_ts_redo, commit_ts_desc, commit_ts_identify, NULL, NULL)
 PG_RMGR(RM_REPLORIGIN_ID, "ReplicationOrigin", replorigin_redo, replorigin_desc, replorigin_identify, NULL, NULL)
+PG_RMGR(RM_LOGICALMSG_ID, "LogicalMessage", logicalmsg_redo, logicalmsg_desc, logicalmsg_identify, NULL, NULL)
diff --git a/src/include/catalog/pg_proc.h b/src/include/catalog/pg_proc.h
index 62b9125..76e41cd 100644
--- a/src/include/catalog/pg_proc.h
+++ b/src/include/catalog/pg_proc.h
@@ -5084,6 +5084,10 @@ DATA(insert OID = 3784 (  pg_logical_slot_peek_changes PGNSP PGUID 12 1000 1000
 DESCR("peek at changes from replication slot");
 DATA(insert OID = 3785 (  pg_logical_slot_peek_binary_changes PGNSP PGUID 12 1000 1000 25 0 f f f f f t v u 4 0 2249 "19 3220 23 1009" "{19,3220,23,1009,3220,28,17}" "{i,i,i,v,o,o,o}" "{slot_name,upto_lsn,upto_nchanges,options,location,xid,data}" _null_ _null_ pg_logical_slot_peek_binary_changes _null_ _null_ _null_ ));
 DESCR("peek at binary changes from replication slot");
+DATA(insert OID = 3577 (  pg_logical_send_message PGNSP PGUID 12 1 0 0 0 f f f f f f v u 3 0 3220 "16 25 25" _null_ _null_ _null_ _null_ _null_ pg_logical_send_message_text _null_ _null_ _null_ ));
+DESCR("send a textual message");
+DATA(insert OID = 3578 (  pg_logical_send_message PGNSP PGUID 12 1 0 0 0 f f f f f f v u 3 0 3220 "16 25 17" _null_ _null_ _null_ _null_ _null_ pg_logical_send_message_bytea _null_ _null_ _null_ ));
+DESCR("send a binary message");
 
 /* event triggers */
 DATA(insert OID = 3566 (  pg_event_trigger_dropped_objects		PGNSP PGUID 12 10 100 0 0 f f f f t t s s 0 0 2249 "" "{26,26,23,16,16,16,25,25,25,25,1009,1009}" "{o,o,o,o,o,o,o,o,o,o,o,o}" "{classid, objid, objsubid, original, normal, is_temporary, object_type, schema_name, object_name, object_identity, address_names, address_args}" _null_ _null_ pg_event_trigger_dropped_objects _null_ _null_ _null_ ));
diff --git a/src/include/replication/logicalfuncs.h b/src/include/replication/logicalfuncs.h
index c87a1df..cd3373e 100644
--- a/src/include/replication/logicalfuncs.h
+++ b/src/include/replication/logicalfuncs.h
@@ -21,4 +21,6 @@ extern Datum pg_logical_slot_get_binary_changes(PG_FUNCTION_ARGS);
 extern Datum pg_logical_slot_peek_changes(PG_FUNCTION_ARGS);
 extern Datum pg_logical_slot_peek_binary_changes(PG_FUNCTION_ARGS);
 
+extern Datum pg_logical_send_message_bytea(PG_FUNCTION_ARGS);
+extern Datum pg_logical_send_message_text(PG_FUNCTION_ARGS);
 #endif
diff --git a/src/include/replication/message.h b/src/include/replication/message.h
new file mode 100644
index 0000000..e4223f4
--- /dev/null
+++ b/src/include/replication/message.h
@@ -0,0 +1,42 @@
+/*-------------------------------------------------------------------------
+ * message.h
+ *	   Exports from replication/logical/message.c
+ *
+ * Copyright (c) 2013-2016, PostgreSQL Global Development Group
+ *
+ * src/include/replication/message.h
+ *-------------------------------------------------------------------------
+ */
+#ifndef PG_LOGICAL_MESSAGE_H
+#define PG_LOGICAL_MESSAGE_H
+
+#include "access/xlog.h"
+#include "access/xlogdefs.h"
+#include "access/xlogreader.h"
+
+/*
+ * Generic logical decoding message wal record.
+ */
+typedef struct xl_logical_message
+{
+	bool		transactional;					/* is message transactional? */
+	size_t		prefix_size;					/* length of prefix */
+	size_t		message_size;					/* size of the message */
+	char		message[FLEXIBLE_ARRAY_MEMBER];	/* message including the null
+												 * terminated prefx of length
+												 * prefix_size */
+} xl_logical_message;
+
+#define SizeOfLogicalMessage	(offsetof(xl_logical_message, message))
+
+extern XLogRecPtr LogLogicalMessage(const char *prefix, const char *message,
+									size_t size, bool transactional);
+extern void RegisterLogicalMsgPrefix(const char *prefix);
+
+/* RMGR API*/
+#define XLOG_LOGICAL_MESSAGE	0x00
+void		logicalmsg_redo(XLogReaderState *record);
+void		logicalmsg_desc(StringInfo buf, XLogReaderState *record);
+const char *logicalmsg_identify(uint8 info);
+
+#endif   /* PG_LOGICAL_MESSAGE_H */
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 577b12e..3a2ca98 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -74,6 +74,18 @@ typedef void (*LogicalDecodeCommitCB) (
 												   XLogRecPtr commit_lsn);
 
 /*
+ * Called for the generic logical decoding messages.
+ */
+typedef void (*LogicalDecodeMessageCB) (
+											 struct LogicalDecodingContext *,
+											 ReorderBufferTXN *txn,
+											 XLogRecPtr message_lsn,
+											 bool transactional,
+											 const char *prefix,
+											 Size message_size,
+											 const char *message);
+
+/*
  * Filter changes by origin.
  */
 typedef bool (*LogicalDecodeFilterByOriginCB) (
@@ -96,6 +108,7 @@ typedef struct OutputPluginCallbacks
 	LogicalDecodeBeginCB begin_cb;
 	LogicalDecodeChangeCB change_cb;
 	LogicalDecodeCommitCB commit_cb;
+	LogicalDecodeMessageCB message_cb;
 	LogicalDecodeFilterByOriginCB filter_by_origin_cb;
 	LogicalDecodeShutdownCB shutdown_cb;
 } OutputPluginCallbacks;
diff --git a/src/include/replication/reorderbuffer.h b/src/include/replication/reorderbuffer.h
index 2abee0a..f51f5c1 100644
--- a/src/include/replication/reorderbuffer.h
+++ b/src/include/replication/reorderbuffer.h
@@ -51,6 +51,7 @@ enum ReorderBufferChangeType
 	REORDER_BUFFER_CHANGE_INSERT,
 	REORDER_BUFFER_CHANGE_UPDATE,
 	REORDER_BUFFER_CHANGE_DELETE,
+	REORDER_BUFFER_CHANGE_MESSAGE,
 	REORDER_BUFFER_CHANGE_INTERNAL_SNAPSHOT,
 	REORDER_BUFFER_CHANGE_INTERNAL_COMMAND_ID,
 	REORDER_BUFFER_CHANGE_INTERNAL_TUPLECID,
@@ -95,6 +96,14 @@ typedef struct ReorderBufferChange
 			ReorderBufferTupleBuf *newtuple;
 		}			tp;
 
+		struct
+		{
+			bool transactional;
+			char *prefix;
+			size_t message_size;
+			char *message;
+		} msg;
+
 		/* New snapshot, set when action == *_INTERNAL_SNAPSHOT */
 		Snapshot	snapshot;
 
@@ -271,6 +280,15 @@ typedef void (*ReorderBufferCommitCB) (
 												   ReorderBufferTXN *txn,
 												   XLogRecPtr commit_lsn);
 
+/* message callback signature */
+typedef void (*ReorderBufferMessageCB) (
+												   ReorderBuffer *rb,
+												   ReorderBufferTXN *txn,
+												   XLogRecPtr message_lsn,
+												   bool transactional,
+												   const char *prefix, Size sz,
+												   const char *message);
+
 struct ReorderBuffer
 {
 	/*
@@ -297,6 +315,7 @@ struct ReorderBuffer
 	ReorderBufferBeginCB begin;
 	ReorderBufferApplyChangeCB apply_change;
 	ReorderBufferCommitCB commit;
+	ReorderBufferMessageCB message;
 
 	/*
 	 * Pointer that will be passed untouched to the callbacks.
@@ -347,6 +366,8 @@ ReorderBufferChange *ReorderBufferGetChange(ReorderBuffer *);
 void		ReorderBufferReturnChange(ReorderBuffer *, ReorderBufferChange *);
 
 void		ReorderBufferQueueChange(ReorderBuffer *, TransactionId, XLogRecPtr lsn, ReorderBufferChange *);
+void		ReorderBufferQueueMessage(ReorderBuffer *, TransactionId, XLogRecPtr lsn,
+									  bool transactional, const char *prefix, Size msg_sz, const char *msg);
 void ReorderBufferCommit(ReorderBuffer *, TransactionId,
 					XLogRecPtr commit_lsn, XLogRecPtr end_lsn,
 	  TimestampTz commit_time, RepOriginId origin_id, XLogRecPtr origin_lsn);
-- 
1.9.1

From 2f037a757d9cec09f04457d82cdd1256b8255b78 Mon Sep 17 00:00:00 2001
From: Petr Jelinek <pjmodos@pjmodos.net>
Date: Wed, 24 Feb 2016 17:02:36 +0100
Subject: [PATCH] Logical Decoding Messages

---
 contrib/test_decoding/Makefile                  |  2 +-
 contrib/test_decoding/expected/ddl.out          | 21 ++++--
 contrib/test_decoding/expected/messages.out     | 56 ++++++++++++++++
 contrib/test_decoding/sql/ddl.sql               |  3 +-
 contrib/test_decoding/sql/messages.sql          | 17 +++++
 contrib/test_decoding/test_decoding.c           | 19 ++++++
 doc/src/sgml/func.sgml                          | 45 +++++++++++++
 doc/src/sgml/logicaldecoding.sgml               | 37 +++++++++++
 src/backend/access/rmgrdesc/Makefile            |  4 +-
 src/backend/access/rmgrdesc/logicalmsgdesc.c    | 41 ++++++++++++
 src/backend/access/transam/rmgr.c               |  1 +
 src/backend/replication/logical/Makefile        |  2 +-
 src/backend/replication/logical/decode.c        | 49 ++++++++++++++
 src/backend/replication/logical/logical.c       | 38 +++++++++++
 src/backend/replication/logical/logicalfuncs.c  | 27 ++++++++
 src/backend/replication/logical/message.c       | 87 +++++++++++++++++++++++++
 src/backend/replication/logical/reorderbuffer.c | 67 +++++++++++++++++++
 src/backend/replication/logical/snapbuild.c     | 19 ++++++
 src/bin/pg_xlogdump/rmgrdesc.c                  |  1 +
 src/include/access/rmgrlist.h                   |  1 +
 src/include/catalog/pg_proc.h                   |  4 ++
 src/include/replication/logicalfuncs.h          |  2 +
 src/include/replication/message.h               | 41 ++++++++++++
 src/include/replication/output_plugin.h         | 13 ++++
 src/include/replication/reorderbuffer.h         | 21 ++++++
 src/include/replication/snapbuild.h             |  2 +
 26 files changed, 608 insertions(+), 12 deletions(-)
 create mode 100644 contrib/test_decoding/expected/messages.out
 create mode 100644 contrib/test_decoding/sql/messages.sql
 create mode 100644 src/backend/access/rmgrdesc/logicalmsgdesc.c
 create mode 100644 src/backend/replication/logical/message.c
 create mode 100644 src/include/replication/message.h

diff --git a/contrib/test_decoding/Makefile b/contrib/test_decoding/Makefile
index a362e69..8fdcfbc 100644
--- a/contrib/test_decoding/Makefile
+++ b/contrib/test_decoding/Makefile
@@ -38,7 +38,7 @@ submake-test_decoding:
 	$(MAKE) -C $(top_builddir)/contrib/test_decoding
 
 REGRESSCHECKS=ddl rewrite toast permissions decoding_in_xact decoding_into_rel \
-	binary prepared replorigin
+	binary prepared replorigin messages
 
 regresscheck: | submake-regress submake-test_decoding temp-install
 	$(MKDIR_P) regression_output
diff --git a/contrib/test_decoding/expected/ddl.out b/contrib/test_decoding/expected/ddl.out
index 57a1289..4d13ad4 100644
--- a/contrib/test_decoding/expected/ddl.out
+++ b/contrib/test_decoding/expected/ddl.out
@@ -220,11 +220,17 @@ SELECT data FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'inc
 (7 rows)
 
 /*
- * check that disk spooling works
+ * check that disk spooling works (also for logical messages)
  */
 BEGIN;
 CREATE TABLE tr_etoomuch (id serial primary key, data int);
 INSERT INTO tr_etoomuch(data) SELECT g.i FROM generate_series(1, 10234) g(i);
+SELECT 'tx logical msg' FROM pg_logical_emit_message(true, 'test', 'tx logical msg');
+    ?column?    
+----------------
+ tx logical msg
+(1 row)
+
 DELETE FROM tr_etoomuch WHERE id < 5000;
 UPDATE tr_etoomuch SET data = - data WHERE id > 5000;
 COMMIT;
@@ -233,12 +239,13 @@ SELECT count(*), min(data), max(data)
 FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'include-xids', '0', 'skip-empty-xacts', '1')
 GROUP BY substring(data, 1, 24)
 ORDER BY 1,2;
- count |                       min                       |                                  max                                   
--------+-------------------------------------------------+------------------------------------------------------------------------
-     1 | BEGIN                                           | BEGIN
-     1 | COMMIT                                          | COMMIT
- 20467 | table public.tr_etoomuch: DELETE: id[integer]:1 | table public.tr_etoomuch: UPDATE: id[integer]:9999 data[integer]:-9999
-(3 rows)
+ count |                                  min                                  |                                  max                                   
+-------+-----------------------------------------------------------------------+------------------------------------------------------------------------
+     1 | BEGIN                                                                 | BEGIN
+     1 | COMMIT                                                                | COMMIT
+     1 | message: transactional: 1 prefix: test, sz: 14 content:tx logical msg | message: transactional: 1 prefix: test, sz: 14 content:tx logical msg
+ 20467 | table public.tr_etoomuch: DELETE: id[integer]:1                       | table public.tr_etoomuch: UPDATE: id[integer]:9999 data[integer]:-9999
+(4 rows)
 
 -- check that a large, spooled, upsert works
 INSERT INTO tr_etoomuch (id, data)
diff --git a/contrib/test_decoding/expected/messages.out b/contrib/test_decoding/expected/messages.out
new file mode 100644
index 0000000..7fa8256
--- /dev/null
+++ b/contrib/test_decoding/expected/messages.out
@@ -0,0 +1,56 @@
+-- predictability
+SET synchronous_commit = on;
+SELECT 'init' FROM pg_create_logical_replication_slot('regression_slot', 'test_decoding');
+ ?column? 
+----------
+ init
+(1 row)
+
+SELECT 'msg1' FROM pg_logical_emit_message(true, 'test', 'msg1');
+ ?column? 
+----------
+ msg1
+(1 row)
+
+SELECT 'msg2' FROM pg_logical_emit_message(false, 'test', 'msg2');
+ ?column? 
+----------
+ msg2
+(1 row)
+
+BEGIN;
+SELECT 'msg3' FROM pg_logical_emit_message(true, 'test', 'msg3');
+ ?column? 
+----------
+ msg3
+(1 row)
+
+SELECT 'msg4' FROM pg_logical_emit_message(false, 'test', 'msg4');
+ ?column? 
+----------
+ msg4
+(1 row)
+
+SELECT 'msg5' FROM pg_logical_emit_message(true, 'test', 'msg5');
+ ?column? 
+----------
+ msg5
+(1 row)
+
+COMMIT;
+SELECT data FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'force-binary', '0', 'skip-empty-xacts', '1');
+                            data                            
+------------------------------------------------------------
+ message: transactional: 1 prefix: test, sz: 4 content:msg1
+ message: transactional: 0 prefix: test, sz: 4 content:msg2
+ message: transactional: 0 prefix: test, sz: 4 content:msg4
+ message: transactional: 1 prefix: test, sz: 4 content:msg3
+ message: transactional: 1 prefix: test, sz: 4 content:msg5
+(5 rows)
+
+SELECT 'init' FROM pg_drop_replication_slot('regression_slot');
+ ?column? 
+----------
+ init
+(1 row)
+
diff --git a/contrib/test_decoding/sql/ddl.sql b/contrib/test_decoding/sql/ddl.sql
index e311c59..2f31784 100644
--- a/contrib/test_decoding/sql/ddl.sql
+++ b/contrib/test_decoding/sql/ddl.sql
@@ -108,11 +108,12 @@ DELETE FROM tr_pkey;
 SELECT data FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'include-xids', '0', 'skip-empty-xacts', '1');
 
 /*
- * check that disk spooling works
+ * check that disk spooling works (also for logical messages)
  */
 BEGIN;
 CREATE TABLE tr_etoomuch (id serial primary key, data int);
 INSERT INTO tr_etoomuch(data) SELECT g.i FROM generate_series(1, 10234) g(i);
+SELECT 'tx logical msg' FROM pg_logical_emit_message(true, 'test', 'tx logical msg');
 DELETE FROM tr_etoomuch WHERE id < 5000;
 UPDATE tr_etoomuch SET data = - data WHERE id > 5000;
 COMMIT;
diff --git a/contrib/test_decoding/sql/messages.sql b/contrib/test_decoding/sql/messages.sql
new file mode 100644
index 0000000..8744eb6
--- /dev/null
+++ b/contrib/test_decoding/sql/messages.sql
@@ -0,0 +1,17 @@
+-- predictability
+SET synchronous_commit = on;
+
+SELECT 'init' FROM pg_create_logical_replication_slot('regression_slot', 'test_decoding');
+
+SELECT 'msg1' FROM pg_logical_emit_message(true, 'test', 'msg1');
+SELECT 'msg2' FROM pg_logical_emit_message(false, 'test', 'msg2');
+
+BEGIN;
+SELECT 'msg3' FROM pg_logical_emit_message(true, 'test', 'msg3');
+SELECT 'msg4' FROM pg_logical_emit_message(false, 'test', 'msg4');
+SELECT 'msg5' FROM pg_logical_emit_message(true, 'test', 'msg5');
+COMMIT;
+
+SELECT data FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'force-binary', '0', 'skip-empty-xacts', '1');
+
+SELECT 'init' FROM pg_drop_replication_slot('regression_slot');
diff --git a/contrib/test_decoding/test_decoding.c b/contrib/test_decoding/test_decoding.c
index 4cf808f..6395ffd 100644
--- a/contrib/test_decoding/test_decoding.c
+++ b/contrib/test_decoding/test_decoding.c
@@ -21,6 +21,7 @@
 
 #include "replication/output_plugin.h"
 #include "replication/logical.h"
+#include "replication/message.h"
 #include "replication/origin.h"
 
 #include "utils/builtins.h"
@@ -63,6 +64,10 @@ static void pg_decode_change(LogicalDecodingContext *ctx,
 				 ReorderBufferChange *change);
 static bool pg_decode_filter(LogicalDecodingContext *ctx,
 				 RepOriginId origin_id);
+static void pg_decode_message(LogicalDecodingContext *ctx,
+							  ReorderBufferTXN *txn, XLogRecPtr message_lsn,
+							  bool transactional, const char *prefix,
+							  Size sz, const char *message);
 
 void
 _PG_init(void)
@@ -82,6 +87,7 @@ _PG_output_plugin_init(OutputPluginCallbacks *cb)
 	cb->commit_cb = pg_decode_commit_txn;
 	cb->filter_by_origin_cb = pg_decode_filter;
 	cb->shutdown_cb = pg_decode_shutdown;
+	cb->message_cb = pg_decode_message;
 }
 
 
@@ -471,3 +477,16 @@ pg_decode_change(LogicalDecodingContext *ctx, ReorderBufferTXN *txn,
 
 	OutputPluginWrite(ctx, true);
 }
+
+static void
+pg_decode_message(LogicalDecodingContext *ctx,
+				  ReorderBufferTXN *txn, XLogRecPtr lsn,
+				  bool transactional, const char *prefix,
+				  Size sz, const char *message)
+{
+	OutputPluginPrepareWrite(ctx, true);
+	appendStringInfo(ctx->out, "message: transactional: %d prefix: %s, sz: %zu content:",
+					 transactional, prefix, sz);
+	appendBinaryStringInfo(ctx->out, message, sz);
+	OutputPluginWrite(ctx, true);
+}
diff --git a/doc/src/sgml/func.sgml b/doc/src/sgml/func.sgml
index c0b94bc..1201f9f 100644
--- a/doc/src/sgml/func.sgml
+++ b/doc/src/sgml/func.sgml
@@ -17769,6 +17769,51 @@ postgres=# SELECT * FROM pg_xlogfile_name_offset(pg_stop_backup());
        </entry>
       </row>
 
+      <row>
+       <entry id="pg-logical-emit-message-text">
+        <indexterm>
+         <primary>pg_logical_emit_message</primary>
+        </indexterm>
+        <literal><function>pg_logical_emit_message(<parameter>transactional</parameter> <type>bool</type>, <parameter>prefix</parameter> <type>text</type>, <parameter>content</parameter> <type>text</type>)</function></literal>
+       </entry>
+       <entry>
+        void
+       </entry>
+       <entry>
+        Write text logical decoding message. This can be used to pass generic
+        messages to logical decoding plugins through WAL. The parameter
+        <parameter>transactional</parameter> specifies if the message should
+        be part of current transaction or if it should be written immediately
+        and decoded as soon as the logical decoding reads the record. The
+        <parameter>prefix</parameter> is textual prefix used by the logical
+        decoding plugins to easily recognize interesting messages for them.
+        The <parameter>content</parameter> is the text of the message.
+       </entry>
+      </row>
+
+      <row>
+       <entry id="pg-logical-emit-message-bytea">
+        <indexterm>
+         <primary>>pg_logical_emit_message</primary>
+        </indexterm>
+        <literal><function>>pg_logical_emit_message(<parameter>transactional</parameter> <type>bool</type>, <parameter>prefix</parameter> <type>text</type>, <parameter>content</parameter> <type>bytea</type>)</function></literal>
+       </entry>
+       <entry>
+        void
+       </entry>
+       <entry>
+        Write binary logical decoding message. This can be used to pass generic
+        messages to logical decoding plugins through WAL. The parameter
+        <parameter>transactional</parameter> specifies if the message should
+        be part of current transaction or if it should be written immediately
+        and decoded as soon as the logical decoding reads the record. The
+        <parameter>prefix</parameter> is textual prefix used by the logical
+        decoding plugins to easily recognize interesting messages for them.
+        The <parameter>content</parameter> is the binary content of the
+        message.
+       </entry>
+      </row>
+
      </tbody>
     </tgroup>
    </table>
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index e841348..93ffcfb 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -363,6 +363,7 @@ typedef struct OutputPluginCallbacks
     LogicalDecodeBeginCB begin_cb;
     LogicalDecodeChangeCB change_cb;
     LogicalDecodeCommitCB commit_cb;
+    LogicalDecodeMessageCB message_cb;
     LogicalDecodeFilterByOriginCB filter_by_origin_cb;
     LogicalDecodeShutdownCB shutdown_cb;
 } OutputPluginCallbacks;
@@ -602,6 +603,42 @@ typedef bool (*LogicalDecodeFilterByOriginCB) (
        more efficient.
      </para>
      </sect3>
+
+    <sect3 id="logicaldecoding-output-plugin-message">
+     <title>Generic Message Callback</title>
+
+     <para>
+      The optional <function>message_cb</function> callback is called whenever
+      a logical decoding message has been decoded.
+<programlisting>
+typedef void (*LogicalDecodeMessageCB) (
+    struct LogicalDecodingContext *,
+    ReorderBufferTXN *txn,
+    XLogRecPtr message_lsn,
+    bool transactional,
+    const char *prefix,
+    Size message_size,
+    const char *message
+);
+</programlisting>
+      The <parameter>ctx</parameter> and <parameter>txn</parameter> parameters
+      have the same contents as for the <function>begin_cb</function> with the
+      difference that <parameter>txn</parameter> is null for non-transactional
+      messages. The <parameter>lsn</parameter> has WAL position of the message.
+      The <parameter>transactional</parameter> says if he message was sent as
+      transactional or not. The <parameter>prefix</parameter> is arbitrary
+      textual prefix which can be used for identifying interesting messages
+      for the current plugin. And finally the <parameter>message</parameter>
+      parameter holds the actual message of <parameter>message_size</parameter>
+      size.
+     </para>
+     <para>
+      Extra care should be taken to ensure that the prefix the output plugin
+      considers interesting is unique. Using name of the extension or the
+      output plugin itself is often a good choice.
+     </para>
+    </sect3>
+
    </sect2>
 
    <sect2 id="logicaldecoding-output-plugin-output">
diff --git a/src/backend/access/rmgrdesc/Makefile b/src/backend/access/rmgrdesc/Makefile
index c72a1f2..723b4d8 100644
--- a/src/backend/access/rmgrdesc/Makefile
+++ b/src/backend/access/rmgrdesc/Makefile
@@ -9,8 +9,8 @@ top_builddir = ../../../..
 include $(top_builddir)/src/Makefile.global
 
 OBJS = brindesc.o clogdesc.o committsdesc.o dbasedesc.o gindesc.o gistdesc.o \
-	   hashdesc.o heapdesc.o mxactdesc.o nbtdesc.o relmapdesc.o \
-	   replorigindesc.o seqdesc.o smgrdesc.o spgdesc.o \
+	   hashdesc.o heapdesc.o logicalmsgdesc.o mxactdesc.o nbtdesc.o \
+	   relmapdesc.o replorigindesc.o seqdesc.o smgrdesc.o spgdesc.o \
 	   standbydesc.o tblspcdesc.o xactdesc.o xlogdesc.o
 
 include $(top_srcdir)/src/backend/common.mk
diff --git a/src/backend/access/rmgrdesc/logicalmsgdesc.c b/src/backend/access/rmgrdesc/logicalmsgdesc.c
new file mode 100644
index 0000000..e5e84dd
--- /dev/null
+++ b/src/backend/access/rmgrdesc/logicalmsgdesc.c
@@ -0,0 +1,41 @@
+/*-------------------------------------------------------------------------
+ *
+ * logicalmsgdesc.c
+ *	  rmgr descriptor routines for replication/logical/message.c
+ *
+ * Portions Copyright (c) 2015-2016, PostgreSQL Global Development Group
+ *
+ *
+ * IDENTIFICATION
+ *	  src/backend/access/rmgrdesc/logicalmsgdesc.c
+ *
+ *-------------------------------------------------------------------------
+ */
+#include "postgres.h"
+
+#include "replication/message.h"
+
+void
+logicalmsg_desc(StringInfo buf, XLogReaderState *record)
+{
+	char	   *rec = XLogRecGetData(record);
+	uint8		info = XLogRecGetInfo(record) & ~XLR_INFO_MASK;
+
+	if (info == XLOG_LOGICAL_MESSAGE)
+	{
+		xl_logical_message *xlrec = (xl_logical_message *) rec;
+
+		appendStringInfo(buf, "%s message size %zu bytes",
+				   xlrec->transactional ? "transactional" : "nontransactional",
+						 xlrec->message_size);
+	}
+}
+
+const char *
+logicalmsg_identify(uint8 info)
+{
+	if (info & ~XLR_INFO_MASK == XLOG_LOGICAL_MESSAGE)
+		return "MESSAGE";
+
+	return NULL;
+}
diff --git a/src/backend/access/transam/rmgr.c b/src/backend/access/transam/rmgr.c
index 7c4d773..1a42121 100644
--- a/src/backend/access/transam/rmgr.c
+++ b/src/backend/access/transam/rmgr.c
@@ -23,6 +23,7 @@
 #include "commands/dbcommands_xlog.h"
 #include "commands/sequence.h"
 #include "commands/tablespace.h"
+#include "replication/message.h"
 #include "replication/origin.h"
 #include "storage/standby.h"
 #include "utils/relmapper.h"
diff --git a/src/backend/replication/logical/Makefile b/src/backend/replication/logical/Makefile
index 8adea13..1d7ca06 100644
--- a/src/backend/replication/logical/Makefile
+++ b/src/backend/replication/logical/Makefile
@@ -14,7 +14,7 @@ include $(top_builddir)/src/Makefile.global
 
 override CPPFLAGS := -I$(srcdir) $(CPPFLAGS)
 
-OBJS = decode.o logical.o logicalfuncs.o reorderbuffer.o origin.o \
+OBJS = decode.o logical.o logicalfuncs.o message.o origin.o reorderbuffer.o \
 	snapbuild.o
 
 include $(top_srcdir)/src/backend/common.mk
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index 88c3a49..368a2f6 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -39,6 +39,7 @@
 
 #include "replication/decode.h"
 #include "replication/logical.h"
+#include "replication/message.h"
 #include "replication/reorderbuffer.h"
 #include "replication/origin.h"
 #include "replication/snapbuild.h"
@@ -58,6 +59,7 @@ static void DecodeHeapOp(LogicalDecodingContext *ctx, XLogRecordBuffer *buf);
 static void DecodeHeap2Op(LogicalDecodingContext *ctx, XLogRecordBuffer *buf);
 static void DecodeXactOp(LogicalDecodingContext *ctx, XLogRecordBuffer *buf);
 static void DecodeStandbyOp(LogicalDecodingContext *ctx, XLogRecordBuffer *buf);
+static void DecodeLogicalMsgOp(LogicalDecodingContext *ctx, XLogRecordBuffer *buf);
 
 /* individual record(group)'s handlers */
 static void DecodeInsert(LogicalDecodingContext *ctx, XLogRecordBuffer *buf);
@@ -115,6 +117,10 @@ LogicalDecodingProcessRecord(LogicalDecodingContext *ctx, XLogReaderState *recor
 			DecodeHeapOp(ctx, &buf);
 			break;
 
+		case RM_LOGICALMSG_ID:
+			DecodeLogicalMsgOp(ctx, &buf);
+			break;
+
 			/*
 			 * Rmgrs irrelevant for logical decoding; they describe stuff not
 			 * represented in logical decoding. Add new rmgrs in rmgrlist.h's
@@ -431,6 +437,49 @@ DecodeHeapOp(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
 	}
 }
 
+/*
+ * Handle rmgr LOGICALMSG_ID records for DecodeRecordIntoReorderBuffer().
+ */
+static void
+DecodeLogicalMsgOp(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
+{
+	SnapBuild  *builder = ctx->snapshot_builder;
+	XLogReaderState *r = buf->record;
+	uint8		info = XLogRecGetInfo(r) & ~XLR_INFO_MASK;
+	xl_logical_message *message;
+
+	if (info != XLOG_LOGICAL_MESSAGE)
+		elog(ERROR, "unexpected RM_LOGICALMSG_ID record type: %u", info);
+
+	message = (xl_logical_message *) XLogRecGetData(r);
+
+	if (message->transactional)
+	{
+		if (!SnapBuildProcessChange(builder, XLogRecGetXid(r), buf->origptr))
+			return;
+
+		ReorderBufferQueueMessage(ctx->reorder, XLogRecGetXid(r),
+								  buf->endptr,
+								  message->message, /* first part of message is prefix */
+								  message->message_size,
+								  message->message + message->prefix_size);
+	}
+	else if (SnapBuildCurrentState(builder) == SNAPBUILD_CONSISTENT &&
+			 !SnapBuildXactNeedsSkip(builder, buf->origptr))
+	{
+		volatile Snapshot	snapshot_now;
+		ReorderBuffer	   *rb = ctx->reorder;
+
+		/* setup snapshot to allow catalog access */
+		snapshot_now = SnapBuildGetOrBuildSnapshot(builder, XLogRecGetXid(r));
+		SetupHistoricSnapshot(snapshot_now, NULL);
+		rb->message(rb, NULL, buf->origptr, false, message->message,
+					message->message_size,
+					message->message + message->prefix_size);
+		TeardownHistoricSnapshot(false);
+	}
+}
+
 static inline bool
 FilterByOrigin(LogicalDecodingContext *ctx, RepOriginId origin_id)
 {
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index 2e6d3f9..3974cd4 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -62,6 +62,9 @@ static void commit_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
 				  XLogRecPtr commit_lsn);
 static void change_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
 				  Relation relation, ReorderBufferChange *change);
+static void message_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
+				  XLogRecPtr message_lsn, bool transactional,
+				  const char *prefix, Size sz, const char *message);
 
 static void LoadOutputPlugin(OutputPluginCallbacks *callbacks, char *plugin);
 
@@ -178,6 +181,7 @@ StartupDecodingContext(List *output_plugin_options,
 	ctx->reorder->begin = begin_cb_wrapper;
 	ctx->reorder->apply_change = change_cb_wrapper;
 	ctx->reorder->commit = commit_cb_wrapper;
+	ctx->reorder->message = message_cb_wrapper;
 
 	ctx->out = makeStringInfo();
 	ctx->prepare_write = prepare_write;
@@ -702,6 +706,40 @@ filter_by_origin_cb_wrapper(LogicalDecodingContext *ctx, RepOriginId origin_id)
 	return ret;
 }
 
+static void message_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
+							   XLogRecPtr message_lsn,
+							   bool transactional, const char *prefix,
+							   Size sz, const char *message)
+{
+	LogicalDecodingContext *ctx = cache->private_data;
+	LogicalErrorCallbackState state;
+	ErrorContextCallback errcallback;
+
+	if (ctx->callbacks.message_cb == NULL)
+		return;
+
+	/* Push callback + info on the error context stack */
+	state.ctx = ctx;
+	state.callback_name = "message";
+	state.report_location = message_lsn;
+	errcallback.callback = output_plugin_error_callback;
+	errcallback.arg = (void *) &state;
+	errcallback.previous = error_context_stack;
+	error_context_stack = &errcallback;
+
+	/* set output state */
+	ctx->accept_writes = true;
+	ctx->write_xid = txn != NULL ? txn->xid : InvalidTransactionId;
+	ctx->write_location = message_lsn;
+
+	/* do the actual work: call callback */
+	ctx->callbacks.message_cb(ctx, txn, message_lsn, transactional,
+							  prefix, sz, message);
+
+	/* Pop the error context stack */
+	error_context_stack = errcallback.previous;
+}
+
 /*
  * Set the required catalog xmin horizon for historic snapshots in the current
  * replication slot.
diff --git a/src/backend/replication/logical/logicalfuncs.c b/src/backend/replication/logical/logicalfuncs.c
index f789fc1..fe22daa 100644
--- a/src/backend/replication/logical/logicalfuncs.c
+++ b/src/backend/replication/logical/logicalfuncs.c
@@ -24,6 +24,8 @@
 #include "access/xlog_internal.h"
 #include "access/xlogutils.h"
 
+#include "access/xact.h"
+
 #include "catalog/pg_type.h"
 
 #include "nodes/makefuncs.h"
@@ -41,6 +43,7 @@
 #include "replication/decode.h"
 #include "replication/logical.h"
 #include "replication/logicalfuncs.h"
+#include "replication/message.h"
 
 #include "storage/fd.h"
 
@@ -363,3 +366,27 @@ pg_logical_slot_peek_binary_changes(PG_FUNCTION_ARGS)
 {
 	return pg_logical_slot_get_changes_guts(fcinfo, false, true);
 }
+
+
+/*
+ * SQL function returning the changestream in binary, only peeking ahead.
+ */
+Datum
+pg_logical_emit_message_bytea(PG_FUNCTION_ARGS)
+{
+	bool		transactional = PG_GETARG_BOOL(0);
+	char	   *prefix = text_to_cstring(PG_GETARG_TEXT_PP(1));
+	bytea	   *data = PG_GETARG_BYTEA_PP(2);
+	XLogRecPtr	lsn;
+
+	lsn = LogLogicalMessage(prefix, VARDATA_ANY(data), VARSIZE_ANY_EXHDR(data),
+							transactional);
+	PG_RETURN_LSN(lsn);
+}
+
+Datum
+pg_logical_emit_message_text(PG_FUNCTION_ARGS)
+{
+	/* bytea and text are compatible */
+	return pg_logical_emit_message_bytea(fcinfo);
+}
diff --git a/src/backend/replication/logical/message.c b/src/backend/replication/logical/message.c
new file mode 100644
index 0000000..214be45
--- /dev/null
+++ b/src/backend/replication/logical/message.c
@@ -0,0 +1,87 @@
+/*-------------------------------------------------------------------------
+ *
+ * message.c
+ *	  Generic logical messages.
+ *
+ * Copyright (c) 2013-2016, PostgreSQL Global Development Group
+ *
+ * IDENTIFICATION
+ *	  src/backend/replication/logical/message.c
+ *
+ * NOTES
+ *
+ * Generic logical messages allow XLOG logging of arbitrary binary blobs that
+ * get passed to the logical decoding plugin. In normal XLOG processing they
+ * are same as NOOP.
+ *
+ * These messages can be either transactional or non-transactional.
+ * Transactional messages are part of current transaction and will be sent to
+ * decoding plugin using in a same way as DML operations.
+ * Non-transactional messages are sent to the plugin at the time when the
+ * logical decoding reads them from XLOG.
+ *
+ * Every message carries prefix to avoid conflicts between different decoding
+ * plugins. The prefix has to be registered before the message using that
+ * prefix can be written to XLOG. The prefix can be registered exactly once to
+ * avoid situation where multiple third party extensions try to use same
+ * prefix.
+ *
+ * ---------------------------------------------------------------------------
+ */
+
+#include "postgres.h"
+
+#include "access/xact.h"
+
+#include "catalog/indexing.h"
+
+#include "nodes/execnodes.h"
+
+#include "replication/message.h"
+#include "replication/logical.h"
+
+#include "utils/memutils.h"
+
+/*
+ * Write logical decoding message into XLog.
+ */
+XLogRecPtr
+LogLogicalMessage(const char *prefix, const char *message, size_t size,
+				  bool transactional)
+{
+	xl_logical_message	xlrec;
+
+	/*
+	 * Force xid to be allocated if we're emitting a transactional message.
+	 */
+	if (transactional)
+	{
+		Assert(IsTransactionState());
+		GetCurrentTransactionId();
+	}
+
+	xlrec.transactional = transactional;
+	xlrec.prefix_size = strlen(prefix) + 1;
+	xlrec.message_size = size;
+
+	XLogBeginInsert();
+	XLogRegisterData((char *) &xlrec, SizeOfLogicalMessage);
+	XLogRegisterData((char *) prefix, xlrec.prefix_size);
+	XLogRegisterData((char *) message, size);
+
+	return XLogInsert(RM_LOGICALMSG_ID, XLOG_LOGICAL_MESSAGE);
+}
+
+/*
+ * Redo is basically just noop for logical decoding messages.
+ */
+void
+logicalmsg_redo(XLogReaderState *record)
+{
+	uint8		info = XLogRecGetInfo(record) & ~XLR_INFO_MASK;
+
+	if (info != XLOG_LOGICAL_MESSAGE)
+			elog(PANIC, "logicalmsg_redo: unknown op code %u", info);
+
+	/* This is only interesting for logical decoding, see decode.c. */
+}
diff --git a/src/backend/replication/logical/reorderbuffer.c b/src/backend/replication/logical/reorderbuffer.c
index 78acced..0312346 100644
--- a/src/backend/replication/logical/reorderbuffer.c
+++ b/src/backend/replication/logical/reorderbuffer.c
@@ -414,6 +414,14 @@ ReorderBufferReturnChange(ReorderBuffer *rb, ReorderBufferChange *change)
 				change->data.tp.oldtuple = NULL;
 			}
 			break;
+		case REORDER_BUFFER_CHANGE_MESSAGE:
+			if (change->data.msg.prefix != NULL)
+				pfree(change->data.msg.prefix);
+			change->data.msg.prefix = NULL;
+			if (change->data.msg.message != NULL)
+				pfree(change->data.msg.message);
+			change->data.msg.message = NULL;
+			break;
 		case REORDER_BUFFER_CHANGE_INTERNAL_SNAPSHOT:
 			if (change->data.snapshot)
 			{
@@ -599,6 +607,26 @@ ReorderBufferQueueChange(ReorderBuffer *rb, TransactionId xid, XLogRecPtr lsn,
 	ReorderBufferCheckSerializeTXN(rb, txn);
 }
 
+void
+ReorderBufferQueueMessage(ReorderBuffer *rb, TransactionId xid, XLogRecPtr lsn,
+						  const char *prefix, Size msg_sz, const char *msg)
+{
+	ReorderBufferChange *change;
+
+	Assert(xid != InvalidTransactionId);
+
+	change = ReorderBufferGetChange(rb);
+	change->action = REORDER_BUFFER_CHANGE_MESSAGE;
+	change->data.msg.transactional = true;
+	change->data.msg.prefix = pstrdup(prefix);
+	change->data.msg.message_size = msg_sz;
+	change->data.msg.message = palloc(msg_sz);
+	memcpy(change->data.msg.message, msg, msg_sz);
+
+	ReorderBufferQueueChange(rb, xid, lsn, change);
+}
+
+
 static void
 AssertTXNLsnOrder(ReorderBuffer *rb)
 {
@@ -1465,6 +1493,14 @@ ReorderBufferCommit(ReorderBuffer *rb, TransactionId xid,
 					specinsert = change;
 					break;
 
+				case REORDER_BUFFER_CHANGE_MESSAGE:
+					rb->message(rb, txn, change->lsn,
+								change->data.msg.transactional,
+								change->data.msg.prefix,
+								change->data.msg.message_size,
+								change->data.msg.message);
+					break;
+
 				case REORDER_BUFFER_CHANGE_INTERNAL_SNAPSHOT:
 					/* get rid of the old */
 					TeardownHistoricSnapshot(false);
@@ -2117,6 +2153,21 @@ ReorderBufferSerializeChange(ReorderBuffer *rb, ReorderBufferTXN *txn,
 				}
 				break;
 			}
+		case REORDER_BUFFER_CHANGE_MESSAGE:
+			{
+				char	   *data;
+				size_t		prefix_size = strlen(change->data.msg.prefix) + 1;
+
+				sz += prefix_size + change->data.msg.message_size;
+				ReorderBufferSerializeReserve(rb, sz);
+
+				data = ((char *) rb->outbuf) + sizeof(ReorderBufferDiskChange);
+				memcpy(data, change->data.msg.prefix,
+					   prefix_size);
+				memcpy(data + prefix_size, change->data.msg.message,
+					   change->data.msg.message_size);
+				break;
+			}
 		case REORDER_BUFFER_CHANGE_INTERNAL_SNAPSHOT:
 			{
 				Snapshot	snap;
@@ -2354,6 +2405,22 @@ ReorderBufferRestoreChange(ReorderBuffer *rb, ReorderBufferTXN *txn,
 				data += len;
 			}
 			break;
+		case REORDER_BUFFER_CHANGE_MESSAGE:
+			{
+				Size		message_size = change->data.msg.message_size;
+				/* prefix includes trailing zero */
+				Size		prefix_size = strlen(data) + 1;
+
+				change->data.msg.prefix = MemoryContextAlloc(rb->context,
+															 prefix_size);
+				memcpy(change->data.msg.prefix, data, prefix_size);
+				data += prefix_size;
+				change->data.msg.message = MemoryContextAlloc(rb->context,
+															  message_size);
+				memcpy(change->data.msg.message, data, message_size);
+				data += message_size;
+				break;
+			}
 		case REORDER_BUFFER_CHANGE_INTERNAL_SNAPSHOT:
 			{
 				Snapshot	oldsnap;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index ed823ec..d7829c3 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -605,6 +605,25 @@ SnapBuildExportSnapshot(SnapBuild *builder)
 }
 
 /*
+ * Ensure there is a snapshot and if not build one for current transaction.
+ */
+Snapshot
+SnapBuildGetOrBuildSnapshot(SnapBuild *builder, TransactionId xid)
+{
+	Assert(builder->state == SNAPBUILD_CONSISTENT);
+
+	/* only build a new snapshot if we don't have a prebuilt one */
+	if (builder->snapshot == NULL)
+	{
+		builder->snapshot = SnapBuildBuildSnapshot(builder, xid);
+		/* inrease refcount for the snapshot builder */
+		SnapBuildSnapIncRefcount(builder->snapshot);
+	}
+
+	return builder->snapshot;
+}
+
+/*
  * Reset a previously SnapBuildExportSnapshot()'ed snapshot if there is
  * any. Aborts the previously started transaction and resets the resource
  * owner back to its original value.
diff --git a/src/bin/pg_xlogdump/rmgrdesc.c b/src/bin/pg_xlogdump/rmgrdesc.c
index f9cd395..6ba7f22 100644
--- a/src/bin/pg_xlogdump/rmgrdesc.c
+++ b/src/bin/pg_xlogdump/rmgrdesc.c
@@ -25,6 +25,7 @@
 #include "commands/dbcommands_xlog.h"
 #include "commands/sequence.h"
 #include "commands/tablespace.h"
+#include "replication/message.h"
 #include "replication/origin.h"
 #include "rmgrdesc.h"
 #include "storage/standbydefs.h"
diff --git a/src/include/access/rmgrlist.h b/src/include/access/rmgrlist.h
index fab912d..35c242d 100644
--- a/src/include/access/rmgrlist.h
+++ b/src/include/access/rmgrlist.h
@@ -45,3 +45,4 @@ PG_RMGR(RM_SPGIST_ID, "SPGist", spg_redo, spg_desc, spg_identify, spg_xlog_start
 PG_RMGR(RM_BRIN_ID, "BRIN", brin_redo, brin_desc, brin_identify, NULL, NULL)
 PG_RMGR(RM_COMMIT_TS_ID, "CommitTs", commit_ts_redo, commit_ts_desc, commit_ts_identify, NULL, NULL)
 PG_RMGR(RM_REPLORIGIN_ID, "ReplicationOrigin", replorigin_redo, replorigin_desc, replorigin_identify, NULL, NULL)
+PG_RMGR(RM_LOGICALMSG_ID, "LogicalMessage", logicalmsg_redo, logicalmsg_desc, logicalmsg_identify, NULL, NULL)
diff --git a/src/include/catalog/pg_proc.h b/src/include/catalog/pg_proc.h
index 62b9125..ff722fe 100644
--- a/src/include/catalog/pg_proc.h
+++ b/src/include/catalog/pg_proc.h
@@ -5084,6 +5084,10 @@ DATA(insert OID = 3784 (  pg_logical_slot_peek_changes PGNSP PGUID 12 1000 1000
 DESCR("peek at changes from replication slot");
 DATA(insert OID = 3785 (  pg_logical_slot_peek_binary_changes PGNSP PGUID 12 1000 1000 25 0 f f f f f t v u 4 0 2249 "19 3220 23 1009" "{19,3220,23,1009,3220,28,17}" "{i,i,i,v,o,o,o}" "{slot_name,upto_lsn,upto_nchanges,options,location,xid,data}" _null_ _null_ pg_logical_slot_peek_binary_changes _null_ _null_ _null_ ));
 DESCR("peek at binary changes from replication slot");
+DATA(insert OID = 3577 (  pg_logical_emit_message PGNSP PGUID 12 1 0 0 0 f f f f f f v u 3 0 3220 "16 25 25" _null_ _null_ _null_ _null_ _null_ pg_logical_emit_message_text _null_ _null_ _null_ ));
+DESCR("emit a textual logical decoding message");
+DATA(insert OID = 3578 (  pg_logical_emit_message PGNSP PGUID 12 1 0 0 0 f f f f f f v u 3 0 3220 "16 25 17" _null_ _null_ _null_ _null_ _null_ pg_logical_emit_message_bytea _null_ _null_ _null_ ));
+DESCR("emit a binary logical decoding message");
 
 /* event triggers */
 DATA(insert OID = 3566 (  pg_event_trigger_dropped_objects		PGNSP PGUID 12 10 100 0 0 f f f f t t s s 0 0 2249 "" "{26,26,23,16,16,16,25,25,25,25,1009,1009}" "{o,o,o,o,o,o,o,o,o,o,o,o}" "{classid, objid, objsubid, original, normal, is_temporary, object_type, schema_name, object_name, object_identity, address_names, address_args}" _null_ _null_ pg_event_trigger_dropped_objects _null_ _null_ _null_ ));
diff --git a/src/include/replication/logicalfuncs.h b/src/include/replication/logicalfuncs.h
index c87a1df..5540414 100644
--- a/src/include/replication/logicalfuncs.h
+++ b/src/include/replication/logicalfuncs.h
@@ -21,4 +21,6 @@ extern Datum pg_logical_slot_get_binary_changes(PG_FUNCTION_ARGS);
 extern Datum pg_logical_slot_peek_changes(PG_FUNCTION_ARGS);
 extern Datum pg_logical_slot_peek_binary_changes(PG_FUNCTION_ARGS);
 
+extern Datum pg_logical_emit_message_bytea(PG_FUNCTION_ARGS);
+extern Datum pg_logical_emit_message_text(PG_FUNCTION_ARGS);
 #endif
diff --git a/src/include/replication/message.h b/src/include/replication/message.h
new file mode 100644
index 0000000..b1730c9
--- /dev/null
+++ b/src/include/replication/message.h
@@ -0,0 +1,41 @@
+/*-------------------------------------------------------------------------
+ * message.h
+ *	   Exports from replication/logical/message.c
+ *
+ * Copyright (c) 2013-2016, PostgreSQL Global Development Group
+ *
+ * src/include/replication/message.h
+ *-------------------------------------------------------------------------
+ */
+#ifndef PG_LOGICAL_MESSAGE_H
+#define PG_LOGICAL_MESSAGE_H
+
+#include "access/xlog.h"
+#include "access/xlogdefs.h"
+#include "access/xlogreader.h"
+
+/*
+ * Generic logical decoding message wal record.
+ */
+typedef struct xl_logical_message
+{
+	bool		transactional;					/* is message transactional? */
+	size_t		prefix_size;					/* length of prefix */
+	size_t		message_size;					/* size of the message */
+	char		message[FLEXIBLE_ARRAY_MEMBER];	/* message including the null
+												 * terminated prefx of length
+												 * prefix_size */
+} xl_logical_message;
+
+#define SizeOfLogicalMessage	(offsetof(xl_logical_message, message))
+
+extern XLogRecPtr LogLogicalMessage(const char *prefix, const char *message,
+									size_t size, bool transactional);
+
+/* RMGR API*/
+#define XLOG_LOGICAL_MESSAGE	0x00
+void		logicalmsg_redo(XLogReaderState *record);
+void		logicalmsg_desc(StringInfo buf, XLogReaderState *record);
+const char *logicalmsg_identify(uint8 info);
+
+#endif   /* PG_LOGICAL_MESSAGE_H */
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 577b12e..3a2ca98 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -74,6 +74,18 @@ typedef void (*LogicalDecodeCommitCB) (
 												   XLogRecPtr commit_lsn);
 
 /*
+ * Called for the generic logical decoding messages.
+ */
+typedef void (*LogicalDecodeMessageCB) (
+											 struct LogicalDecodingContext *,
+											 ReorderBufferTXN *txn,
+											 XLogRecPtr message_lsn,
+											 bool transactional,
+											 const char *prefix,
+											 Size message_size,
+											 const char *message);
+
+/*
  * Filter changes by origin.
  */
 typedef bool (*LogicalDecodeFilterByOriginCB) (
@@ -96,6 +108,7 @@ typedef struct OutputPluginCallbacks
 	LogicalDecodeBeginCB begin_cb;
 	LogicalDecodeChangeCB change_cb;
 	LogicalDecodeCommitCB commit_cb;
+	LogicalDecodeMessageCB message_cb;
 	LogicalDecodeFilterByOriginCB filter_by_origin_cb;
 	LogicalDecodeShutdownCB shutdown_cb;
 } OutputPluginCallbacks;
diff --git a/src/include/replication/reorderbuffer.h b/src/include/replication/reorderbuffer.h
index d33ea27..a3af5a6 100644
--- a/src/include/replication/reorderbuffer.h
+++ b/src/include/replication/reorderbuffer.h
@@ -51,6 +51,7 @@ enum ReorderBufferChangeType
 	REORDER_BUFFER_CHANGE_INSERT,
 	REORDER_BUFFER_CHANGE_UPDATE,
 	REORDER_BUFFER_CHANGE_DELETE,
+	REORDER_BUFFER_CHANGE_MESSAGE,
 	REORDER_BUFFER_CHANGE_INTERNAL_SNAPSHOT,
 	REORDER_BUFFER_CHANGE_INTERNAL_COMMAND_ID,
 	REORDER_BUFFER_CHANGE_INTERNAL_TUPLECID,
@@ -95,6 +96,14 @@ typedef struct ReorderBufferChange
 			ReorderBufferTupleBuf *newtuple;
 		}			tp;
 
+		struct
+		{
+			bool transactional;
+			char *prefix;
+			size_t message_size;
+			char *message;
+		} msg;
+
 		/* New snapshot, set when action == *_INTERNAL_SNAPSHOT */
 		Snapshot	snapshot;
 
@@ -271,6 +280,15 @@ typedef void (*ReorderBufferCommitCB) (
 												   ReorderBufferTXN *txn,
 												   XLogRecPtr commit_lsn);
 
+/* message callback signature */
+typedef void (*ReorderBufferMessageCB) (
+												   ReorderBuffer *rb,
+												   ReorderBufferTXN *txn,
+												   XLogRecPtr message_lsn,
+												   bool transactional,
+												   const char *prefix, Size sz,
+												   const char *message);
+
 struct ReorderBuffer
 {
 	/*
@@ -297,6 +315,7 @@ struct ReorderBuffer
 	ReorderBufferBeginCB begin;
 	ReorderBufferApplyChangeCB apply_change;
 	ReorderBufferCommitCB commit;
+	ReorderBufferMessageCB message;
 
 	/*
 	 * Pointer that will be passed untouched to the callbacks.
@@ -347,6 +366,8 @@ ReorderBufferChange *ReorderBufferGetChange(ReorderBuffer *);
 void		ReorderBufferReturnChange(ReorderBuffer *, ReorderBufferChange *);
 
 void		ReorderBufferQueueChange(ReorderBuffer *, TransactionId, XLogRecPtr lsn, ReorderBufferChange *);
+void		ReorderBufferQueueMessage(ReorderBuffer *, TransactionId, XLogRecPtr lsn,
+									  const char *prefix, Size msg_sz, const char *msg);
 void ReorderBufferCommit(ReorderBuffer *, TransactionId,
 					XLogRecPtr commit_lsn, XLogRecPtr end_lsn,
 	  TimestampTz commit_time, RepOriginId origin_id, XLogRecPtr origin_lsn);
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index 75955af..c4127a1 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -63,6 +63,8 @@ extern const char *SnapBuildExportSnapshot(SnapBuild *snapstate);
 extern void SnapBuildClearExportedSnapshot(void);
 
 extern SnapBuildState SnapBuildCurrentState(SnapBuild *snapstate);
+extern Snapshot SnapBuildGetOrBuildSnapshot(SnapBuild *builder,
+											TransactionId xid);
 
 extern bool SnapBuildXactNeedsSkip(SnapBuild *snapstate, XLogRecPtr ptr);
 
-- 
1.9.1

From f65b4d858067af520e853cafb4fdfd11b6b3fdc0 Mon Sep 17 00:00:00 2001
From: Petr Jelinek <pjmodos@pjmodos.net>
Date: Wed, 24 Feb 2016 17:02:36 +0100
Subject: [PATCH] Logical Decoding Messages

---
 contrib/test_decoding/Makefile                  |  2 +-
 contrib/test_decoding/expected/ddl.out          | 21 ++++--
 contrib/test_decoding/expected/messages.out     | 56 ++++++++++++++++
 contrib/test_decoding/sql/ddl.sql               |  3 +-
 contrib/test_decoding/sql/messages.sql          | 17 +++++
 contrib/test_decoding/test_decoding.c           | 19 ++++++
 doc/src/sgml/func.sgml                          | 45 +++++++++++++
 doc/src/sgml/logicaldecoding.sgml               | 37 +++++++++++
 src/backend/access/rmgrdesc/Makefile            |  4 +-
 src/backend/access/rmgrdesc/logicalmsgdesc.c    | 41 ++++++++++++
 src/backend/access/transam/rmgr.c               |  1 +
 src/backend/replication/logical/Makefile        |  2 +-
 src/backend/replication/logical/decode.c        | 49 ++++++++++++++
 src/backend/replication/logical/logical.c       | 38 +++++++++++
 src/backend/replication/logical/logicalfuncs.c  | 27 ++++++++
 src/backend/replication/logical/message.c       | 87 +++++++++++++++++++++++++
 src/backend/replication/logical/reorderbuffer.c | 67 +++++++++++++++++++
 src/backend/replication/logical/snapbuild.c     | 19 ++++++
 src/bin/pg_xlogdump/rmgrdesc.c                  |  1 +
 src/include/access/rmgrlist.h                   |  1 +
 src/include/catalog/pg_proc.h                   |  4 ++
 src/include/replication/logicalfuncs.h          |  2 +
 src/include/replication/message.h               | 41 ++++++++++++
 src/include/replication/output_plugin.h         | 13 ++++
 src/include/replication/reorderbuffer.h         | 21 ++++++
 src/include/replication/snapbuild.h             |  2 +
 26 files changed, 608 insertions(+), 12 deletions(-)
 create mode 100644 contrib/test_decoding/expected/messages.out
 create mode 100644 contrib/test_decoding/sql/messages.sql
 create mode 100644 src/backend/access/rmgrdesc/logicalmsgdesc.c
 create mode 100644 src/backend/replication/logical/message.c
 create mode 100644 src/include/replication/message.h

diff --git a/contrib/test_decoding/Makefile b/contrib/test_decoding/Makefile
index 200c43e..7568531 100644
--- a/contrib/test_decoding/Makefile
+++ b/contrib/test_decoding/Makefile
@@ -38,7 +38,7 @@ submake-test_decoding:
 	$(MAKE) -C $(top_builddir)/contrib/test_decoding
 
 REGRESSCHECKS=ddl xact rewrite toast permissions decoding_in_xact \
-	decoding_into_rel binary prepared replorigin time
+	decoding_into_rel binary prepared replorigin time messages
 
 regresscheck: | submake-regress submake-test_decoding temp-install
 	$(MKDIR_P) regression_output
diff --git a/contrib/test_decoding/expected/ddl.out b/contrib/test_decoding/expected/ddl.out
index 77719e8..32cd24d 100644
--- a/contrib/test_decoding/expected/ddl.out
+++ b/contrib/test_decoding/expected/ddl.out
@@ -220,11 +220,17 @@ SELECT data FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'inc
 (7 rows)
 
 /*
- * check that disk spooling works
+ * check that disk spooling works (also for logical messages)
  */
 BEGIN;
 CREATE TABLE tr_etoomuch (id serial primary key, data int);
 INSERT INTO tr_etoomuch(data) SELECT g.i FROM generate_series(1, 10234) g(i);
+SELECT 'tx logical msg' FROM pg_logical_emit_message(true, 'test', 'tx logical msg');
+    ?column?    
+----------------
+ tx logical msg
+(1 row)
+
 DELETE FROM tr_etoomuch WHERE id < 5000;
 UPDATE tr_etoomuch SET data = - data WHERE id > 5000;
 COMMIT;
@@ -233,12 +239,13 @@ SELECT count(*), min(data), max(data)
 FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'include-xids', '0', 'skip-empty-xacts', '1')
 GROUP BY substring(data, 1, 24)
 ORDER BY 1,2;
- count |                       min                       |                                  max                                   
--------+-------------------------------------------------+------------------------------------------------------------------------
-     1 | BEGIN                                           | BEGIN
-     1 | COMMIT                                          | COMMIT
- 20467 | table public.tr_etoomuch: DELETE: id[integer]:1 | table public.tr_etoomuch: UPDATE: id[integer]:9999 data[integer]:-9999
-(3 rows)
+ count |                                  min                                  |                                  max                                   
+-------+-----------------------------------------------------------------------+------------------------------------------------------------------------
+     1 | BEGIN                                                                 | BEGIN
+     1 | COMMIT                                                                | COMMIT
+     1 | message: transactional: 1 prefix: test, sz: 14 content:tx logical msg | message: transactional: 1 prefix: test, sz: 14 content:tx logical msg
+ 20467 | table public.tr_etoomuch: DELETE: id[integer]:1                       | table public.tr_etoomuch: UPDATE: id[integer]:9999 data[integer]:-9999
+(4 rows)
 
 -- check updates of primary keys work correctly
 BEGIN;
diff --git a/contrib/test_decoding/expected/messages.out b/contrib/test_decoding/expected/messages.out
new file mode 100644
index 0000000..7fa8256
--- /dev/null
+++ b/contrib/test_decoding/expected/messages.out
@@ -0,0 +1,56 @@
+-- predictability
+SET synchronous_commit = on;
+SELECT 'init' FROM pg_create_logical_replication_slot('regression_slot', 'test_decoding');
+ ?column? 
+----------
+ init
+(1 row)
+
+SELECT 'msg1' FROM pg_logical_emit_message(true, 'test', 'msg1');
+ ?column? 
+----------
+ msg1
+(1 row)
+
+SELECT 'msg2' FROM pg_logical_emit_message(false, 'test', 'msg2');
+ ?column? 
+----------
+ msg2
+(1 row)
+
+BEGIN;
+SELECT 'msg3' FROM pg_logical_emit_message(true, 'test', 'msg3');
+ ?column? 
+----------
+ msg3
+(1 row)
+
+SELECT 'msg4' FROM pg_logical_emit_message(false, 'test', 'msg4');
+ ?column? 
+----------
+ msg4
+(1 row)
+
+SELECT 'msg5' FROM pg_logical_emit_message(true, 'test', 'msg5');
+ ?column? 
+----------
+ msg5
+(1 row)
+
+COMMIT;
+SELECT data FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'force-binary', '0', 'skip-empty-xacts', '1');
+                            data                            
+------------------------------------------------------------
+ message: transactional: 1 prefix: test, sz: 4 content:msg1
+ message: transactional: 0 prefix: test, sz: 4 content:msg2
+ message: transactional: 0 prefix: test, sz: 4 content:msg4
+ message: transactional: 1 prefix: test, sz: 4 content:msg3
+ message: transactional: 1 prefix: test, sz: 4 content:msg5
+(5 rows)
+
+SELECT 'init' FROM pg_drop_replication_slot('regression_slot');
+ ?column? 
+----------
+ init
+(1 row)
+
diff --git a/contrib/test_decoding/sql/ddl.sql b/contrib/test_decoding/sql/ddl.sql
index ad928ad..b1f7bf6 100644
--- a/contrib/test_decoding/sql/ddl.sql
+++ b/contrib/test_decoding/sql/ddl.sql
@@ -108,11 +108,12 @@ DELETE FROM tr_pkey;
 SELECT data FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'include-xids', '0', 'skip-empty-xacts', '1');
 
 /*
- * check that disk spooling works
+ * check that disk spooling works (also for logical messages)
  */
 BEGIN;
 CREATE TABLE tr_etoomuch (id serial primary key, data int);
 INSERT INTO tr_etoomuch(data) SELECT g.i FROM generate_series(1, 10234) g(i);
+SELECT 'tx logical msg' FROM pg_logical_emit_message(true, 'test', 'tx logical msg');
 DELETE FROM tr_etoomuch WHERE id < 5000;
 UPDATE tr_etoomuch SET data = - data WHERE id > 5000;
 COMMIT;
diff --git a/contrib/test_decoding/sql/messages.sql b/contrib/test_decoding/sql/messages.sql
new file mode 100644
index 0000000..8744eb6
--- /dev/null
+++ b/contrib/test_decoding/sql/messages.sql
@@ -0,0 +1,17 @@
+-- predictability
+SET synchronous_commit = on;
+
+SELECT 'init' FROM pg_create_logical_replication_slot('regression_slot', 'test_decoding');
+
+SELECT 'msg1' FROM pg_logical_emit_message(true, 'test', 'msg1');
+SELECT 'msg2' FROM pg_logical_emit_message(false, 'test', 'msg2');
+
+BEGIN;
+SELECT 'msg3' FROM pg_logical_emit_message(true, 'test', 'msg3');
+SELECT 'msg4' FROM pg_logical_emit_message(false, 'test', 'msg4');
+SELECT 'msg5' FROM pg_logical_emit_message(true, 'test', 'msg5');
+COMMIT;
+
+SELECT data FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'force-binary', '0', 'skip-empty-xacts', '1');
+
+SELECT 'init' FROM pg_drop_replication_slot('regression_slot');
diff --git a/contrib/test_decoding/test_decoding.c b/contrib/test_decoding/test_decoding.c
index 4cf808f..6395ffd 100644
--- a/contrib/test_decoding/test_decoding.c
+++ b/contrib/test_decoding/test_decoding.c
@@ -21,6 +21,7 @@
 
 #include "replication/output_plugin.h"
 #include "replication/logical.h"
+#include "replication/message.h"
 #include "replication/origin.h"
 
 #include "utils/builtins.h"
@@ -63,6 +64,10 @@ static void pg_decode_change(LogicalDecodingContext *ctx,
 				 ReorderBufferChange *change);
 static bool pg_decode_filter(LogicalDecodingContext *ctx,
 				 RepOriginId origin_id);
+static void pg_decode_message(LogicalDecodingContext *ctx,
+							  ReorderBufferTXN *txn, XLogRecPtr message_lsn,
+							  bool transactional, const char *prefix,
+							  Size sz, const char *message);
 
 void
 _PG_init(void)
@@ -82,6 +87,7 @@ _PG_output_plugin_init(OutputPluginCallbacks *cb)
 	cb->commit_cb = pg_decode_commit_txn;
 	cb->filter_by_origin_cb = pg_decode_filter;
 	cb->shutdown_cb = pg_decode_shutdown;
+	cb->message_cb = pg_decode_message;
 }
 
 
@@ -471,3 +477,16 @@ pg_decode_change(LogicalDecodingContext *ctx, ReorderBufferTXN *txn,
 
 	OutputPluginWrite(ctx, true);
 }
+
+static void
+pg_decode_message(LogicalDecodingContext *ctx,
+				  ReorderBufferTXN *txn, XLogRecPtr lsn,
+				  bool transactional, const char *prefix,
+				  Size sz, const char *message)
+{
+	OutputPluginPrepareWrite(ctx, true);
+	appendStringInfo(ctx->out, "message: transactional: %d prefix: %s, sz: %zu content:",
+					 transactional, prefix, sz);
+	appendBinaryStringInfo(ctx->out, message, sz);
+	OutputPluginWrite(ctx, true);
+}
diff --git a/doc/src/sgml/func.sgml b/doc/src/sgml/func.sgml
index 4b5ee81..0f6bc20 100644
--- a/doc/src/sgml/func.sgml
+++ b/doc/src/sgml/func.sgml
@@ -18125,6 +18125,51 @@ postgres=# SELECT * FROM pg_xlogfile_name_offset(pg_stop_backup());
        </entry>
       </row>
 
+      <row>
+       <entry id="pg-logical-emit-message-text">
+        <indexterm>
+         <primary>pg_logical_emit_message</primary>
+        </indexterm>
+        <literal><function>pg_logical_emit_message(<parameter>transactional</parameter> <type>bool</type>, <parameter>prefix</parameter> <type>text</type>, <parameter>content</parameter> <type>text</type>)</function></literal>
+       </entry>
+       <entry>
+        void
+       </entry>
+       <entry>
+        Write text logical decoding message. This can be used to pass generic
+        messages to logical decoding plugins through WAL. The parameter
+        <parameter>transactional</parameter> specifies if the message should
+        be part of current transaction or if it should be written immediately
+        and decoded as soon as the logical decoding reads the record. The
+        <parameter>prefix</parameter> is textual prefix used by the logical
+        decoding plugins to easily recognize interesting messages for them.
+        The <parameter>content</parameter> is the text of the message.
+       </entry>
+      </row>
+
+      <row>
+       <entry id="pg-logical-emit-message-bytea">
+        <indexterm>
+         <primary>>pg_logical_emit_message</primary>
+        </indexterm>
+        <literal><function>>pg_logical_emit_message(<parameter>transactional</parameter> <type>bool</type>, <parameter>prefix</parameter> <type>text</type>, <parameter>content</parameter> <type>bytea</type>)</function></literal>
+       </entry>
+       <entry>
+        void
+       </entry>
+       <entry>
+        Write binary logical decoding message. This can be used to pass generic
+        messages to logical decoding plugins through WAL. The parameter
+        <parameter>transactional</parameter> specifies if the message should
+        be part of current transaction or if it should be written immediately
+        and decoded as soon as the logical decoding reads the record. The
+        <parameter>prefix</parameter> is textual prefix used by the logical
+        decoding plugins to easily recognize interesting messages for them.
+        The <parameter>content</parameter> is the binary content of the
+        message.
+       </entry>
+      </row>
+
      </tbody>
     </tgroup>
    </table>
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 45fdfeb..f4e4506 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -363,6 +363,7 @@ typedef struct OutputPluginCallbacks
     LogicalDecodeBeginCB begin_cb;
     LogicalDecodeChangeCB change_cb;
     LogicalDecodeCommitCB commit_cb;
+    LogicalDecodeMessageCB message_cb;
     LogicalDecodeFilterByOriginCB filter_by_origin_cb;
     LogicalDecodeShutdownCB shutdown_cb;
 } OutputPluginCallbacks;
@@ -602,6 +603,42 @@ typedef bool (*LogicalDecodeFilterByOriginCB) (
        more efficient.
      </para>
      </sect3>
+
+    <sect3 id="logicaldecoding-output-plugin-message">
+     <title>Generic Message Callback</title>
+
+     <para>
+      The optional <function>message_cb</function> callback is called whenever
+      a logical decoding message has been decoded.
+<programlisting>
+typedef void (*LogicalDecodeMessageCB) (
+    struct LogicalDecodingContext *,
+    ReorderBufferTXN *txn,
+    XLogRecPtr message_lsn,
+    bool transactional,
+    const char *prefix,
+    Size message_size,
+    const char *message
+);
+</programlisting>
+      The <parameter>ctx</parameter> and <parameter>txn</parameter> parameters
+      have the same contents as for the <function>begin_cb</function> with the
+      difference that <parameter>txn</parameter> is null for non-transactional
+      messages. The <parameter>lsn</parameter> has WAL position of the message.
+      The <parameter>transactional</parameter> says if he message was sent as
+      transactional or not. The <parameter>prefix</parameter> is arbitrary
+      textual prefix which can be used for identifying interesting messages
+      for the current plugin. And finally the <parameter>message</parameter>
+      parameter holds the actual message of <parameter>message_size</parameter>
+      size.
+     </para>
+     <para>
+      Extra care should be taken to ensure that the prefix the output plugin
+      considers interesting is unique. Using name of the extension or the
+      output plugin itself is often a good choice.
+     </para>
+    </sect3>
+
    </sect2>
 
    <sect2 id="logicaldecoding-output-plugin-output">
diff --git a/src/backend/access/rmgrdesc/Makefile b/src/backend/access/rmgrdesc/Makefile
index c72a1f2..723b4d8 100644
--- a/src/backend/access/rmgrdesc/Makefile
+++ b/src/backend/access/rmgrdesc/Makefile
@@ -9,8 +9,8 @@ top_builddir = ../../../..
 include $(top_builddir)/src/Makefile.global
 
 OBJS = brindesc.o clogdesc.o committsdesc.o dbasedesc.o gindesc.o gistdesc.o \
-	   hashdesc.o heapdesc.o mxactdesc.o nbtdesc.o relmapdesc.o \
-	   replorigindesc.o seqdesc.o smgrdesc.o spgdesc.o \
+	   hashdesc.o heapdesc.o logicalmsgdesc.o mxactdesc.o nbtdesc.o \
+	   relmapdesc.o replorigindesc.o seqdesc.o smgrdesc.o spgdesc.o \
 	   standbydesc.o tblspcdesc.o xactdesc.o xlogdesc.o
 
 include $(top_srcdir)/src/backend/common.mk
diff --git a/src/backend/access/rmgrdesc/logicalmsgdesc.c b/src/backend/access/rmgrdesc/logicalmsgdesc.c
new file mode 100644
index 0000000..b194e14
--- /dev/null
+++ b/src/backend/access/rmgrdesc/logicalmsgdesc.c
@@ -0,0 +1,41 @@
+/*-------------------------------------------------------------------------
+ *
+ * logicalmsgdesc.c
+ *	  rmgr descriptor routines for replication/logical/message.c
+ *
+ * Portions Copyright (c) 2015-2016, PostgreSQL Global Development Group
+ *
+ *
+ * IDENTIFICATION
+ *	  src/backend/access/rmgrdesc/logicalmsgdesc.c
+ *
+ *-------------------------------------------------------------------------
+ */
+#include "postgres.h"
+
+#include "replication/message.h"
+
+void
+logicalmsg_desc(StringInfo buf, XLogReaderState *record)
+{
+	char	   *rec = XLogRecGetData(record);
+	uint8		info = XLogRecGetInfo(record) & ~XLR_INFO_MASK;
+
+	if (info == XLOG_LOGICAL_MESSAGE)
+	{
+		xl_logical_message *xlrec = (xl_logical_message *) rec;
+
+		appendStringInfo(buf, "%s message size %zu bytes",
+				   xlrec->transactional ? "transactional" : "nontransactional",
+						 xlrec->message_size);
+	}
+}
+
+const char *
+logicalmsg_identify(uint8 info)
+{
+	if ((info & ~XLR_INFO_MASK) == XLOG_LOGICAL_MESSAGE)
+		return "MESSAGE";
+
+	return NULL;
+}
diff --git a/src/backend/access/transam/rmgr.c b/src/backend/access/transam/rmgr.c
index 7c4d773..1a42121 100644
--- a/src/backend/access/transam/rmgr.c
+++ b/src/backend/access/transam/rmgr.c
@@ -23,6 +23,7 @@
 #include "commands/dbcommands_xlog.h"
 #include "commands/sequence.h"
 #include "commands/tablespace.h"
+#include "replication/message.h"
 #include "replication/origin.h"
 #include "storage/standby.h"
 #include "utils/relmapper.h"
diff --git a/src/backend/replication/logical/Makefile b/src/backend/replication/logical/Makefile
index 8adea13..1d7ca06 100644
--- a/src/backend/replication/logical/Makefile
+++ b/src/backend/replication/logical/Makefile
@@ -14,7 +14,7 @@ include $(top_builddir)/src/Makefile.global
 
 override CPPFLAGS := -I$(srcdir) $(CPPFLAGS)
 
-OBJS = decode.o logical.o logicalfuncs.o reorderbuffer.o origin.o \
+OBJS = decode.o logical.o logicalfuncs.o message.o origin.o reorderbuffer.o \
 	snapbuild.o
 
 include $(top_srcdir)/src/backend/common.mk
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index 13af485..b945d35 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -39,6 +39,7 @@
 
 #include "replication/decode.h"
 #include "replication/logical.h"
+#include "replication/message.h"
 #include "replication/reorderbuffer.h"
 #include "replication/origin.h"
 #include "replication/snapbuild.h"
@@ -58,6 +59,7 @@ static void DecodeHeapOp(LogicalDecodingContext *ctx, XLogRecordBuffer *buf);
 static void DecodeHeap2Op(LogicalDecodingContext *ctx, XLogRecordBuffer *buf);
 static void DecodeXactOp(LogicalDecodingContext *ctx, XLogRecordBuffer *buf);
 static void DecodeStandbyOp(LogicalDecodingContext *ctx, XLogRecordBuffer *buf);
+static void DecodeLogicalMsgOp(LogicalDecodingContext *ctx, XLogRecordBuffer *buf);
 
 /* individual record(group)'s handlers */
 static void DecodeInsert(LogicalDecodingContext *ctx, XLogRecordBuffer *buf);
@@ -123,6 +125,10 @@ LogicalDecodingProcessRecord(LogicalDecodingContext *ctx, XLogReaderState *recor
 			DecodeHeapOp(ctx, &buf);
 			break;
 
+		case RM_LOGICALMSG_ID:
+			DecodeLogicalMsgOp(ctx, &buf);
+			break;
+
 			/*
 			 * Rmgrs irrelevant for logical decoding; they describe stuff not
 			 * represented in logical decoding. Add new rmgrs in rmgrlist.h's
@@ -457,6 +463,49 @@ DecodeHeapOp(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
 	}
 }
 
+/*
+ * Handle rmgr LOGICALMSG_ID records for DecodeRecordIntoReorderBuffer().
+ */
+static void
+DecodeLogicalMsgOp(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
+{
+	SnapBuild  *builder = ctx->snapshot_builder;
+	XLogReaderState *r = buf->record;
+	uint8		info = XLogRecGetInfo(r) & ~XLR_INFO_MASK;
+	xl_logical_message *message;
+
+	if (info != XLOG_LOGICAL_MESSAGE)
+		elog(ERROR, "unexpected RM_LOGICALMSG_ID record type: %u", info);
+
+	message = (xl_logical_message *) XLogRecGetData(r);
+
+	if (message->transactional)
+	{
+		if (!SnapBuildProcessChange(builder, XLogRecGetXid(r), buf->origptr))
+			return;
+
+		ReorderBufferQueueMessage(ctx->reorder, XLogRecGetXid(r),
+								  buf->endptr,
+								  message->message, /* first part of message is prefix */
+								  message->message_size,
+								  message->message + message->prefix_size);
+	}
+	else if (SnapBuildCurrentState(builder) == SNAPBUILD_CONSISTENT &&
+			 !SnapBuildXactNeedsSkip(builder, buf->origptr))
+	{
+		volatile Snapshot	snapshot_now;
+		ReorderBuffer	   *rb = ctx->reorder;
+
+		/* setup snapshot to allow catalog access */
+		snapshot_now = SnapBuildGetOrBuildSnapshot(builder, XLogRecGetXid(r));
+		SetupHistoricSnapshot(snapshot_now, NULL);
+		rb->message(rb, NULL, buf->origptr, false, message->message,
+					message->message_size,
+					message->message + message->prefix_size);
+		TeardownHistoricSnapshot(false);
+	}
+}
+
 static inline bool
 FilterByOrigin(LogicalDecodingContext *ctx, RepOriginId origin_id)
 {
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index 2e6d3f9..7a34251 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -62,6 +62,9 @@ static void commit_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
 				  XLogRecPtr commit_lsn);
 static void change_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
 				  Relation relation, ReorderBufferChange *change);
+static void message_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
+				  XLogRecPtr message_lsn, bool transactional,
+				  const char *prefix, Size sz, const char *message);
 
 static void LoadOutputPlugin(OutputPluginCallbacks *callbacks, char *plugin);
 
@@ -178,6 +181,7 @@ StartupDecodingContext(List *output_plugin_options,
 	ctx->reorder->begin = begin_cb_wrapper;
 	ctx->reorder->apply_change = change_cb_wrapper;
 	ctx->reorder->commit = commit_cb_wrapper;
+	ctx->reorder->message = message_cb_wrapper;
 
 	ctx->out = makeStringInfo();
 	ctx->prepare_write = prepare_write;
@@ -702,6 +706,40 @@ filter_by_origin_cb_wrapper(LogicalDecodingContext *ctx, RepOriginId origin_id)
 	return ret;
 }
 
+static void
+message_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
+				   XLogRecPtr message_lsn, bool transactional,
+				   const char *prefix, Size sz, const char *message)
+{
+	LogicalDecodingContext *ctx = cache->private_data;
+	LogicalErrorCallbackState state;
+	ErrorContextCallback errcallback;
+
+	if (ctx->callbacks.message_cb == NULL)
+		return;
+
+	/* Push callback + info on the error context stack */
+	state.ctx = ctx;
+	state.callback_name = "message";
+	state.report_location = message_lsn;
+	errcallback.callback = output_plugin_error_callback;
+	errcallback.arg = (void *) &state;
+	errcallback.previous = error_context_stack;
+	error_context_stack = &errcallback;
+
+	/* set output state */
+	ctx->accept_writes = true;
+	ctx->write_xid = txn != NULL ? txn->xid : InvalidTransactionId;
+	ctx->write_location = message_lsn;
+
+	/* do the actual work: call callback */
+	ctx->callbacks.message_cb(ctx, txn, message_lsn, transactional,
+							  prefix, sz, message);
+
+	/* Pop the error context stack */
+	error_context_stack = errcallback.previous;
+}
+
 /*
  * Set the required catalog xmin horizon for historic snapshots in the current
  * replication slot.
diff --git a/src/backend/replication/logical/logicalfuncs.c b/src/backend/replication/logical/logicalfuncs.c
index f789fc1..fe22daa 100644
--- a/src/backend/replication/logical/logicalfuncs.c
+++ b/src/backend/replication/logical/logicalfuncs.c
@@ -24,6 +24,8 @@
 #include "access/xlog_internal.h"
 #include "access/xlogutils.h"
 
+#include "access/xact.h"
+
 #include "catalog/pg_type.h"
 
 #include "nodes/makefuncs.h"
@@ -41,6 +43,7 @@
 #include "replication/decode.h"
 #include "replication/logical.h"
 #include "replication/logicalfuncs.h"
+#include "replication/message.h"
 
 #include "storage/fd.h"
 
@@ -363,3 +366,27 @@ pg_logical_slot_peek_binary_changes(PG_FUNCTION_ARGS)
 {
 	return pg_logical_slot_get_changes_guts(fcinfo, false, true);
 }
+
+
+/*
+ * SQL function returning the changestream in binary, only peeking ahead.
+ */
+Datum
+pg_logical_emit_message_bytea(PG_FUNCTION_ARGS)
+{
+	bool		transactional = PG_GETARG_BOOL(0);
+	char	   *prefix = text_to_cstring(PG_GETARG_TEXT_PP(1));
+	bytea	   *data = PG_GETARG_BYTEA_PP(2);
+	XLogRecPtr	lsn;
+
+	lsn = LogLogicalMessage(prefix, VARDATA_ANY(data), VARSIZE_ANY_EXHDR(data),
+							transactional);
+	PG_RETURN_LSN(lsn);
+}
+
+Datum
+pg_logical_emit_message_text(PG_FUNCTION_ARGS)
+{
+	/* bytea and text are compatible */
+	return pg_logical_emit_message_bytea(fcinfo);
+}
diff --git a/src/backend/replication/logical/message.c b/src/backend/replication/logical/message.c
new file mode 100644
index 0000000..214be45
--- /dev/null
+++ b/src/backend/replication/logical/message.c
@@ -0,0 +1,87 @@
+/*-------------------------------------------------------------------------
+ *
+ * message.c
+ *	  Generic logical messages.
+ *
+ * Copyright (c) 2013-2016, PostgreSQL Global Development Group
+ *
+ * IDENTIFICATION
+ *	  src/backend/replication/logical/message.c
+ *
+ * NOTES
+ *
+ * Generic logical messages allow XLOG logging of arbitrary binary blobs that
+ * get passed to the logical decoding plugin. In normal XLOG processing they
+ * are same as NOOP.
+ *
+ * These messages can be either transactional or non-transactional.
+ * Transactional messages are part of current transaction and will be sent to
+ * decoding plugin using in a same way as DML operations.
+ * Non-transactional messages are sent to the plugin at the time when the
+ * logical decoding reads them from XLOG.
+ *
+ * Every message carries prefix to avoid conflicts between different decoding
+ * plugins. The prefix has to be registered before the message using that
+ * prefix can be written to XLOG. The prefix can be registered exactly once to
+ * avoid situation where multiple third party extensions try to use same
+ * prefix.
+ *
+ * ---------------------------------------------------------------------------
+ */
+
+#include "postgres.h"
+
+#include "access/xact.h"
+
+#include "catalog/indexing.h"
+
+#include "nodes/execnodes.h"
+
+#include "replication/message.h"
+#include "replication/logical.h"
+
+#include "utils/memutils.h"
+
+/*
+ * Write logical decoding message into XLog.
+ */
+XLogRecPtr
+LogLogicalMessage(const char *prefix, const char *message, size_t size,
+				  bool transactional)
+{
+	xl_logical_message	xlrec;
+
+	/*
+	 * Force xid to be allocated if we're emitting a transactional message.
+	 */
+	if (transactional)
+	{
+		Assert(IsTransactionState());
+		GetCurrentTransactionId();
+	}
+
+	xlrec.transactional = transactional;
+	xlrec.prefix_size = strlen(prefix) + 1;
+	xlrec.message_size = size;
+
+	XLogBeginInsert();
+	XLogRegisterData((char *) &xlrec, SizeOfLogicalMessage);
+	XLogRegisterData((char *) prefix, xlrec.prefix_size);
+	XLogRegisterData((char *) message, size);
+
+	return XLogInsert(RM_LOGICALMSG_ID, XLOG_LOGICAL_MESSAGE);
+}
+
+/*
+ * Redo is basically just noop for logical decoding messages.
+ */
+void
+logicalmsg_redo(XLogReaderState *record)
+{
+	uint8		info = XLogRecGetInfo(record) & ~XLR_INFO_MASK;
+
+	if (info != XLOG_LOGICAL_MESSAGE)
+			elog(PANIC, "logicalmsg_redo: unknown op code %u", info);
+
+	/* This is only interesting for logical decoding, see decode.c. */
+}
diff --git a/src/backend/replication/logical/reorderbuffer.c b/src/backend/replication/logical/reorderbuffer.c
index f2b8f4b..bb6f438 100644
--- a/src/backend/replication/logical/reorderbuffer.c
+++ b/src/backend/replication/logical/reorderbuffer.c
@@ -414,6 +414,14 @@ ReorderBufferReturnChange(ReorderBuffer *rb, ReorderBufferChange *change)
 				change->data.tp.oldtuple = NULL;
 			}
 			break;
+		case REORDER_BUFFER_CHANGE_MESSAGE:
+			if (change->data.msg.prefix != NULL)
+				pfree(change->data.msg.prefix);
+			change->data.msg.prefix = NULL;
+			if (change->data.msg.message != NULL)
+				pfree(change->data.msg.message);
+			change->data.msg.message = NULL;
+			break;
 		case REORDER_BUFFER_CHANGE_INTERNAL_SNAPSHOT:
 			if (change->data.snapshot)
 			{
@@ -627,6 +635,26 @@ ReorderBufferQueueChange(ReorderBuffer *rb, TransactionId xid, XLogRecPtr lsn,
 	ReorderBufferCheckSerializeTXN(rb, txn);
 }
 
+void
+ReorderBufferQueueMessage(ReorderBuffer *rb, TransactionId xid, XLogRecPtr lsn,
+						  const char *prefix, Size msg_sz, const char *msg)
+{
+	ReorderBufferChange *change;
+
+	Assert(xid != InvalidTransactionId);
+
+	change = ReorderBufferGetChange(rb);
+	change->action = REORDER_BUFFER_CHANGE_MESSAGE;
+	change->data.msg.transactional = true;
+	change->data.msg.prefix = pstrdup(prefix);
+	change->data.msg.message_size = msg_sz;
+	change->data.msg.message = palloc(msg_sz);
+	memcpy(change->data.msg.message, msg, msg_sz);
+
+	ReorderBufferQueueChange(rb, xid, lsn, change);
+}
+
+
 static void
 AssertTXNLsnOrder(ReorderBuffer *rb)
 {
@@ -1493,6 +1521,14 @@ ReorderBufferCommit(ReorderBuffer *rb, TransactionId xid,
 					specinsert = change;
 					break;
 
+				case REORDER_BUFFER_CHANGE_MESSAGE:
+					rb->message(rb, txn, change->lsn,
+								change->data.msg.transactional,
+								change->data.msg.prefix,
+								change->data.msg.message_size,
+								change->data.msg.message);
+					break;
+
 				case REORDER_BUFFER_CHANGE_INTERNAL_SNAPSHOT:
 					/* get rid of the old */
 					TeardownHistoricSnapshot(false);
@@ -2159,6 +2195,21 @@ ReorderBufferSerializeChange(ReorderBuffer *rb, ReorderBufferTXN *txn,
 				}
 				break;
 			}
+		case REORDER_BUFFER_CHANGE_MESSAGE:
+			{
+				char	   *data;
+				size_t		prefix_size = strlen(change->data.msg.prefix) + 1;
+
+				sz += prefix_size + change->data.msg.message_size;
+				ReorderBufferSerializeReserve(rb, sz);
+
+				data = ((char *) rb->outbuf) + sizeof(ReorderBufferDiskChange);
+				memcpy(data, change->data.msg.prefix,
+					   prefix_size);
+				memcpy(data + prefix_size, change->data.msg.message,
+					   change->data.msg.message_size);
+				break;
+			}
 		case REORDER_BUFFER_CHANGE_INTERNAL_SNAPSHOT:
 			{
 				Snapshot	snap;
@@ -2415,6 +2466,22 @@ ReorderBufferRestoreChange(ReorderBuffer *rb, ReorderBufferTXN *txn,
 			}
 
 			break;
+		case REORDER_BUFFER_CHANGE_MESSAGE:
+			{
+				Size		message_size = change->data.msg.message_size;
+				/* prefix includes trailing zero */
+				Size		prefix_size = strlen(data) + 1;
+
+				change->data.msg.prefix = MemoryContextAlloc(rb->context,
+															 prefix_size);
+				memcpy(change->data.msg.prefix, data, prefix_size);
+				data += prefix_size;
+				change->data.msg.message = MemoryContextAlloc(rb->context,
+															  message_size);
+				memcpy(change->data.msg.message, data, message_size);
+				data += message_size;
+				break;
+			}
 		case REORDER_BUFFER_CHANGE_INTERNAL_SNAPSHOT:
 			{
 				Snapshot	oldsnap;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index 179b85a..b4dc617 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -605,6 +605,25 @@ SnapBuildExportSnapshot(SnapBuild *builder)
 }
 
 /*
+ * Ensure there is a snapshot and if not build one for current transaction.
+ */
+Snapshot
+SnapBuildGetOrBuildSnapshot(SnapBuild *builder, TransactionId xid)
+{
+	Assert(builder->state == SNAPBUILD_CONSISTENT);
+
+	/* only build a new snapshot if we don't have a prebuilt one */
+	if (builder->snapshot == NULL)
+	{
+		builder->snapshot = SnapBuildBuildSnapshot(builder, xid);
+		/* inrease refcount for the snapshot builder */
+		SnapBuildSnapIncRefcount(builder->snapshot);
+	}
+
+	return builder->snapshot;
+}
+
+/*
  * Reset a previously SnapBuildExportSnapshot()'ed snapshot if there is
  * any. Aborts the previously started transaction and resets the resource
  * owner back to its original value.
diff --git a/src/bin/pg_xlogdump/rmgrdesc.c b/src/bin/pg_xlogdump/rmgrdesc.c
index f9cd395..6ba7f22 100644
--- a/src/bin/pg_xlogdump/rmgrdesc.c
+++ b/src/bin/pg_xlogdump/rmgrdesc.c
@@ -25,6 +25,7 @@
 #include "commands/dbcommands_xlog.h"
 #include "commands/sequence.h"
 #include "commands/tablespace.h"
+#include "replication/message.h"
 #include "replication/origin.h"
 #include "rmgrdesc.h"
 #include "storage/standbydefs.h"
diff --git a/src/include/access/rmgrlist.h b/src/include/access/rmgrlist.h
index fab912d..35c242d 100644
--- a/src/include/access/rmgrlist.h
+++ b/src/include/access/rmgrlist.h
@@ -45,3 +45,4 @@ PG_RMGR(RM_SPGIST_ID, "SPGist", spg_redo, spg_desc, spg_identify, spg_xlog_start
 PG_RMGR(RM_BRIN_ID, "BRIN", brin_redo, brin_desc, brin_identify, NULL, NULL)
 PG_RMGR(RM_COMMIT_TS_ID, "CommitTs", commit_ts_redo, commit_ts_desc, commit_ts_identify, NULL, NULL)
 PG_RMGR(RM_REPLORIGIN_ID, "ReplicationOrigin", replorigin_redo, replorigin_desc, replorigin_identify, NULL, NULL)
+PG_RMGR(RM_LOGICALMSG_ID, "LogicalMessage", logicalmsg_redo, logicalmsg_desc, logicalmsg_identify, NULL, NULL)
diff --git a/src/include/catalog/pg_proc.h b/src/include/catalog/pg_proc.h
index a0f821a..bae5540 100644
--- a/src/include/catalog/pg_proc.h
+++ b/src/include/catalog/pg_proc.h
@@ -5095,6 +5095,10 @@ DATA(insert OID = 3784 (  pg_logical_slot_peek_changes PGNSP PGUID 12 1000 1000
 DESCR("peek at changes from replication slot");
 DATA(insert OID = 3785 (  pg_logical_slot_peek_binary_changes PGNSP PGUID 12 1000 1000 25 0 f f f f f t v u 4 0 2249 "19 3220 23 1009" "{19,3220,23,1009,3220,28,17}" "{i,i,i,v,o,o,o}" "{slot_name,upto_lsn,upto_nchanges,options,location,xid,data}" _null_ _null_ pg_logical_slot_peek_binary_changes _null_ _null_ _null_ ));
 DESCR("peek at binary changes from replication slot");
+DATA(insert OID = 3577 (  pg_logical_emit_message PGNSP PGUID 12 1 0 0 0 f f f f f f v u 3 0 3220 "16 25 25" _null_ _null_ _null_ _null_ _null_ pg_logical_emit_message_text _null_ _null_ _null_ ));
+DESCR("emit a textual logical decoding message");
+DATA(insert OID = 3578 (  pg_logical_emit_message PGNSP PGUID 12 1 0 0 0 f f f f f f v u 3 0 3220 "16 25 17" _null_ _null_ _null_ _null_ _null_ pg_logical_emit_message_bytea _null_ _null_ _null_ ));
+DESCR("emit a binary logical decoding message");
 
 /* event triggers */
 DATA(insert OID = 3566 (  pg_event_trigger_dropped_objects		PGNSP PGUID 12 10 100 0 0 f f f f t t s s 0 0 2249 "" "{26,26,23,16,16,16,25,25,25,25,1009,1009}" "{o,o,o,o,o,o,o,o,o,o,o,o}" "{classid, objid, objsubid, original, normal, is_temporary, object_type, schema_name, object_name, object_identity, address_names, address_args}" _null_ _null_ pg_event_trigger_dropped_objects _null_ _null_ _null_ ));
diff --git a/src/include/replication/logicalfuncs.h b/src/include/replication/logicalfuncs.h
index c87a1df..5540414 100644
--- a/src/include/replication/logicalfuncs.h
+++ b/src/include/replication/logicalfuncs.h
@@ -21,4 +21,6 @@ extern Datum pg_logical_slot_get_binary_changes(PG_FUNCTION_ARGS);
 extern Datum pg_logical_slot_peek_changes(PG_FUNCTION_ARGS);
 extern Datum pg_logical_slot_peek_binary_changes(PG_FUNCTION_ARGS);
 
+extern Datum pg_logical_emit_message_bytea(PG_FUNCTION_ARGS);
+extern Datum pg_logical_emit_message_text(PG_FUNCTION_ARGS);
 #endif
diff --git a/src/include/replication/message.h b/src/include/replication/message.h
new file mode 100644
index 0000000..b1730c9
--- /dev/null
+++ b/src/include/replication/message.h
@@ -0,0 +1,41 @@
+/*-------------------------------------------------------------------------
+ * message.h
+ *	   Exports from replication/logical/message.c
+ *
+ * Copyright (c) 2013-2016, PostgreSQL Global Development Group
+ *
+ * src/include/replication/message.h
+ *-------------------------------------------------------------------------
+ */
+#ifndef PG_LOGICAL_MESSAGE_H
+#define PG_LOGICAL_MESSAGE_H
+
+#include "access/xlog.h"
+#include "access/xlogdefs.h"
+#include "access/xlogreader.h"
+
+/*
+ * Generic logical decoding message wal record.
+ */
+typedef struct xl_logical_message
+{
+	bool		transactional;					/* is message transactional? */
+	size_t		prefix_size;					/* length of prefix */
+	size_t		message_size;					/* size of the message */
+	char		message[FLEXIBLE_ARRAY_MEMBER];	/* message including the null
+												 * terminated prefx of length
+												 * prefix_size */
+} xl_logical_message;
+
+#define SizeOfLogicalMessage	(offsetof(xl_logical_message, message))
+
+extern XLogRecPtr LogLogicalMessage(const char *prefix, const char *message,
+									size_t size, bool transactional);
+
+/* RMGR API*/
+#define XLOG_LOGICAL_MESSAGE	0x00
+void		logicalmsg_redo(XLogReaderState *record);
+void		logicalmsg_desc(StringInfo buf, XLogReaderState *record);
+const char *logicalmsg_identify(uint8 info);
+
+#endif   /* PG_LOGICAL_MESSAGE_H */
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 577b12e..3a2ca98 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -74,6 +74,18 @@ typedef void (*LogicalDecodeCommitCB) (
 												   XLogRecPtr commit_lsn);
 
 /*
+ * Called for the generic logical decoding messages.
+ */
+typedef void (*LogicalDecodeMessageCB) (
+											 struct LogicalDecodingContext *,
+											 ReorderBufferTXN *txn,
+											 XLogRecPtr message_lsn,
+											 bool transactional,
+											 const char *prefix,
+											 Size message_size,
+											 const char *message);
+
+/*
  * Filter changes by origin.
  */
 typedef bool (*LogicalDecodeFilterByOriginCB) (
@@ -96,6 +108,7 @@ typedef struct OutputPluginCallbacks
 	LogicalDecodeBeginCB begin_cb;
 	LogicalDecodeChangeCB change_cb;
 	LogicalDecodeCommitCB commit_cb;
+	LogicalDecodeMessageCB message_cb;
 	LogicalDecodeFilterByOriginCB filter_by_origin_cb;
 	LogicalDecodeShutdownCB shutdown_cb;
 } OutputPluginCallbacks;
diff --git a/src/include/replication/reorderbuffer.h b/src/include/replication/reorderbuffer.h
index b52d06a..c7a970a 100644
--- a/src/include/replication/reorderbuffer.h
+++ b/src/include/replication/reorderbuffer.h
@@ -54,6 +54,7 @@ enum ReorderBufferChangeType
 	REORDER_BUFFER_CHANGE_INSERT,
 	REORDER_BUFFER_CHANGE_UPDATE,
 	REORDER_BUFFER_CHANGE_DELETE,
+	REORDER_BUFFER_CHANGE_MESSAGE,
 	REORDER_BUFFER_CHANGE_INTERNAL_SNAPSHOT,
 	REORDER_BUFFER_CHANGE_INTERNAL_COMMAND_ID,
 	REORDER_BUFFER_CHANGE_INTERNAL_TUPLECID,
@@ -98,6 +99,14 @@ typedef struct ReorderBufferChange
 			ReorderBufferTupleBuf *newtuple;
 		}			tp;
 
+		struct
+		{
+			bool transactional;
+			char *prefix;
+			size_t message_size;
+			char *message;
+		} msg;
+
 		/* New snapshot, set when action == *_INTERNAL_SNAPSHOT */
 		Snapshot	snapshot;
 
@@ -274,6 +283,15 @@ typedef void (*ReorderBufferCommitCB) (
 												   ReorderBufferTXN *txn,
 												   XLogRecPtr commit_lsn);
 
+/* message callback signature */
+typedef void (*ReorderBufferMessageCB) (
+												   ReorderBuffer *rb,
+												   ReorderBufferTXN *txn,
+												   XLogRecPtr message_lsn,
+												   bool transactional,
+												   const char *prefix, Size sz,
+												   const char *message);
+
 struct ReorderBuffer
 {
 	/*
@@ -300,6 +318,7 @@ struct ReorderBuffer
 	ReorderBufferBeginCB begin;
 	ReorderBufferApplyChangeCB apply_change;
 	ReorderBufferCommitCB commit;
+	ReorderBufferMessageCB message;
 
 	/*
 	 * Pointer that will be passed untouched to the callbacks.
@@ -350,6 +369,8 @@ ReorderBufferChange *ReorderBufferGetChange(ReorderBuffer *);
 void		ReorderBufferReturnChange(ReorderBuffer *, ReorderBufferChange *);
 
 void		ReorderBufferQueueChange(ReorderBuffer *, TransactionId, XLogRecPtr lsn, ReorderBufferChange *);
+void		ReorderBufferQueueMessage(ReorderBuffer *, TransactionId, XLogRecPtr lsn,
+									  const char *prefix, Size msg_sz, const char *msg);
 void ReorderBufferCommit(ReorderBuffer *, TransactionId,
 					XLogRecPtr commit_lsn, XLogRecPtr end_lsn,
 	  TimestampTz commit_time, RepOriginId origin_id, XLogRecPtr origin_lsn);
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index 75955af..c4127a1 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -63,6 +63,8 @@ extern const char *SnapBuildExportSnapshot(SnapBuild *snapstate);
 extern void SnapBuildClearExportedSnapshot(void);
 
 extern SnapBuildState SnapBuildCurrentState(SnapBuild *snapstate);
+extern Snapshot SnapBuildGetOrBuildSnapshot(SnapBuild *builder,
+											TransactionId xid);
 
 extern bool SnapBuildXactNeedsSkip(SnapBuild *snapstate, XLogRecPtr ptr);
 
-- 
1.9.1

diff --git a/contrib/pglogical/pglogical.c b/contrib/pglogical/pglogical.c
index f25b91d..6935d0b 100644
--- a/contrib/pglogical/pglogical.c
+++ b/contrib/pglogical/pglogical.c
@@ -25,9 +25,13 @@
 
 #include "mb/pg_wchar.h"
 
+#include "replication/message.h"
+
 #include "storage/ipc.h"
 #include "storage/proc.h"
 
+#include "tcop/utility.h"
+
 #include "utils/builtins.h"
 #include "utils/lsyscache.h"
 
@@ -51,8 +55,10 @@ bool	pglogical_synchronous_commit = false;
 char   *pglogical_temp_directory;
 
 void _PG_init(void);
+void _PG_fini(void);
 void pglogical_supervisor_main(Datum main_arg);
 
+static ProcessUtility_hook_type prev_utility_hook = NULL;
 
 /*
  * Ensure string is not longer than maxlen.
@@ -400,6 +406,38 @@ pglogical_supervisor_main(Datum main_arg)
 	proc_exit(1);
 }
 
+static void
+emit_message_utility(Node *parsetree,
+					 const char *queryString,
+					 ProcessUtilityContext context,
+					 ParamListInfo params,
+					 DestReceiver *dest,
+					 char *completionTag)
+{
+	NodeTag		stmtType = nodeTag(parsetree);
+
+	if (context == PROCESS_UTILITY_TOPLEVEL &&
+		/*
+		 * Create and drop statements are handled. Can be added more tags from
+		 * nodes.h.
+		 */
+		(stmtType == T_CreateStmt || stmtType == T_DropStmt))
+		LogLogicalMessage("pglogical",
+						  queryString, strlen(queryString), true);
+
+	/*
+	 * Fallback to normal process, be it the previous hook loaded
+	 * or the in-core code path if the previous hook does not exist.
+	 */
+	if (prev_utility_hook)
+		(*prev_utility_hook) (parsetree, queryString,
+							  context, params,
+							  dest, completionTag);
+	else
+		standard_ProcessUtility(parsetree, queryString,
+								context, params,
+								dest, completionTag);
+}
 
 /*
  * Entry point for this module.
@@ -442,6 +480,10 @@ _PG_init(void)
 							   "/tmp", PGC_SIGHUP,
 							   0,
 							   NULL, NULL, NULL);
+
+	prev_utility_hook = ProcessUtility_hook;
+	ProcessUtility_hook = emit_message_utility;
+
 	if (IsBinaryUpgrade)
 		return;
 
@@ -465,3 +507,9 @@ _PG_init(void)
 
 	RegisterBackgroundWorker(&bgw);
 }
+
+void
+_PG_fini(void)
+{
+	ProcessUtility_hook = prev_utility_hook;
+}
\ No newline at end of file
diff --git a/contrib/pglogical/pglogical_apply.c b/contrib/pglogical/pglogical_apply.c
index bf5615c..8f78fef 100644
--- a/contrib/pglogical/pglogical_apply.c
+++ b/contrib/pglogical/pglogical_apply.c
@@ -684,6 +684,19 @@ handle_delete(StringInfo s)
 	CommandCounterIncrement();
 }
 
+static void
+handle_ddl(StringInfo s)
+{
+	char		   *query = pglogical_read_ddl(s);
+	bool			started_tx = ensure_transaction();
+
+	/* Execute the query locally. */
+	pglogical_execute_sql_command(query, GetUserNameFromId(GetUserId(), false),
+								  started_tx);
+
+	CommandCounterIncrement();
+}
+
 inline static bool
 getmsgisend(StringInfo msg)
 {
@@ -1045,6 +1058,10 @@ replication_handler(StringInfo s)
 		case 'S':
 			handle_startup(s);
 			break;
+		/* DDL MESSAGE */
+		case 'M':
+			handle_ddl(s);
+			break;
 		default:
 			elog(ERROR, "unknown action of type %c", action);
 	}
diff --git a/contrib/pglogical/pglogical_proto.c b/contrib/pglogical/pglogical_proto.c
index 558a955..133c1c0 100644
--- a/contrib/pglogical/pglogical_proto.c
+++ b/contrib/pglogical/pglogical_proto.c
@@ -230,6 +230,27 @@ pglogical_read_delete(StringInfo in, LOCKMODE lockmode,
 	return rel;
 }
 
+/*
+ * Read DDL command from stream.
+ *
+ * Returns DDL query.
+ */
+char *
+pglogical_read_ddl(StringInfo in)
+{
+	uint8		flags;
+	Size		sz;
+
+	/* read the flags */
+	flags = pq_getmsgbyte(in);
+	Assert(flags == 0);
+
+	/* read the message lengh */
+	sz = pq_getmsgint(in, 4);
+
+	/* read the message */
+	return (char *) pq_getmsgbytes(in, sz);
+}
 
 /*
  * Read tuple in remote format from stream.
@@ -407,7 +428,7 @@ pglogical_read_attrs(StringInfo in, char ***attrnames, int *nattrnames)
 		if (blocktype != 'C')
 			elog(ERROR, "expected COLUMN, got %c", blocktype);
 		flags = pq_getmsgbyte(in);
-//		Assert(flags == 0);
+		Assert(flags >= 0);
 
 		blocktype = pq_getmsgbyte(in);		/* column name block follows */
 		if (blocktype != 'N')
diff --git a/contrib/pglogical/pglogical_proto.h b/contrib/pglogical/pglogical_proto.h
index 3229c322..1d2e055 100644
--- a/contrib/pglogical/pglogical_proto.h
+++ b/contrib/pglogical/pglogical_proto.h
@@ -38,5 +38,6 @@ extern PGLogicalRelation *pglogical_read_update(StringInfo in, LOCKMODE lockmode
 					   PGLogicalTupleData *oldtup, PGLogicalTupleData *newtup);
 extern PGLogicalRelation *pglogical_read_delete(StringInfo in, LOCKMODE lockmode,
 												 PGLogicalTupleData *oldtup);
+extern char *pglogical_read_ddl(StringInfo in);
 
 #endif /* PGLOGICAL_PROTO_H */
diff --git a/contrib/pglogical/pglogical_worker.c b/contrib/pglogical/pglogical_worker.c
index cc37866..1a3ca21 100644
--- a/contrib/pglogical/pglogical_worker.c
+++ b/contrib/pglogical/pglogical_worker.c
@@ -406,7 +406,11 @@ pglogical_worker_shmem_startup(void)
 
 	if (!found)
 	{
-		PGLogicalCtx->lock = LWLockAssign();
+		#if PG_VERSION_NUM >= 90600
+		PGLogicalCtx->lock = &(GetNamedLWLockTranche(EXTENSION_NAME))->lock;
+		#else
+		PGLogicalCtx->lock  = LWLockAssign();
+		#endif
 		PGLogicalCtx->supervisor = NULL;
 		PGLogicalCtx->total_workers = max_worker_processes;
 		memset(PGLogicalCtx->workers, 0,
@@ -430,7 +434,11 @@ pglogical_worker_shmem_init(void)
 	 * tries to allocate or free blocks from this array at once.  There won't
 	 * be enough contention to make anything fancier worth doing.
 	 */
+	#if PG_VERSION_NUM >= 90600
+	RequestNamedLWLockTranche(EXTENSION_NAME, 1);
+	#else
 	RequestAddinLWLocks(1);
+	#endif
 
 	/*
 	 * Whether this is a first startup or crash recovery, we'll be re-initing
diff --git a/contrib/pglogical_output/pglogical_output.c b/contrib/pglogical_output/pglogical_output.c
index 5262d82..3181c6c 100644
--- a/contrib/pglogical_output/pglogical_output.c
+++ b/contrib/pglogical_output/pglogical_output.c
@@ -66,6 +66,10 @@ static void pg_decode_commit_txn(LogicalDecodingContext *ctx,
 static void pg_decode_change(LogicalDecodingContext *ctx,
 				 ReorderBufferTXN *txn, Relation rel,
 				 ReorderBufferChange *change);
+static void pg_decode_message(LogicalDecodingContext *ctx,
+							  ReorderBufferTXN *txn, XLogRecPtr message_lsn,
+							  bool transactional, const char *prefix,
+							  Size sz, const char *message);
 
 #ifdef HAVE_REPLICATION_ORIGINS
 static bool pg_decode_origin_filter(LogicalDecodingContext *ctx,
@@ -87,6 +91,7 @@ _PG_output_plugin_init(OutputPluginCallbacks *cb)
 	cb->begin_cb = pg_decode_begin_txn;
 	cb->change_cb = pg_decode_change;
 	cb->commit_cb = pg_decode_commit_txn;
+	cb->message_cb = pg_decode_message;
 #ifdef HAVE_REPLICATION_ORIGINS
 	cb->filter_by_origin_cb = pg_decode_origin_filter;
 #endif
@@ -254,7 +259,7 @@ pg_decode_startup(LogicalDecodingContext * ctx, OutputPluginOptions *opt,
 			ereport(ERROR,
 				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
 				 errmsg("client requested protocol %s but only \"json\" or \"native\" are supported",
-				 	data->client_protocol_format)));
+					data->client_protocol_format)));
 		}
 
 		/* check for encoding match if specific encoding demanded by client */
@@ -512,6 +517,22 @@ pg_decode_change(LogicalDecodingContext *ctx, ReorderBufferTXN *txn,
 	MemoryContextReset(data->context);
 }
 
+static void
+pg_decode_message(LogicalDecodingContext *ctx,
+				  ReorderBufferTXN *txn, XLogRecPtr message_lsn,
+				  bool transactional, const char *prefix,
+				  Size sz, const char *message)
+{
+	PGLogicalOutputData *data = ctx->output_plugin_private;
+
+	if (strcmp(prefix, "pglogical") == 0)
+	{
+		OutputPluginPrepareWrite(ctx, true);
+		data->api->write_ddl(ctx->out, data, message, sz);
+		OutputPluginWrite(ctx, true);
+	}
+}
+
 #ifdef HAVE_REPLICATION_ORIGINS
 /*
  * Decide if the whole transaction with specific origin should be filtered out.
diff --git a/contrib/pglogical_output/pglogical_proto.c b/contrib/pglogical_output/pglogical_proto.c
index 47a883f..a1e6b85 100644
--- a/contrib/pglogical_output/pglogical_proto.c
+++ b/contrib/pglogical_output/pglogical_proto.c
@@ -31,6 +31,7 @@ pglogical_init_api(PGLogicalProtoType typ)
 		res->write_insert = pglogical_json_write_insert;
 		res->write_update = pglogical_json_write_update;
 		res->write_delete = pglogical_json_write_delete;
+		res->write_ddl = pglogical_json_write_ddl;
 		res->write_startup_message = json_write_startup_message;
 	}
 	else
@@ -42,6 +43,7 @@ pglogical_init_api(PGLogicalProtoType typ)
 		res->write_insert = pglogical_write_insert;
 		res->write_update = pglogical_write_update;
 		res->write_delete = pglogical_write_delete;
+		res->write_ddl = pglogical_write_ddl;
 		res->write_startup_message = write_startup_message;
 	}
 
diff --git a/contrib/pglogical_output/pglogical_proto.h b/contrib/pglogical_output/pglogical_proto.h
index 27897e2..032803b 100644
--- a/contrib/pglogical_output/pglogical_proto.h
+++ b/contrib/pglogical_output/pglogical_proto.h
@@ -34,6 +34,8 @@ typedef void (*pglogical_write_update_fn)(StringInfo out, struct PGLogicalOutput
 							 HeapTuple newtuple);
 typedef void (*pglogical_write_delete_fn)(StringInfo out, struct PGLogicalOutputData *data,
 							 Relation rel, HeapTuple oldtuple);
+typedef void (*pglogical_write_ddl_fn)(StringInfo out, struct PGLogicalOutputData *data,
+							 const char *message, Size sz);
 
 typedef void (*write_startup_message_fn)(StringInfo out, List *msg);
 
@@ -46,6 +48,7 @@ typedef struct PGLogicalProtoAPI
 	pglogical_write_insert_fn	write_insert;
 	pglogical_write_update_fn	write_update;
 	pglogical_write_delete_fn	write_delete;
+	pglogical_write_ddl_fn		write_ddl;
 	write_startup_message_fn	write_startup_message;
 } PGLogicalProtoAPI;
 
diff --git a/contrib/pglogical_output/pglogical_proto_json.c b/contrib/pglogical_output/pglogical_proto_json.c
index ae5a591..70e23c5 100644
--- a/contrib/pglogical_output/pglogical_proto_json.c
+++ b/contrib/pglogical_output/pglogical_proto_json.c
@@ -178,6 +178,18 @@ pglogical_json_write_delete(StringInfo out, PGLogicalOutputData *data,
 }
 
 /*
+ * Write DDL logical message to the output stream.
+ */
+void
+pglogical_json_write_ddl(StringInfo out, PGLogicalOutputData *data,
+							const char *message, Size sz)
+{
+	appendStringInfoString(out, "{\"action\":\"M\", \"message\":");
+	appendBinaryStringInfo(out, message, sz);
+	appendStringInfoString(out, "}");
+}
+
+/*
  * The startup message should be constructed as a json object, one
  * key/value per DefElem list member.
  */
diff --git a/contrib/pglogical_output/pglogical_proto_json.h b/contrib/pglogical_output/pglogical_proto_json.h
index d853e9e..03ccfc0 100644
--- a/contrib/pglogical_output/pglogical_proto_json.h
+++ b/contrib/pglogical_output/pglogical_proto_json.h
@@ -26,6 +26,8 @@ extern void pglogical_json_write_update(StringInfo out, PGLogicalOutputData *dat
 								 HeapTuple newtuple);
 extern void pglogical_json_write_delete(StringInfo out, PGLogicalOutputData *data,
 								 Relation rel, HeapTuple oldtuple);
+extern void pglogical_json_write_ddl(StringInfo out, PGLogicalOutputData *data,
+								 const char *message, Size sz);
 
 extern void json_write_startup_message(StringInfo out, List *msg);
 
diff --git a/contrib/pglogical_output/pglogical_proto_native.c b/contrib/pglogical_output/pglogical_proto_native.c
index 87ec453..f6630a2 100644
--- a/contrib/pglogical_output/pglogical_proto_native.c
+++ b/contrib/pglogical_output/pglogical_proto_native.c
@@ -318,6 +318,24 @@ pglogical_write_delete(StringInfo out, PGLogicalOutputData *data,
 }
 
 /*
+ * Write DDL logical message to the output stream.
+ */
+void
+pglogical_write_ddl(StringInfo out, PGLogicalOutputData *data,
+					const char *message, Size sz)
+{
+	uint8 flags = 0;
+
+	pq_sendbyte(out, 'M');		/* action DDL message */
+
+	/* send the flags field */
+	pq_sendbyte(out, flags);
+
+	pq_sendint(out, sz, 4);		/* message length */
+	pq_sendbytes(out, message, sz);
+}
+
+/*
  * Most of the brains for startup message creation lives in
  * pglogical_config.c, so this presently just sends the set of key/value pairs.
  */
diff --git a/contrib/pglogical_output/pglogical_proto_native.h b/contrib/pglogical_output/pglogical_proto_native.h
index d3ba125..c02d63e 100644
--- a/contrib/pglogical_output/pglogical_proto_native.h
+++ b/contrib/pglogical_output/pglogical_proto_native.h
@@ -41,6 +41,8 @@ extern void pglogical_write_update(StringInfo out, PGLogicalOutputData *data,
 							HeapTuple newtuple);
 extern void pglogical_write_delete(StringInfo out, PGLogicalOutputData *data,
 							Relation rel, HeapTuple oldtuple);
+extern void pglogical_write_ddl(StringInfo out, PGLogicalOutputData *data,
+							const char *message, Size sz);
 
 extern void write_startup_message(StringInfo out, List *msg);
 

From 4515b5b3e8f5ddb96124e859b968c43c27f79be3 Mon Sep 17 00:00:00 2001
From: Petr Jelinek <pjmodos@pjmodos.net>
Date: Wed, 24 Feb 2016 17:02:36 +0100
Subject: [PATCH] Logical Decoding Messages

---
 contrib/test_decoding/Makefile                  |  2 +-
 contrib/test_decoding/expected/ddl.out          | 21 ++++--
 contrib/test_decoding/expected/messages.out     | 56 ++++++++++++++++
 contrib/test_decoding/sql/ddl.sql               |  3 +-
 contrib/test_decoding/sql/messages.sql          | 17 +++++
 contrib/test_decoding/test_decoding.c           | 17 +++++
 doc/src/sgml/func.sgml                          | 45 +++++++++++++
 doc/src/sgml/logicaldecoding.sgml               | 34 ++++++++++
 src/backend/access/rmgrdesc/Makefile            |  4 +-
 src/backend/access/rmgrdesc/logicalmsgdesc.c    | 41 ++++++++++++
 src/backend/access/transam/rmgr.c               |  1 +
 src/backend/replication/logical/Makefile        |  2 +-
 src/backend/replication/logical/decode.c        | 49 ++++++++++++++
 src/backend/replication/logical/logical.c       | 37 +++++++++++
 src/backend/replication/logical/logicalfuncs.c  | 27 ++++++++
 src/backend/replication/logical/message.c       | 87 +++++++++++++++++++++++++
 src/backend/replication/logical/reorderbuffer.c | 68 +++++++++++++++++++
 src/backend/replication/logical/snapbuild.c     | 19 ++++++
 src/bin/pg_xlogdump/rmgrdesc.c                  |  1 +
 src/include/access/rmgrlist.h                   |  1 +
 src/include/catalog/pg_proc.h                   |  4 ++
 src/include/replication/logicalfuncs.h          |  2 +
 src/include/replication/message.h               | 41 ++++++++++++
 src/include/replication/output_plugin.h         | 12 ++++
 src/include/replication/reorderbuffer.h         | 20 ++++++
 src/include/replication/snapbuild.h             |  2 +
 26 files changed, 601 insertions(+), 12 deletions(-)
 create mode 100644 contrib/test_decoding/expected/messages.out
 create mode 100644 contrib/test_decoding/sql/messages.sql
 create mode 100644 src/backend/access/rmgrdesc/logicalmsgdesc.c
 create mode 100644 src/backend/replication/logical/message.c
 create mode 100644 src/include/replication/message.h

diff --git a/contrib/test_decoding/Makefile b/contrib/test_decoding/Makefile
index 06c9546..309cb0b 100644
--- a/contrib/test_decoding/Makefile
+++ b/contrib/test_decoding/Makefile
@@ -38,7 +38,7 @@ submake-test_decoding:
 	$(MAKE) -C $(top_builddir)/contrib/test_decoding
 
 REGRESSCHECKS=ddl xact rewrite toast permissions decoding_in_xact \
-	decoding_into_rel binary prepared replorigin time
+	decoding_into_rel binary prepared replorigin time messages
 
 regresscheck: | submake-regress submake-test_decoding temp-install
 	$(MKDIR_P) regression_output
diff --git a/contrib/test_decoding/expected/ddl.out b/contrib/test_decoding/expected/ddl.out
index 77719e8..32cd24d 100644
--- a/contrib/test_decoding/expected/ddl.out
+++ b/contrib/test_decoding/expected/ddl.out
@@ -220,11 +220,17 @@ SELECT data FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'inc
 (7 rows)
 
 /*
- * check that disk spooling works
+ * check that disk spooling works (also for logical messages)
  */
 BEGIN;
 CREATE TABLE tr_etoomuch (id serial primary key, data int);
 INSERT INTO tr_etoomuch(data) SELECT g.i FROM generate_series(1, 10234) g(i);
+SELECT 'tx logical msg' FROM pg_logical_emit_message(true, 'test', 'tx logical msg');
+    ?column?    
+----------------
+ tx logical msg
+(1 row)
+
 DELETE FROM tr_etoomuch WHERE id < 5000;
 UPDATE tr_etoomuch SET data = - data WHERE id > 5000;
 COMMIT;
@@ -233,12 +239,13 @@ SELECT count(*), min(data), max(data)
 FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'include-xids', '0', 'skip-empty-xacts', '1')
 GROUP BY substring(data, 1, 24)
 ORDER BY 1,2;
- count |                       min                       |                                  max                                   
--------+-------------------------------------------------+------------------------------------------------------------------------
-     1 | BEGIN                                           | BEGIN
-     1 | COMMIT                                          | COMMIT
- 20467 | table public.tr_etoomuch: DELETE: id[integer]:1 | table public.tr_etoomuch: UPDATE: id[integer]:9999 data[integer]:-9999
-(3 rows)
+ count |                                  min                                  |                                  max                                   
+-------+-----------------------------------------------------------------------+------------------------------------------------------------------------
+     1 | BEGIN                                                                 | BEGIN
+     1 | COMMIT                                                                | COMMIT
+     1 | message: transactional: 1 prefix: test, sz: 14 content:tx logical msg | message: transactional: 1 prefix: test, sz: 14 content:tx logical msg
+ 20467 | table public.tr_etoomuch: DELETE: id[integer]:1                       | table public.tr_etoomuch: UPDATE: id[integer]:9999 data[integer]:-9999
+(4 rows)
 
 -- check updates of primary keys work correctly
 BEGIN;
diff --git a/contrib/test_decoding/expected/messages.out b/contrib/test_decoding/expected/messages.out
new file mode 100644
index 0000000..7fa8256
--- /dev/null
+++ b/contrib/test_decoding/expected/messages.out
@@ -0,0 +1,56 @@
+-- predictability
+SET synchronous_commit = on;
+SELECT 'init' FROM pg_create_logical_replication_slot('regression_slot', 'test_decoding');
+ ?column? 
+----------
+ init
+(1 row)
+
+SELECT 'msg1' FROM pg_logical_emit_message(true, 'test', 'msg1');
+ ?column? 
+----------
+ msg1
+(1 row)
+
+SELECT 'msg2' FROM pg_logical_emit_message(false, 'test', 'msg2');
+ ?column? 
+----------
+ msg2
+(1 row)
+
+BEGIN;
+SELECT 'msg3' FROM pg_logical_emit_message(true, 'test', 'msg3');
+ ?column? 
+----------
+ msg3
+(1 row)
+
+SELECT 'msg4' FROM pg_logical_emit_message(false, 'test', 'msg4');
+ ?column? 
+----------
+ msg4
+(1 row)
+
+SELECT 'msg5' FROM pg_logical_emit_message(true, 'test', 'msg5');
+ ?column? 
+----------
+ msg5
+(1 row)
+
+COMMIT;
+SELECT data FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'force-binary', '0', 'skip-empty-xacts', '1');
+                            data                            
+------------------------------------------------------------
+ message: transactional: 1 prefix: test, sz: 4 content:msg1
+ message: transactional: 0 prefix: test, sz: 4 content:msg2
+ message: transactional: 0 prefix: test, sz: 4 content:msg4
+ message: transactional: 1 prefix: test, sz: 4 content:msg3
+ message: transactional: 1 prefix: test, sz: 4 content:msg5
+(5 rows)
+
+SELECT 'init' FROM pg_drop_replication_slot('regression_slot');
+ ?column? 
+----------
+ init
+(1 row)
+
diff --git a/contrib/test_decoding/sql/ddl.sql b/contrib/test_decoding/sql/ddl.sql
index ad928ad..b1f7bf6 100644
--- a/contrib/test_decoding/sql/ddl.sql
+++ b/contrib/test_decoding/sql/ddl.sql
@@ -108,11 +108,12 @@ DELETE FROM tr_pkey;
 SELECT data FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'include-xids', '0', 'skip-empty-xacts', '1');
 
 /*
- * check that disk spooling works
+ * check that disk spooling works (also for logical messages)
  */
 BEGIN;
 CREATE TABLE tr_etoomuch (id serial primary key, data int);
 INSERT INTO tr_etoomuch(data) SELECT g.i FROM generate_series(1, 10234) g(i);
+SELECT 'tx logical msg' FROM pg_logical_emit_message(true, 'test', 'tx logical msg');
 DELETE FROM tr_etoomuch WHERE id < 5000;
 UPDATE tr_etoomuch SET data = - data WHERE id > 5000;
 COMMIT;
diff --git a/contrib/test_decoding/sql/messages.sql b/contrib/test_decoding/sql/messages.sql
new file mode 100644
index 0000000..8744eb6
--- /dev/null
+++ b/contrib/test_decoding/sql/messages.sql
@@ -0,0 +1,17 @@
+-- predictability
+SET synchronous_commit = on;
+
+SELECT 'init' FROM pg_create_logical_replication_slot('regression_slot', 'test_decoding');
+
+SELECT 'msg1' FROM pg_logical_emit_message(true, 'test', 'msg1');
+SELECT 'msg2' FROM pg_logical_emit_message(false, 'test', 'msg2');
+
+BEGIN;
+SELECT 'msg3' FROM pg_logical_emit_message(true, 'test', 'msg3');
+SELECT 'msg4' FROM pg_logical_emit_message(false, 'test', 'msg4');
+SELECT 'msg5' FROM pg_logical_emit_message(true, 'test', 'msg5');
+COMMIT;
+
+SELECT data FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'force-binary', '0', 'skip-empty-xacts', '1');
+
+SELECT 'init' FROM pg_drop_replication_slot('regression_slot');
diff --git a/contrib/test_decoding/test_decoding.c b/contrib/test_decoding/test_decoding.c
index 4cf808f..1997774 100644
--- a/contrib/test_decoding/test_decoding.c
+++ b/contrib/test_decoding/test_decoding.c
@@ -21,6 +21,7 @@
 
 #include "replication/output_plugin.h"
 #include "replication/logical.h"
+#include "replication/message.h"
 #include "replication/origin.h"
 
 #include "utils/builtins.h"
@@ -63,6 +64,9 @@ static void pg_decode_change(LogicalDecodingContext *ctx,
 				 ReorderBufferChange *change);
 static bool pg_decode_filter(LogicalDecodingContext *ctx,
 				 RepOriginId origin_id);
+static void pg_decode_message(LogicalDecodingContext *ctx,
+							  ReorderBufferTXN *txn, XLogRecPtr message_lsn,
+							  const char *prefix, Size sz, const char *message);
 
 void
 _PG_init(void)
@@ -82,6 +86,7 @@ _PG_output_plugin_init(OutputPluginCallbacks *cb)
 	cb->commit_cb = pg_decode_commit_txn;
 	cb->filter_by_origin_cb = pg_decode_filter;
 	cb->shutdown_cb = pg_decode_shutdown;
+	cb->message_cb = pg_decode_message;
 }
 
 
@@ -471,3 +476,15 @@ pg_decode_change(LogicalDecodingContext *ctx, ReorderBufferTXN *txn,
 
 	OutputPluginWrite(ctx, true);
 }
+
+static void
+pg_decode_message(LogicalDecodingContext *ctx,
+				  ReorderBufferTXN *txn, XLogRecPtr lsn,
+				  const char *prefix, Size sz, const char *message)
+{
+	OutputPluginPrepareWrite(ctx, true);
+	appendStringInfo(ctx->out, "message: transactional: %d prefix: %s, sz: %zu content:",
+					 txn != NULL, prefix, sz);
+	appendBinaryStringInfo(ctx->out, message, sz);
+	OutputPluginWrite(ctx, true);
+}
diff --git a/doc/src/sgml/func.sgml b/doc/src/sgml/func.sgml
index ae93e69..02f556b 100644
--- a/doc/src/sgml/func.sgml
+++ b/doc/src/sgml/func.sgml
@@ -18238,6 +18238,51 @@ postgres=# SELECT * FROM pg_xlogfile_name_offset(pg_stop_backup());
        </entry>
       </row>
 
+      <row>
+       <entry id="pg-logical-emit-message-text">
+        <indexterm>
+         <primary>pg_logical_emit_message</primary>
+        </indexterm>
+        <literal><function>pg_logical_emit_message(<parameter>transactional</parameter> <type>bool</type>, <parameter>prefix</parameter> <type>text</type>, <parameter>content</parameter> <type>text</type>)</function></literal>
+       </entry>
+       <entry>
+        void
+       </entry>
+       <entry>
+        Write text logical decoding message. This can be used to pass generic
+        messages to logical decoding plugins through WAL. The parameter
+        <parameter>transactional</parameter> specifies if the message should
+        be part of current transaction or if it should be written immediately
+        and decoded as soon as the logical decoding reads the record. The
+        <parameter>prefix</parameter> is textual prefix used by the logical
+        decoding plugins to easily recognize interesting messages for them.
+        The <parameter>content</parameter> is the text of the message.
+       </entry>
+      </row>
+
+      <row>
+       <entry id="pg-logical-emit-message-bytea">
+        <indexterm>
+         <primary>>pg_logical_emit_message</primary>
+        </indexterm>
+        <literal><function>>pg_logical_emit_message(<parameter>transactional</parameter> <type>bool</type>, <parameter>prefix</parameter> <type>text</type>, <parameter>content</parameter> <type>bytea</type>)</function></literal>
+       </entry>
+       <entry>
+        void
+       </entry>
+       <entry>
+        Write binary logical decoding message. This can be used to pass generic
+        messages to logical decoding plugins through WAL. The parameter
+        <parameter>transactional</parameter> specifies if the message should
+        be part of current transaction or if it should be written immediately
+        and decoded as soon as the logical decoding reads the record. The
+        <parameter>prefix</parameter> is textual prefix used by the logical
+        decoding plugins to easily recognize interesting messages for them.
+        The <parameter>content</parameter> is the binary content of the
+        message.
+       </entry>
+      </row>
+
      </tbody>
     </tgroup>
    </table>
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 45fdfeb..7c9d03a 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -363,6 +363,7 @@ typedef struct OutputPluginCallbacks
     LogicalDecodeBeginCB begin_cb;
     LogicalDecodeChangeCB change_cb;
     LogicalDecodeCommitCB commit_cb;
+    LogicalDecodeMessageCB message_cb;
     LogicalDecodeFilterByOriginCB filter_by_origin_cb;
     LogicalDecodeShutdownCB shutdown_cb;
 } OutputPluginCallbacks;
@@ -602,6 +603,39 @@ typedef bool (*LogicalDecodeFilterByOriginCB) (
        more efficient.
      </para>
      </sect3>
+
+    <sect3 id="logicaldecoding-output-plugin-message">
+     <title>Generic Message Callback</title>
+
+     <para>
+      The optional <function>message_cb</function> callback is called whenever
+      a logical decoding message has been decoded.
+<programlisting>
+typedef void (*LogicalDecodeMessageCB) (
+    struct LogicalDecodingContext *,
+    ReorderBufferTXN *txn,
+    XLogRecPtr message_lsn,
+    const char *prefix,
+    Size message_size,
+    const char *message
+);
+</programlisting>
+      The <parameter>ctx</parameter> and <parameter>txn</parameter> parameters
+      have the same contents as for the <function>begin_cb</function> with the
+      difference that <parameter>txn</parameter> is null for non-transactional
+      messages. The <parameter>lsn</parameter> has WAL position of the message.
+      The <parameter>prefix</parameter> is arbitrary textual prefix which can
+      be used for identifying interesting messages for the current plugin.
+      And finally the <parameter>message</parameter> parameter holds the
+      actual message of <parameter>message_size</parameter> size.
+     </para>
+     <para>
+      Extra care should be taken to ensure that the prefix the output plugin
+      considers interesting is unique. Using name of the extension or the
+      output plugin itself is often a good choice.
+     </para>
+    </sect3>
+
    </sect2>
 
    <sect2 id="logicaldecoding-output-plugin-output">
diff --git a/src/backend/access/rmgrdesc/Makefile b/src/backend/access/rmgrdesc/Makefile
index c72a1f2..723b4d8 100644
--- a/src/backend/access/rmgrdesc/Makefile
+++ b/src/backend/access/rmgrdesc/Makefile
@@ -9,8 +9,8 @@ top_builddir = ../../../..
 include $(top_builddir)/src/Makefile.global
 
 OBJS = brindesc.o clogdesc.o committsdesc.o dbasedesc.o gindesc.o gistdesc.o \
-	   hashdesc.o heapdesc.o mxactdesc.o nbtdesc.o relmapdesc.o \
-	   replorigindesc.o seqdesc.o smgrdesc.o spgdesc.o \
+	   hashdesc.o heapdesc.o logicalmsgdesc.o mxactdesc.o nbtdesc.o \
+	   relmapdesc.o replorigindesc.o seqdesc.o smgrdesc.o spgdesc.o \
 	   standbydesc.o tblspcdesc.o xactdesc.o xlogdesc.o
 
 include $(top_srcdir)/src/backend/common.mk
diff --git a/src/backend/access/rmgrdesc/logicalmsgdesc.c b/src/backend/access/rmgrdesc/logicalmsgdesc.c
new file mode 100644
index 0000000..b194e14
--- /dev/null
+++ b/src/backend/access/rmgrdesc/logicalmsgdesc.c
@@ -0,0 +1,41 @@
+/*-------------------------------------------------------------------------
+ *
+ * logicalmsgdesc.c
+ *	  rmgr descriptor routines for replication/logical/message.c
+ *
+ * Portions Copyright (c) 2015-2016, PostgreSQL Global Development Group
+ *
+ *
+ * IDENTIFICATION
+ *	  src/backend/access/rmgrdesc/logicalmsgdesc.c
+ *
+ *-------------------------------------------------------------------------
+ */
+#include "postgres.h"
+
+#include "replication/message.h"
+
+void
+logicalmsg_desc(StringInfo buf, XLogReaderState *record)
+{
+	char	   *rec = XLogRecGetData(record);
+	uint8		info = XLogRecGetInfo(record) & ~XLR_INFO_MASK;
+
+	if (info == XLOG_LOGICAL_MESSAGE)
+	{
+		xl_logical_message *xlrec = (xl_logical_message *) rec;
+
+		appendStringInfo(buf, "%s message size %zu bytes",
+				   xlrec->transactional ? "transactional" : "nontransactional",
+						 xlrec->message_size);
+	}
+}
+
+const char *
+logicalmsg_identify(uint8 info)
+{
+	if ((info & ~XLR_INFO_MASK) == XLOG_LOGICAL_MESSAGE)
+		return "MESSAGE";
+
+	return NULL;
+}
diff --git a/src/backend/access/transam/rmgr.c b/src/backend/access/transam/rmgr.c
index 7c4d773..1a42121 100644
--- a/src/backend/access/transam/rmgr.c
+++ b/src/backend/access/transam/rmgr.c
@@ -23,6 +23,7 @@
 #include "commands/dbcommands_xlog.h"
 #include "commands/sequence.h"
 #include "commands/tablespace.h"
+#include "replication/message.h"
 #include "replication/origin.h"
 #include "storage/standby.h"
 #include "utils/relmapper.h"
diff --git a/src/backend/replication/logical/Makefile b/src/backend/replication/logical/Makefile
index 8adea13..1d7ca06 100644
--- a/src/backend/replication/logical/Makefile
+++ b/src/backend/replication/logical/Makefile
@@ -14,7 +14,7 @@ include $(top_builddir)/src/Makefile.global
 
 override CPPFLAGS := -I$(srcdir) $(CPPFLAGS)
 
-OBJS = decode.o logical.o logicalfuncs.o reorderbuffer.o origin.o \
+OBJS = decode.o logical.o logicalfuncs.o message.o origin.o reorderbuffer.o \
 	snapbuild.o
 
 include $(top_srcdir)/src/backend/common.mk
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index 13af485..98ec5d9 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -39,6 +39,7 @@
 
 #include "replication/decode.h"
 #include "replication/logical.h"
+#include "replication/message.h"
 #include "replication/reorderbuffer.h"
 #include "replication/origin.h"
 #include "replication/snapbuild.h"
@@ -58,6 +59,7 @@ static void DecodeHeapOp(LogicalDecodingContext *ctx, XLogRecordBuffer *buf);
 static void DecodeHeap2Op(LogicalDecodingContext *ctx, XLogRecordBuffer *buf);
 static void DecodeXactOp(LogicalDecodingContext *ctx, XLogRecordBuffer *buf);
 static void DecodeStandbyOp(LogicalDecodingContext *ctx, XLogRecordBuffer *buf);
+static void DecodeLogicalMsgOp(LogicalDecodingContext *ctx, XLogRecordBuffer *buf);
 
 /* individual record(group)'s handlers */
 static void DecodeInsert(LogicalDecodingContext *ctx, XLogRecordBuffer *buf);
@@ -123,6 +125,10 @@ LogicalDecodingProcessRecord(LogicalDecodingContext *ctx, XLogReaderState *recor
 			DecodeHeapOp(ctx, &buf);
 			break;
 
+		case RM_LOGICALMSG_ID:
+			DecodeLogicalMsgOp(ctx, &buf);
+			break;
+
 			/*
 			 * Rmgrs irrelevant for logical decoding; they describe stuff not
 			 * represented in logical decoding. Add new rmgrs in rmgrlist.h's
@@ -457,6 +463,49 @@ DecodeHeapOp(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
 	}
 }
 
+/*
+ * Handle rmgr LOGICALMSG_ID records for DecodeRecordIntoReorderBuffer().
+ */
+static void
+DecodeLogicalMsgOp(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
+{
+	SnapBuild  *builder = ctx->snapshot_builder;
+	XLogReaderState *r = buf->record;
+	uint8		info = XLogRecGetInfo(r) & ~XLR_INFO_MASK;
+	xl_logical_message *message;
+
+	if (info != XLOG_LOGICAL_MESSAGE)
+		elog(ERROR, "unexpected RM_LOGICALMSG_ID record type: %u", info);
+
+	message = (xl_logical_message *) XLogRecGetData(r);
+
+	if (message->transactional)
+	{
+		if (!SnapBuildProcessChange(builder, XLogRecGetXid(r), buf->origptr))
+			return;
+
+		ReorderBufferQueueMessage(ctx->reorder, XLogRecGetXid(r),
+								  buf->endptr,
+								  message->message, /* first part of message is prefix */
+								  message->message_size,
+								  message->message + message->prefix_size);
+	}
+	else if (SnapBuildCurrentState(builder) == SNAPBUILD_CONSISTENT &&
+			 !SnapBuildXactNeedsSkip(builder, buf->origptr))
+	{
+		volatile Snapshot	snapshot_now;
+		ReorderBuffer	   *rb = ctx->reorder;
+
+		/* setup snapshot to allow catalog access */
+		snapshot_now = SnapBuildGetOrBuildSnapshot(builder, XLogRecGetXid(r));
+		SetupHistoricSnapshot(snapshot_now, NULL);
+		rb->message(rb, NULL, buf->origptr, message->message,
+					message->message_size,
+					message->message + message->prefix_size);
+		TeardownHistoricSnapshot(false);
+	}
+}
+
 static inline bool
 FilterByOrigin(LogicalDecodingContext *ctx, RepOriginId origin_id)
 {
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index 2e6d3f9..7863d52 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -62,6 +62,9 @@ static void commit_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
 				  XLogRecPtr commit_lsn);
 static void change_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
 				  Relation relation, ReorderBufferChange *change);
+static void message_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
+				  XLogRecPtr message_lsn, const char *prefix, Size sz,
+				  const char *message);
 
 static void LoadOutputPlugin(OutputPluginCallbacks *callbacks, char *plugin);
 
@@ -178,6 +181,7 @@ StartupDecodingContext(List *output_plugin_options,
 	ctx->reorder->begin = begin_cb_wrapper;
 	ctx->reorder->apply_change = change_cb_wrapper;
 	ctx->reorder->commit = commit_cb_wrapper;
+	ctx->reorder->message = message_cb_wrapper;
 
 	ctx->out = makeStringInfo();
 	ctx->prepare_write = prepare_write;
@@ -702,6 +706,39 @@ filter_by_origin_cb_wrapper(LogicalDecodingContext *ctx, RepOriginId origin_id)
 	return ret;
 }
 
+static void
+message_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
+				   XLogRecPtr message_lsn, const char *prefix, Size sz,
+				   const char *message)
+{
+	LogicalDecodingContext *ctx = cache->private_data;
+	LogicalErrorCallbackState state;
+	ErrorContextCallback errcallback;
+
+	if (ctx->callbacks.message_cb == NULL)
+		return;
+
+	/* Push callback + info on the error context stack */
+	state.ctx = ctx;
+	state.callback_name = "message";
+	state.report_location = message_lsn;
+	errcallback.callback = output_plugin_error_callback;
+	errcallback.arg = (void *) &state;
+	errcallback.previous = error_context_stack;
+	error_context_stack = &errcallback;
+
+	/* set output state */
+	ctx->accept_writes = true;
+	ctx->write_xid = txn != NULL ? txn->xid : InvalidTransactionId;
+	ctx->write_location = message_lsn;
+
+	/* do the actual work: call callback */
+	ctx->callbacks.message_cb(ctx, txn, message_lsn, prefix, sz, message);
+
+	/* Pop the error context stack */
+	error_context_stack = errcallback.previous;
+}
+
 /*
  * Set the required catalog xmin horizon for historic snapshots in the current
  * replication slot.
diff --git a/src/backend/replication/logical/logicalfuncs.c b/src/backend/replication/logical/logicalfuncs.c
index f789fc1..552dac3 100644
--- a/src/backend/replication/logical/logicalfuncs.c
+++ b/src/backend/replication/logical/logicalfuncs.c
@@ -24,6 +24,8 @@
 #include "access/xlog_internal.h"
 #include "access/xlogutils.h"
 
+#include "access/xact.h"
+
 #include "catalog/pg_type.h"
 
 #include "nodes/makefuncs.h"
@@ -41,6 +43,7 @@
 #include "replication/decode.h"
 #include "replication/logical.h"
 #include "replication/logicalfuncs.h"
+#include "replication/message.h"
 
 #include "storage/fd.h"
 
@@ -363,3 +366,27 @@ pg_logical_slot_peek_binary_changes(PG_FUNCTION_ARGS)
 {
 	return pg_logical_slot_get_changes_guts(fcinfo, false, true);
 }
+
+
+/*
+ * SQL function for writing logical decding message into WAL.
+ */
+Datum
+pg_logical_emit_message_bytea(PG_FUNCTION_ARGS)
+{
+	bool		transactional = PG_GETARG_BOOL(0);
+	char	   *prefix = text_to_cstring(PG_GETARG_TEXT_PP(1));
+	bytea	   *data = PG_GETARG_BYTEA_PP(2);
+	XLogRecPtr	lsn;
+
+	lsn = LogLogicalMessage(prefix, VARDATA_ANY(data), VARSIZE_ANY_EXHDR(data),
+							transactional);
+	PG_RETURN_LSN(lsn);
+}
+
+Datum
+pg_logical_emit_message_text(PG_FUNCTION_ARGS)
+{
+	/* bytea and text are compatible */
+	return pg_logical_emit_message_bytea(fcinfo);
+}
diff --git a/src/backend/replication/logical/message.c b/src/backend/replication/logical/message.c
new file mode 100644
index 0000000..214be45
--- /dev/null
+++ b/src/backend/replication/logical/message.c
@@ -0,0 +1,87 @@
+/*-------------------------------------------------------------------------
+ *
+ * message.c
+ *	  Generic logical messages.
+ *
+ * Copyright (c) 2013-2016, PostgreSQL Global Development Group
+ *
+ * IDENTIFICATION
+ *	  src/backend/replication/logical/message.c
+ *
+ * NOTES
+ *
+ * Generic logical messages allow XLOG logging of arbitrary binary blobs that
+ * get passed to the logical decoding plugin. In normal XLOG processing they
+ * are same as NOOP.
+ *
+ * These messages can be either transactional or non-transactional.
+ * Transactional messages are part of current transaction and will be sent to
+ * decoding plugin using in a same way as DML operations.
+ * Non-transactional messages are sent to the plugin at the time when the
+ * logical decoding reads them from XLOG.
+ *
+ * Every message carries prefix to avoid conflicts between different decoding
+ * plugins. The prefix has to be registered before the message using that
+ * prefix can be written to XLOG. The prefix can be registered exactly once to
+ * avoid situation where multiple third party extensions try to use same
+ * prefix.
+ *
+ * ---------------------------------------------------------------------------
+ */
+
+#include "postgres.h"
+
+#include "access/xact.h"
+
+#include "catalog/indexing.h"
+
+#include "nodes/execnodes.h"
+
+#include "replication/message.h"
+#include "replication/logical.h"
+
+#include "utils/memutils.h"
+
+/*
+ * Write logical decoding message into XLog.
+ */
+XLogRecPtr
+LogLogicalMessage(const char *prefix, const char *message, size_t size,
+				  bool transactional)
+{
+	xl_logical_message	xlrec;
+
+	/*
+	 * Force xid to be allocated if we're emitting a transactional message.
+	 */
+	if (transactional)
+	{
+		Assert(IsTransactionState());
+		GetCurrentTransactionId();
+	}
+
+	xlrec.transactional = transactional;
+	xlrec.prefix_size = strlen(prefix) + 1;
+	xlrec.message_size = size;
+
+	XLogBeginInsert();
+	XLogRegisterData((char *) &xlrec, SizeOfLogicalMessage);
+	XLogRegisterData((char *) prefix, xlrec.prefix_size);
+	XLogRegisterData((char *) message, size);
+
+	return XLogInsert(RM_LOGICALMSG_ID, XLOG_LOGICAL_MESSAGE);
+}
+
+/*
+ * Redo is basically just noop for logical decoding messages.
+ */
+void
+logicalmsg_redo(XLogReaderState *record)
+{
+	uint8		info = XLogRecGetInfo(record) & ~XLR_INFO_MASK;
+
+	if (info != XLOG_LOGICAL_MESSAGE)
+			elog(PANIC, "logicalmsg_redo: unknown op code %u", info);
+
+	/* This is only interesting for logical decoding, see decode.c. */
+}
diff --git a/src/backend/replication/logical/reorderbuffer.c b/src/backend/replication/logical/reorderbuffer.c
index f2b8f4b..d6d436e 100644
--- a/src/backend/replication/logical/reorderbuffer.c
+++ b/src/backend/replication/logical/reorderbuffer.c
@@ -414,6 +414,14 @@ ReorderBufferReturnChange(ReorderBuffer *rb, ReorderBufferChange *change)
 				change->data.tp.oldtuple = NULL;
 			}
 			break;
+		case REORDER_BUFFER_CHANGE_MESSAGE:
+			if (change->data.msg.prefix != NULL)
+				pfree(change->data.msg.prefix);
+			change->data.msg.prefix = NULL;
+			if (change->data.msg.message != NULL)
+				pfree(change->data.msg.message);
+			change->data.msg.message = NULL;
+			break;
 		case REORDER_BUFFER_CHANGE_INTERNAL_SNAPSHOT:
 			if (change->data.snapshot)
 			{
@@ -627,6 +635,28 @@ ReorderBufferQueueChange(ReorderBuffer *rb, TransactionId xid, XLogRecPtr lsn,
 	ReorderBufferCheckSerializeTXN(rb, txn);
 }
 
+/*
+ * Queue message into a transaction so it can be processed upon commit.
+ */
+void
+ReorderBufferQueueMessage(ReorderBuffer *rb, TransactionId xid, XLogRecPtr lsn,
+						  const char *prefix, Size msg_sz, const char *msg)
+{
+	ReorderBufferChange *change;
+
+	Assert(xid != InvalidTransactionId);
+
+	change = ReorderBufferGetChange(rb);
+	change->action = REORDER_BUFFER_CHANGE_MESSAGE;
+	change->data.msg.prefix = pstrdup(prefix);
+	change->data.msg.message_size = msg_sz;
+	change->data.msg.message = palloc(msg_sz);
+	memcpy(change->data.msg.message, msg, msg_sz);
+
+	ReorderBufferQueueChange(rb, xid, lsn, change);
+}
+
+
 static void
 AssertTXNLsnOrder(ReorderBuffer *rb)
 {
@@ -1493,6 +1523,13 @@ ReorderBufferCommit(ReorderBuffer *rb, TransactionId xid,
 					specinsert = change;
 					break;
 
+				case REORDER_BUFFER_CHANGE_MESSAGE:
+					rb->message(rb, txn, change->lsn,
+								change->data.msg.prefix,
+								change->data.msg.message_size,
+								change->data.msg.message);
+					break;
+
 				case REORDER_BUFFER_CHANGE_INTERNAL_SNAPSHOT:
 					/* get rid of the old */
 					TeardownHistoricSnapshot(false);
@@ -2159,6 +2196,21 @@ ReorderBufferSerializeChange(ReorderBuffer *rb, ReorderBufferTXN *txn,
 				}
 				break;
 			}
+		case REORDER_BUFFER_CHANGE_MESSAGE:
+			{
+				char	   *data;
+				size_t		prefix_size = strlen(change->data.msg.prefix) + 1;
+
+				sz += prefix_size + change->data.msg.message_size;
+				ReorderBufferSerializeReserve(rb, sz);
+
+				data = ((char *) rb->outbuf) + sizeof(ReorderBufferDiskChange);
+				memcpy(data, change->data.msg.prefix,
+					   prefix_size);
+				memcpy(data + prefix_size, change->data.msg.message,
+					   change->data.msg.message_size);
+				break;
+			}
 		case REORDER_BUFFER_CHANGE_INTERNAL_SNAPSHOT:
 			{
 				Snapshot	snap;
@@ -2415,6 +2467,22 @@ ReorderBufferRestoreChange(ReorderBuffer *rb, ReorderBufferTXN *txn,
 			}
 
 			break;
+		case REORDER_BUFFER_CHANGE_MESSAGE:
+			{
+				Size		message_size = change->data.msg.message_size;
+				/* prefix includes trailing zero */
+				Size		prefix_size = strlen(data) + 1;
+
+				change->data.msg.prefix = MemoryContextAlloc(rb->context,
+															 prefix_size);
+				memcpy(change->data.msg.prefix, data, prefix_size);
+				data += prefix_size;
+				change->data.msg.message = MemoryContextAlloc(rb->context,
+															  message_size);
+				memcpy(change->data.msg.message, data, message_size);
+				data += message_size;
+				break;
+			}
 		case REORDER_BUFFER_CHANGE_INTERNAL_SNAPSHOT:
 			{
 				Snapshot	oldsnap;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index 179b85a..b4dc617 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -605,6 +605,25 @@ SnapBuildExportSnapshot(SnapBuild *builder)
 }
 
 /*
+ * Ensure there is a snapshot and if not build one for current transaction.
+ */
+Snapshot
+SnapBuildGetOrBuildSnapshot(SnapBuild *builder, TransactionId xid)
+{
+	Assert(builder->state == SNAPBUILD_CONSISTENT);
+
+	/* only build a new snapshot if we don't have a prebuilt one */
+	if (builder->snapshot == NULL)
+	{
+		builder->snapshot = SnapBuildBuildSnapshot(builder, xid);
+		/* inrease refcount for the snapshot builder */
+		SnapBuildSnapIncRefcount(builder->snapshot);
+	}
+
+	return builder->snapshot;
+}
+
+/*
  * Reset a previously SnapBuildExportSnapshot()'ed snapshot if there is
  * any. Aborts the previously started transaction and resets the resource
  * owner back to its original value.
diff --git a/src/bin/pg_xlogdump/rmgrdesc.c b/src/bin/pg_xlogdump/rmgrdesc.c
index f9cd395..6ba7f22 100644
--- a/src/bin/pg_xlogdump/rmgrdesc.c
+++ b/src/bin/pg_xlogdump/rmgrdesc.c
@@ -25,6 +25,7 @@
 #include "commands/dbcommands_xlog.h"
 #include "commands/sequence.h"
 #include "commands/tablespace.h"
+#include "replication/message.h"
 #include "replication/origin.h"
 #include "rmgrdesc.h"
 #include "storage/standbydefs.h"
diff --git a/src/include/access/rmgrlist.h b/src/include/access/rmgrlist.h
index fab912d..35c242d 100644
--- a/src/include/access/rmgrlist.h
+++ b/src/include/access/rmgrlist.h
@@ -45,3 +45,4 @@ PG_RMGR(RM_SPGIST_ID, "SPGist", spg_redo, spg_desc, spg_identify, spg_xlog_start
 PG_RMGR(RM_BRIN_ID, "BRIN", brin_redo, brin_desc, brin_identify, NULL, NULL)
 PG_RMGR(RM_COMMIT_TS_ID, "CommitTs", commit_ts_redo, commit_ts_desc, commit_ts_identify, NULL, NULL)
 PG_RMGR(RM_REPLORIGIN_ID, "ReplicationOrigin", replorigin_redo, replorigin_desc, replorigin_identify, NULL, NULL)
+PG_RMGR(RM_LOGICALMSG_ID, "LogicalMessage", logicalmsg_redo, logicalmsg_desc, logicalmsg_identify, NULL, NULL)
diff --git a/src/include/catalog/pg_proc.h b/src/include/catalog/pg_proc.h
index a595327..3713739 100644
--- a/src/include/catalog/pg_proc.h
+++ b/src/include/catalog/pg_proc.h
@@ -5114,6 +5114,10 @@ DATA(insert OID = 3784 (  pg_logical_slot_peek_changes PGNSP PGUID 12 1000 1000
 DESCR("peek at changes from replication slot");
 DATA(insert OID = 3785 (  pg_logical_slot_peek_binary_changes PGNSP PGUID 12 1000 1000 25 0 f f f f f t v u 4 0 2249 "19 3220 23 1009" "{19,3220,23,1009,3220,28,17}" "{i,i,i,v,o,o,o}" "{slot_name,upto_lsn,upto_nchanges,options,location,xid,data}" _null_ _null_ pg_logical_slot_peek_binary_changes _null_ _null_ _null_ ));
 DESCR("peek at binary changes from replication slot");
+DATA(insert OID = 3577 (  pg_logical_emit_message PGNSP PGUID 12 1 0 0 0 f f f f t f v u 3 0 3220 "16 25 25" _null_ _null_ _null_ _null_ _null_ pg_logical_emit_message_text _null_ _null_ _null_ ));
+DESCR("emit a textual logical decoding message");
+DATA(insert OID = 3578 (  pg_logical_emit_message PGNSP PGUID 12 1 0 0 0 f f f f t f v u 3 0 3220 "16 25 17" _null_ _null_ _null_ _null_ _null_ pg_logical_emit_message_bytea _null_ _null_ _null_ ));
+DESCR("emit a binary logical decoding message");
 
 /* event triggers */
 DATA(insert OID = 3566 (  pg_event_trigger_dropped_objects		PGNSP PGUID 12 10 100 0 0 f f f f t t s s 0 0 2249 "" "{26,26,23,16,16,16,25,25,25,25,1009,1009}" "{o,o,o,o,o,o,o,o,o,o,o,o}" "{classid, objid, objsubid, original, normal, is_temporary, object_type, schema_name, object_name, object_identity, address_names, address_args}" _null_ _null_ pg_event_trigger_dropped_objects _null_ _null_ _null_ ));
diff --git a/src/include/replication/logicalfuncs.h b/src/include/replication/logicalfuncs.h
index c87a1df..5540414 100644
--- a/src/include/replication/logicalfuncs.h
+++ b/src/include/replication/logicalfuncs.h
@@ -21,4 +21,6 @@ extern Datum pg_logical_slot_get_binary_changes(PG_FUNCTION_ARGS);
 extern Datum pg_logical_slot_peek_changes(PG_FUNCTION_ARGS);
 extern Datum pg_logical_slot_peek_binary_changes(PG_FUNCTION_ARGS);
 
+extern Datum pg_logical_emit_message_bytea(PG_FUNCTION_ARGS);
+extern Datum pg_logical_emit_message_text(PG_FUNCTION_ARGS);
 #endif
diff --git a/src/include/replication/message.h b/src/include/replication/message.h
new file mode 100644
index 0000000..b1730c9
--- /dev/null
+++ b/src/include/replication/message.h
@@ -0,0 +1,41 @@
+/*-------------------------------------------------------------------------
+ * message.h
+ *	   Exports from replication/logical/message.c
+ *
+ * Copyright (c) 2013-2016, PostgreSQL Global Development Group
+ *
+ * src/include/replication/message.h
+ *-------------------------------------------------------------------------
+ */
+#ifndef PG_LOGICAL_MESSAGE_H
+#define PG_LOGICAL_MESSAGE_H
+
+#include "access/xlog.h"
+#include "access/xlogdefs.h"
+#include "access/xlogreader.h"
+
+/*
+ * Generic logical decoding message wal record.
+ */
+typedef struct xl_logical_message
+{
+	bool		transactional;					/* is message transactional? */
+	size_t		prefix_size;					/* length of prefix */
+	size_t		message_size;					/* size of the message */
+	char		message[FLEXIBLE_ARRAY_MEMBER];	/* message including the null
+												 * terminated prefx of length
+												 * prefix_size */
+} xl_logical_message;
+
+#define SizeOfLogicalMessage	(offsetof(xl_logical_message, message))
+
+extern XLogRecPtr LogLogicalMessage(const char *prefix, const char *message,
+									size_t size, bool transactional);
+
+/* RMGR API*/
+#define XLOG_LOGICAL_MESSAGE	0x00
+void		logicalmsg_redo(XLogReaderState *record);
+void		logicalmsg_desc(StringInfo buf, XLogReaderState *record);
+const char *logicalmsg_identify(uint8 info);
+
+#endif   /* PG_LOGICAL_MESSAGE_H */
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 577b12e..fb5b758 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -74,6 +74,17 @@ typedef void (*LogicalDecodeCommitCB) (
 												   XLogRecPtr commit_lsn);
 
 /*
+ * Called for the generic logical decoding messages.
+ */
+typedef void (*LogicalDecodeMessageCB) (
+											 struct LogicalDecodingContext *,
+											 ReorderBufferTXN *txn,
+											 XLogRecPtr message_lsn,
+											 const char *prefix,
+											 Size message_size,
+											 const char *message);
+
+/*
  * Filter changes by origin.
  */
 typedef bool (*LogicalDecodeFilterByOriginCB) (
@@ -96,6 +107,7 @@ typedef struct OutputPluginCallbacks
 	LogicalDecodeBeginCB begin_cb;
 	LogicalDecodeChangeCB change_cb;
 	LogicalDecodeCommitCB commit_cb;
+	LogicalDecodeMessageCB message_cb;
 	LogicalDecodeFilterByOriginCB filter_by_origin_cb;
 	LogicalDecodeShutdownCB shutdown_cb;
 } OutputPluginCallbacks;
diff --git a/src/include/replication/reorderbuffer.h b/src/include/replication/reorderbuffer.h
index b52d06a..c12dbf4 100644
--- a/src/include/replication/reorderbuffer.h
+++ b/src/include/replication/reorderbuffer.h
@@ -54,6 +54,7 @@ enum ReorderBufferChangeType
 	REORDER_BUFFER_CHANGE_INSERT,
 	REORDER_BUFFER_CHANGE_UPDATE,
 	REORDER_BUFFER_CHANGE_DELETE,
+	REORDER_BUFFER_CHANGE_MESSAGE,
 	REORDER_BUFFER_CHANGE_INTERNAL_SNAPSHOT,
 	REORDER_BUFFER_CHANGE_INTERNAL_COMMAND_ID,
 	REORDER_BUFFER_CHANGE_INTERNAL_TUPLECID,
@@ -98,6 +99,14 @@ typedef struct ReorderBufferChange
 			ReorderBufferTupleBuf *newtuple;
 		}			tp;
 
+		/* Message with arbitrary data. */
+		struct
+		{
+			char *prefix;
+			size_t message_size;
+			char *message;
+		} msg;
+
 		/* New snapshot, set when action == *_INTERNAL_SNAPSHOT */
 		Snapshot	snapshot;
 
@@ -274,6 +283,14 @@ typedef void (*ReorderBufferCommitCB) (
 												   ReorderBufferTXN *txn,
 												   XLogRecPtr commit_lsn);
 
+/* message callback signature */
+typedef void (*ReorderBufferMessageCB) (
+												   ReorderBuffer *rb,
+												   ReorderBufferTXN *txn,
+												   XLogRecPtr message_lsn,
+												   const char *prefix, Size sz,
+												   const char *message);
+
 struct ReorderBuffer
 {
 	/*
@@ -300,6 +317,7 @@ struct ReorderBuffer
 	ReorderBufferBeginCB begin;
 	ReorderBufferApplyChangeCB apply_change;
 	ReorderBufferCommitCB commit;
+	ReorderBufferMessageCB message;
 
 	/*
 	 * Pointer that will be passed untouched to the callbacks.
@@ -350,6 +368,8 @@ ReorderBufferChange *ReorderBufferGetChange(ReorderBuffer *);
 void		ReorderBufferReturnChange(ReorderBuffer *, ReorderBufferChange *);
 
 void		ReorderBufferQueueChange(ReorderBuffer *, TransactionId, XLogRecPtr lsn, ReorderBufferChange *);
+void		ReorderBufferQueueMessage(ReorderBuffer *, TransactionId, XLogRecPtr lsn,
+									  const char *prefix, Size msg_sz, const char *msg);
 void ReorderBufferCommit(ReorderBuffer *, TransactionId,
 					XLogRecPtr commit_lsn, XLogRecPtr end_lsn,
 	  TimestampTz commit_time, RepOriginId origin_id, XLogRecPtr origin_lsn);
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index 75955af..c4127a1 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -63,6 +63,8 @@ extern const char *SnapBuildExportSnapshot(SnapBuild *snapstate);
 extern void SnapBuildClearExportedSnapshot(void);
 
 extern SnapBuildState SnapBuildCurrentState(SnapBuild *snapstate);
+extern Snapshot SnapBuildGetOrBuildSnapshot(SnapBuild *builder,
+											TransactionId xid);
 
 extern bool SnapBuildXactNeedsSkip(SnapBuild *snapstate, XLogRecPtr ptr);
 
-- 
1.9.1

From f47730e5e8ef5797c7595aafcbf8cff3b375d0ad Mon Sep 17 00:00:00 2001
From: Petr Jelinek <pjmodos@pjmodos.net>
Date: Wed, 24 Feb 2016 17:02:36 +0100
Subject: [PATCH] Logical Decoding Messages

---
 contrib/test_decoding/Makefile                  |  2 +-
 contrib/test_decoding/expected/ddl.out          | 21 ++++--
 contrib/test_decoding/expected/messages.out     | 56 ++++++++++++++++
 contrib/test_decoding/sql/ddl.sql               |  3 +-
 contrib/test_decoding/sql/messages.sql          | 17 +++++
 contrib/test_decoding/test_decoding.c           | 17 +++++
 doc/src/sgml/func.sgml                          | 45 +++++++++++++
 doc/src/sgml/logicaldecoding.sgml               | 34 ++++++++++
 src/backend/access/rmgrdesc/Makefile            |  4 +-
 src/backend/access/rmgrdesc/logicalmsgdesc.c    | 41 ++++++++++++
 src/backend/access/transam/rmgr.c               |  1 +
 src/backend/replication/logical/Makefile        |  2 +-
 src/backend/replication/logical/decode.c        | 49 ++++++++++++++
 src/backend/replication/logical/logical.c       | 37 +++++++++++
 src/backend/replication/logical/logicalfuncs.c  | 27 ++++++++
 src/backend/replication/logical/message.c       | 87 +++++++++++++++++++++++++
 src/backend/replication/logical/reorderbuffer.c | 68 +++++++++++++++++++
 src/backend/replication/logical/snapbuild.c     | 19 ++++++
 src/bin/pg_xlogdump/logicalmsgdesc.c            |  1 +
 src/bin/pg_xlogdump/rmgrdesc.c                  |  1 +
 src/include/access/rmgrlist.h                   |  1 +
 src/include/catalog/pg_proc.h                   |  4 ++
 src/include/replication/logicalfuncs.h          |  2 +
 src/include/replication/message.h               | 41 ++++++++++++
 src/include/replication/output_plugin.h         | 12 ++++
 src/include/replication/reorderbuffer.h         | 20 ++++++
 src/include/replication/snapbuild.h             |  2 +
 27 files changed, 602 insertions(+), 12 deletions(-)
 create mode 100644 contrib/test_decoding/expected/messages.out
 create mode 100644 contrib/test_decoding/sql/messages.sql
 create mode 100644 src/backend/access/rmgrdesc/logicalmsgdesc.c
 create mode 100644 src/backend/replication/logical/message.c
 create mode 120000 src/bin/pg_xlogdump/logicalmsgdesc.c
 create mode 100644 src/include/replication/message.h

diff --git a/contrib/test_decoding/Makefile b/contrib/test_decoding/Makefile
index 06c9546..309cb0b 100644
--- a/contrib/test_decoding/Makefile
+++ b/contrib/test_decoding/Makefile
@@ -38,7 +38,7 @@ submake-test_decoding:
 	$(MAKE) -C $(top_builddir)/contrib/test_decoding
 
 REGRESSCHECKS=ddl xact rewrite toast permissions decoding_in_xact \
-	decoding_into_rel binary prepared replorigin time
+	decoding_into_rel binary prepared replorigin time messages
 
 regresscheck: | submake-regress submake-test_decoding temp-install
 	$(MKDIR_P) regression_output
diff --git a/contrib/test_decoding/expected/ddl.out b/contrib/test_decoding/expected/ddl.out
index 77719e8..32cd24d 100644
--- a/contrib/test_decoding/expected/ddl.out
+++ b/contrib/test_decoding/expected/ddl.out
@@ -220,11 +220,17 @@ SELECT data FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'inc
 (7 rows)
 
 /*
- * check that disk spooling works
+ * check that disk spooling works (also for logical messages)
  */
 BEGIN;
 CREATE TABLE tr_etoomuch (id serial primary key, data int);
 INSERT INTO tr_etoomuch(data) SELECT g.i FROM generate_series(1, 10234) g(i);
+SELECT 'tx logical msg' FROM pg_logical_emit_message(true, 'test', 'tx logical msg');
+    ?column?    
+----------------
+ tx logical msg
+(1 row)
+
 DELETE FROM tr_etoomuch WHERE id < 5000;
 UPDATE tr_etoomuch SET data = - data WHERE id > 5000;
 COMMIT;
@@ -233,12 +239,13 @@ SELECT count(*), min(data), max(data)
 FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'include-xids', '0', 'skip-empty-xacts', '1')
 GROUP BY substring(data, 1, 24)
 ORDER BY 1,2;
- count |                       min                       |                                  max                                   
--------+-------------------------------------------------+------------------------------------------------------------------------
-     1 | BEGIN                                           | BEGIN
-     1 | COMMIT                                          | COMMIT
- 20467 | table public.tr_etoomuch: DELETE: id[integer]:1 | table public.tr_etoomuch: UPDATE: id[integer]:9999 data[integer]:-9999
-(3 rows)
+ count |                                  min                                  |                                  max                                   
+-------+-----------------------------------------------------------------------+------------------------------------------------------------------------
+     1 | BEGIN                                                                 | BEGIN
+     1 | COMMIT                                                                | COMMIT
+     1 | message: transactional: 1 prefix: test, sz: 14 content:tx logical msg | message: transactional: 1 prefix: test, sz: 14 content:tx logical msg
+ 20467 | table public.tr_etoomuch: DELETE: id[integer]:1                       | table public.tr_etoomuch: UPDATE: id[integer]:9999 data[integer]:-9999
+(4 rows)
 
 -- check updates of primary keys work correctly
 BEGIN;
diff --git a/contrib/test_decoding/expected/messages.out b/contrib/test_decoding/expected/messages.out
new file mode 100644
index 0000000..7fa8256
--- /dev/null
+++ b/contrib/test_decoding/expected/messages.out
@@ -0,0 +1,56 @@
+-- predictability
+SET synchronous_commit = on;
+SELECT 'init' FROM pg_create_logical_replication_slot('regression_slot', 'test_decoding');
+ ?column? 
+----------
+ init
+(1 row)
+
+SELECT 'msg1' FROM pg_logical_emit_message(true, 'test', 'msg1');
+ ?column? 
+----------
+ msg1
+(1 row)
+
+SELECT 'msg2' FROM pg_logical_emit_message(false, 'test', 'msg2');
+ ?column? 
+----------
+ msg2
+(1 row)
+
+BEGIN;
+SELECT 'msg3' FROM pg_logical_emit_message(true, 'test', 'msg3');
+ ?column? 
+----------
+ msg3
+(1 row)
+
+SELECT 'msg4' FROM pg_logical_emit_message(false, 'test', 'msg4');
+ ?column? 
+----------
+ msg4
+(1 row)
+
+SELECT 'msg5' FROM pg_logical_emit_message(true, 'test', 'msg5');
+ ?column? 
+----------
+ msg5
+(1 row)
+
+COMMIT;
+SELECT data FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'force-binary', '0', 'skip-empty-xacts', '1');
+                            data                            
+------------------------------------------------------------
+ message: transactional: 1 prefix: test, sz: 4 content:msg1
+ message: transactional: 0 prefix: test, sz: 4 content:msg2
+ message: transactional: 0 prefix: test, sz: 4 content:msg4
+ message: transactional: 1 prefix: test, sz: 4 content:msg3
+ message: transactional: 1 prefix: test, sz: 4 content:msg5
+(5 rows)
+
+SELECT 'init' FROM pg_drop_replication_slot('regression_slot');
+ ?column? 
+----------
+ init
+(1 row)
+
diff --git a/contrib/test_decoding/sql/ddl.sql b/contrib/test_decoding/sql/ddl.sql
index ad928ad..b1f7bf6 100644
--- a/contrib/test_decoding/sql/ddl.sql
+++ b/contrib/test_decoding/sql/ddl.sql
@@ -108,11 +108,12 @@ DELETE FROM tr_pkey;
 SELECT data FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'include-xids', '0', 'skip-empty-xacts', '1');
 
 /*
- * check that disk spooling works
+ * check that disk spooling works (also for logical messages)
  */
 BEGIN;
 CREATE TABLE tr_etoomuch (id serial primary key, data int);
 INSERT INTO tr_etoomuch(data) SELECT g.i FROM generate_series(1, 10234) g(i);
+SELECT 'tx logical msg' FROM pg_logical_emit_message(true, 'test', 'tx logical msg');
 DELETE FROM tr_etoomuch WHERE id < 5000;
 UPDATE tr_etoomuch SET data = - data WHERE id > 5000;
 COMMIT;
diff --git a/contrib/test_decoding/sql/messages.sql b/contrib/test_decoding/sql/messages.sql
new file mode 100644
index 0000000..8744eb6
--- /dev/null
+++ b/contrib/test_decoding/sql/messages.sql
@@ -0,0 +1,17 @@
+-- predictability
+SET synchronous_commit = on;
+
+SELECT 'init' FROM pg_create_logical_replication_slot('regression_slot', 'test_decoding');
+
+SELECT 'msg1' FROM pg_logical_emit_message(true, 'test', 'msg1');
+SELECT 'msg2' FROM pg_logical_emit_message(false, 'test', 'msg2');
+
+BEGIN;
+SELECT 'msg3' FROM pg_logical_emit_message(true, 'test', 'msg3');
+SELECT 'msg4' FROM pg_logical_emit_message(false, 'test', 'msg4');
+SELECT 'msg5' FROM pg_logical_emit_message(true, 'test', 'msg5');
+COMMIT;
+
+SELECT data FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'force-binary', '0', 'skip-empty-xacts', '1');
+
+SELECT 'init' FROM pg_drop_replication_slot('regression_slot');
diff --git a/contrib/test_decoding/test_decoding.c b/contrib/test_decoding/test_decoding.c
index 4cf808f..1997774 100644
--- a/contrib/test_decoding/test_decoding.c
+++ b/contrib/test_decoding/test_decoding.c
@@ -21,6 +21,7 @@
 
 #include "replication/output_plugin.h"
 #include "replication/logical.h"
+#include "replication/message.h"
 #include "replication/origin.h"
 
 #include "utils/builtins.h"
@@ -63,6 +64,9 @@ static void pg_decode_change(LogicalDecodingContext *ctx,
 				 ReorderBufferChange *change);
 static bool pg_decode_filter(LogicalDecodingContext *ctx,
 				 RepOriginId origin_id);
+static void pg_decode_message(LogicalDecodingContext *ctx,
+							  ReorderBufferTXN *txn, XLogRecPtr message_lsn,
+							  const char *prefix, Size sz, const char *message);
 
 void
 _PG_init(void)
@@ -82,6 +86,7 @@ _PG_output_plugin_init(OutputPluginCallbacks *cb)
 	cb->commit_cb = pg_decode_commit_txn;
 	cb->filter_by_origin_cb = pg_decode_filter;
 	cb->shutdown_cb = pg_decode_shutdown;
+	cb->message_cb = pg_decode_message;
 }
 
 
@@ -471,3 +476,15 @@ pg_decode_change(LogicalDecodingContext *ctx, ReorderBufferTXN *txn,
 
 	OutputPluginWrite(ctx, true);
 }
+
+static void
+pg_decode_message(LogicalDecodingContext *ctx,
+				  ReorderBufferTXN *txn, XLogRecPtr lsn,
+				  const char *prefix, Size sz, const char *message)
+{
+	OutputPluginPrepareWrite(ctx, true);
+	appendStringInfo(ctx->out, "message: transactional: %d prefix: %s, sz: %zu content:",
+					 txn != NULL, prefix, sz);
+	appendBinaryStringInfo(ctx->out, message, sz);
+	OutputPluginWrite(ctx, true);
+}
diff --git a/doc/src/sgml/func.sgml b/doc/src/sgml/func.sgml
index ae93e69..02f556b 100644
--- a/doc/src/sgml/func.sgml
+++ b/doc/src/sgml/func.sgml
@@ -18238,6 +18238,51 @@ postgres=# SELECT * FROM pg_xlogfile_name_offset(pg_stop_backup());
        </entry>
       </row>
 
+      <row>
+       <entry id="pg-logical-emit-message-text">
+        <indexterm>
+         <primary>pg_logical_emit_message</primary>
+        </indexterm>
+        <literal><function>pg_logical_emit_message(<parameter>transactional</parameter> <type>bool</type>, <parameter>prefix</parameter> <type>text</type>, <parameter>content</parameter> <type>text</type>)</function></literal>
+       </entry>
+       <entry>
+        void
+       </entry>
+       <entry>
+        Write text logical decoding message. This can be used to pass generic
+        messages to logical decoding plugins through WAL. The parameter
+        <parameter>transactional</parameter> specifies if the message should
+        be part of current transaction or if it should be written immediately
+        and decoded as soon as the logical decoding reads the record. The
+        <parameter>prefix</parameter> is textual prefix used by the logical
+        decoding plugins to easily recognize interesting messages for them.
+        The <parameter>content</parameter> is the text of the message.
+       </entry>
+      </row>
+
+      <row>
+       <entry id="pg-logical-emit-message-bytea">
+        <indexterm>
+         <primary>>pg_logical_emit_message</primary>
+        </indexterm>
+        <literal><function>>pg_logical_emit_message(<parameter>transactional</parameter> <type>bool</type>, <parameter>prefix</parameter> <type>text</type>, <parameter>content</parameter> <type>bytea</type>)</function></literal>
+       </entry>
+       <entry>
+        void
+       </entry>
+       <entry>
+        Write binary logical decoding message. This can be used to pass generic
+        messages to logical decoding plugins through WAL. The parameter
+        <parameter>transactional</parameter> specifies if the message should
+        be part of current transaction or if it should be written immediately
+        and decoded as soon as the logical decoding reads the record. The
+        <parameter>prefix</parameter> is textual prefix used by the logical
+        decoding plugins to easily recognize interesting messages for them.
+        The <parameter>content</parameter> is the binary content of the
+        message.
+       </entry>
+      </row>
+
      </tbody>
     </tgroup>
    </table>
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 45fdfeb..7c9d03a 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -363,6 +363,7 @@ typedef struct OutputPluginCallbacks
     LogicalDecodeBeginCB begin_cb;
     LogicalDecodeChangeCB change_cb;
     LogicalDecodeCommitCB commit_cb;
+    LogicalDecodeMessageCB message_cb;
     LogicalDecodeFilterByOriginCB filter_by_origin_cb;
     LogicalDecodeShutdownCB shutdown_cb;
 } OutputPluginCallbacks;
@@ -602,6 +603,39 @@ typedef bool (*LogicalDecodeFilterByOriginCB) (
        more efficient.
      </para>
      </sect3>
+
+    <sect3 id="logicaldecoding-output-plugin-message">
+     <title>Generic Message Callback</title>
+
+     <para>
+      The optional <function>message_cb</function> callback is called whenever
+      a logical decoding message has been decoded.
+<programlisting>
+typedef void (*LogicalDecodeMessageCB) (
+    struct LogicalDecodingContext *,
+    ReorderBufferTXN *txn,
+    XLogRecPtr message_lsn,
+    const char *prefix,
+    Size message_size,
+    const char *message
+);
+</programlisting>
+      The <parameter>ctx</parameter> and <parameter>txn</parameter> parameters
+      have the same contents as for the <function>begin_cb</function> with the
+      difference that <parameter>txn</parameter> is null for non-transactional
+      messages. The <parameter>lsn</parameter> has WAL position of the message.
+      The <parameter>prefix</parameter> is arbitrary textual prefix which can
+      be used for identifying interesting messages for the current plugin.
+      And finally the <parameter>message</parameter> parameter holds the
+      actual message of <parameter>message_size</parameter> size.
+     </para>
+     <para>
+      Extra care should be taken to ensure that the prefix the output plugin
+      considers interesting is unique. Using name of the extension or the
+      output plugin itself is often a good choice.
+     </para>
+    </sect3>
+
    </sect2>
 
    <sect2 id="logicaldecoding-output-plugin-output">
diff --git a/src/backend/access/rmgrdesc/Makefile b/src/backend/access/rmgrdesc/Makefile
index c72a1f2..723b4d8 100644
--- a/src/backend/access/rmgrdesc/Makefile
+++ b/src/backend/access/rmgrdesc/Makefile
@@ -9,8 +9,8 @@ top_builddir = ../../../..
 include $(top_builddir)/src/Makefile.global
 
 OBJS = brindesc.o clogdesc.o committsdesc.o dbasedesc.o gindesc.o gistdesc.o \
-	   hashdesc.o heapdesc.o mxactdesc.o nbtdesc.o relmapdesc.o \
-	   replorigindesc.o seqdesc.o smgrdesc.o spgdesc.o \
+	   hashdesc.o heapdesc.o logicalmsgdesc.o mxactdesc.o nbtdesc.o \
+	   relmapdesc.o replorigindesc.o seqdesc.o smgrdesc.o spgdesc.o \
 	   standbydesc.o tblspcdesc.o xactdesc.o xlogdesc.o
 
 include $(top_srcdir)/src/backend/common.mk
diff --git a/src/backend/access/rmgrdesc/logicalmsgdesc.c b/src/backend/access/rmgrdesc/logicalmsgdesc.c
new file mode 100644
index 0000000..b194e14
--- /dev/null
+++ b/src/backend/access/rmgrdesc/logicalmsgdesc.c
@@ -0,0 +1,41 @@
+/*-------------------------------------------------------------------------
+ *
+ * logicalmsgdesc.c
+ *	  rmgr descriptor routines for replication/logical/message.c
+ *
+ * Portions Copyright (c) 2015-2016, PostgreSQL Global Development Group
+ *
+ *
+ * IDENTIFICATION
+ *	  src/backend/access/rmgrdesc/logicalmsgdesc.c
+ *
+ *-------------------------------------------------------------------------
+ */
+#include "postgres.h"
+
+#include "replication/message.h"
+
+void
+logicalmsg_desc(StringInfo buf, XLogReaderState *record)
+{
+	char	   *rec = XLogRecGetData(record);
+	uint8		info = XLogRecGetInfo(record) & ~XLR_INFO_MASK;
+
+	if (info == XLOG_LOGICAL_MESSAGE)
+	{
+		xl_logical_message *xlrec = (xl_logical_message *) rec;
+
+		appendStringInfo(buf, "%s message size %zu bytes",
+				   xlrec->transactional ? "transactional" : "nontransactional",
+						 xlrec->message_size);
+	}
+}
+
+const char *
+logicalmsg_identify(uint8 info)
+{
+	if ((info & ~XLR_INFO_MASK) == XLOG_LOGICAL_MESSAGE)
+		return "MESSAGE";
+
+	return NULL;
+}
diff --git a/src/backend/access/transam/rmgr.c b/src/backend/access/transam/rmgr.c
index 7c4d773..1a42121 100644
--- a/src/backend/access/transam/rmgr.c
+++ b/src/backend/access/transam/rmgr.c
@@ -23,6 +23,7 @@
 #include "commands/dbcommands_xlog.h"
 #include "commands/sequence.h"
 #include "commands/tablespace.h"
+#include "replication/message.h"
 #include "replication/origin.h"
 #include "storage/standby.h"
 #include "utils/relmapper.h"
diff --git a/src/backend/replication/logical/Makefile b/src/backend/replication/logical/Makefile
index 8adea13..1d7ca06 100644
--- a/src/backend/replication/logical/Makefile
+++ b/src/backend/replication/logical/Makefile
@@ -14,7 +14,7 @@ include $(top_builddir)/src/Makefile.global
 
 override CPPFLAGS := -I$(srcdir) $(CPPFLAGS)
 
-OBJS = decode.o logical.o logicalfuncs.o reorderbuffer.o origin.o \
+OBJS = decode.o logical.o logicalfuncs.o message.o origin.o reorderbuffer.o \
 	snapbuild.o
 
 include $(top_srcdir)/src/backend/common.mk
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index 13af485..98ec5d9 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -39,6 +39,7 @@
 
 #include "replication/decode.h"
 #include "replication/logical.h"
+#include "replication/message.h"
 #include "replication/reorderbuffer.h"
 #include "replication/origin.h"
 #include "replication/snapbuild.h"
@@ -58,6 +59,7 @@ static void DecodeHeapOp(LogicalDecodingContext *ctx, XLogRecordBuffer *buf);
 static void DecodeHeap2Op(LogicalDecodingContext *ctx, XLogRecordBuffer *buf);
 static void DecodeXactOp(LogicalDecodingContext *ctx, XLogRecordBuffer *buf);
 static void DecodeStandbyOp(LogicalDecodingContext *ctx, XLogRecordBuffer *buf);
+static void DecodeLogicalMsgOp(LogicalDecodingContext *ctx, XLogRecordBuffer *buf);
 
 /* individual record(group)'s handlers */
 static void DecodeInsert(LogicalDecodingContext *ctx, XLogRecordBuffer *buf);
@@ -123,6 +125,10 @@ LogicalDecodingProcessRecord(LogicalDecodingContext *ctx, XLogReaderState *recor
 			DecodeHeapOp(ctx, &buf);
 			break;
 
+		case RM_LOGICALMSG_ID:
+			DecodeLogicalMsgOp(ctx, &buf);
+			break;
+
 			/*
 			 * Rmgrs irrelevant for logical decoding; they describe stuff not
 			 * represented in logical decoding. Add new rmgrs in rmgrlist.h's
@@ -457,6 +463,49 @@ DecodeHeapOp(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
 	}
 }
 
+/*
+ * Handle rmgr LOGICALMSG_ID records for DecodeRecordIntoReorderBuffer().
+ */
+static void
+DecodeLogicalMsgOp(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
+{
+	SnapBuild  *builder = ctx->snapshot_builder;
+	XLogReaderState *r = buf->record;
+	uint8		info = XLogRecGetInfo(r) & ~XLR_INFO_MASK;
+	xl_logical_message *message;
+
+	if (info != XLOG_LOGICAL_MESSAGE)
+		elog(ERROR, "unexpected RM_LOGICALMSG_ID record type: %u", info);
+
+	message = (xl_logical_message *) XLogRecGetData(r);
+
+	if (message->transactional)
+	{
+		if (!SnapBuildProcessChange(builder, XLogRecGetXid(r), buf->origptr))
+			return;
+
+		ReorderBufferQueueMessage(ctx->reorder, XLogRecGetXid(r),
+								  buf->endptr,
+								  message->message, /* first part of message is prefix */
+								  message->message_size,
+								  message->message + message->prefix_size);
+	}
+	else if (SnapBuildCurrentState(builder) == SNAPBUILD_CONSISTENT &&
+			 !SnapBuildXactNeedsSkip(builder, buf->origptr))
+	{
+		volatile Snapshot	snapshot_now;
+		ReorderBuffer	   *rb = ctx->reorder;
+
+		/* setup snapshot to allow catalog access */
+		snapshot_now = SnapBuildGetOrBuildSnapshot(builder, XLogRecGetXid(r));
+		SetupHistoricSnapshot(snapshot_now, NULL);
+		rb->message(rb, NULL, buf->origptr, message->message,
+					message->message_size,
+					message->message + message->prefix_size);
+		TeardownHistoricSnapshot(false);
+	}
+}
+
 static inline bool
 FilterByOrigin(LogicalDecodingContext *ctx, RepOriginId origin_id)
 {
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index 2e6d3f9..7863d52 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -62,6 +62,9 @@ static void commit_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
 				  XLogRecPtr commit_lsn);
 static void change_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
 				  Relation relation, ReorderBufferChange *change);
+static void message_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
+				  XLogRecPtr message_lsn, const char *prefix, Size sz,
+				  const char *message);
 
 static void LoadOutputPlugin(OutputPluginCallbacks *callbacks, char *plugin);
 
@@ -178,6 +181,7 @@ StartupDecodingContext(List *output_plugin_options,
 	ctx->reorder->begin = begin_cb_wrapper;
 	ctx->reorder->apply_change = change_cb_wrapper;
 	ctx->reorder->commit = commit_cb_wrapper;
+	ctx->reorder->message = message_cb_wrapper;
 
 	ctx->out = makeStringInfo();
 	ctx->prepare_write = prepare_write;
@@ -702,6 +706,39 @@ filter_by_origin_cb_wrapper(LogicalDecodingContext *ctx, RepOriginId origin_id)
 	return ret;
 }
 
+static void
+message_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
+				   XLogRecPtr message_lsn, const char *prefix, Size sz,
+				   const char *message)
+{
+	LogicalDecodingContext *ctx = cache->private_data;
+	LogicalErrorCallbackState state;
+	ErrorContextCallback errcallback;
+
+	if (ctx->callbacks.message_cb == NULL)
+		return;
+
+	/* Push callback + info on the error context stack */
+	state.ctx = ctx;
+	state.callback_name = "message";
+	state.report_location = message_lsn;
+	errcallback.callback = output_plugin_error_callback;
+	errcallback.arg = (void *) &state;
+	errcallback.previous = error_context_stack;
+	error_context_stack = &errcallback;
+
+	/* set output state */
+	ctx->accept_writes = true;
+	ctx->write_xid = txn != NULL ? txn->xid : InvalidTransactionId;
+	ctx->write_location = message_lsn;
+
+	/* do the actual work: call callback */
+	ctx->callbacks.message_cb(ctx, txn, message_lsn, prefix, sz, message);
+
+	/* Pop the error context stack */
+	error_context_stack = errcallback.previous;
+}
+
 /*
  * Set the required catalog xmin horizon for historic snapshots in the current
  * replication slot.
diff --git a/src/backend/replication/logical/logicalfuncs.c b/src/backend/replication/logical/logicalfuncs.c
index f789fc1..552dac3 100644
--- a/src/backend/replication/logical/logicalfuncs.c
+++ b/src/backend/replication/logical/logicalfuncs.c
@@ -24,6 +24,8 @@
 #include "access/xlog_internal.h"
 #include "access/xlogutils.h"
 
+#include "access/xact.h"
+
 #include "catalog/pg_type.h"
 
 #include "nodes/makefuncs.h"
@@ -41,6 +43,7 @@
 #include "replication/decode.h"
 #include "replication/logical.h"
 #include "replication/logicalfuncs.h"
+#include "replication/message.h"
 
 #include "storage/fd.h"
 
@@ -363,3 +366,27 @@ pg_logical_slot_peek_binary_changes(PG_FUNCTION_ARGS)
 {
 	return pg_logical_slot_get_changes_guts(fcinfo, false, true);
 }
+
+
+/*
+ * SQL function for writing logical decding message into WAL.
+ */
+Datum
+pg_logical_emit_message_bytea(PG_FUNCTION_ARGS)
+{
+	bool		transactional = PG_GETARG_BOOL(0);
+	char	   *prefix = text_to_cstring(PG_GETARG_TEXT_PP(1));
+	bytea	   *data = PG_GETARG_BYTEA_PP(2);
+	XLogRecPtr	lsn;
+
+	lsn = LogLogicalMessage(prefix, VARDATA_ANY(data), VARSIZE_ANY_EXHDR(data),
+							transactional);
+	PG_RETURN_LSN(lsn);
+}
+
+Datum
+pg_logical_emit_message_text(PG_FUNCTION_ARGS)
+{
+	/* bytea and text are compatible */
+	return pg_logical_emit_message_bytea(fcinfo);
+}
diff --git a/src/backend/replication/logical/message.c b/src/backend/replication/logical/message.c
new file mode 100644
index 0000000..214be45
--- /dev/null
+++ b/src/backend/replication/logical/message.c
@@ -0,0 +1,87 @@
+/*-------------------------------------------------------------------------
+ *
+ * message.c
+ *	  Generic logical messages.
+ *
+ * Copyright (c) 2013-2016, PostgreSQL Global Development Group
+ *
+ * IDENTIFICATION
+ *	  src/backend/replication/logical/message.c
+ *
+ * NOTES
+ *
+ * Generic logical messages allow XLOG logging of arbitrary binary blobs that
+ * get passed to the logical decoding plugin. In normal XLOG processing they
+ * are same as NOOP.
+ *
+ * These messages can be either transactional or non-transactional.
+ * Transactional messages are part of current transaction and will be sent to
+ * decoding plugin using in a same way as DML operations.
+ * Non-transactional messages are sent to the plugin at the time when the
+ * logical decoding reads them from XLOG.
+ *
+ * Every message carries prefix to avoid conflicts between different decoding
+ * plugins. The prefix has to be registered before the message using that
+ * prefix can be written to XLOG. The prefix can be registered exactly once to
+ * avoid situation where multiple third party extensions try to use same
+ * prefix.
+ *
+ * ---------------------------------------------------------------------------
+ */
+
+#include "postgres.h"
+
+#include "access/xact.h"
+
+#include "catalog/indexing.h"
+
+#include "nodes/execnodes.h"
+
+#include "replication/message.h"
+#include "replication/logical.h"
+
+#include "utils/memutils.h"
+
+/*
+ * Write logical decoding message into XLog.
+ */
+XLogRecPtr
+LogLogicalMessage(const char *prefix, const char *message, size_t size,
+				  bool transactional)
+{
+	xl_logical_message	xlrec;
+
+	/*
+	 * Force xid to be allocated if we're emitting a transactional message.
+	 */
+	if (transactional)
+	{
+		Assert(IsTransactionState());
+		GetCurrentTransactionId();
+	}
+
+	xlrec.transactional = transactional;
+	xlrec.prefix_size = strlen(prefix) + 1;
+	xlrec.message_size = size;
+
+	XLogBeginInsert();
+	XLogRegisterData((char *) &xlrec, SizeOfLogicalMessage);
+	XLogRegisterData((char *) prefix, xlrec.prefix_size);
+	XLogRegisterData((char *) message, size);
+
+	return XLogInsert(RM_LOGICALMSG_ID, XLOG_LOGICAL_MESSAGE);
+}
+
+/*
+ * Redo is basically just noop for logical decoding messages.
+ */
+void
+logicalmsg_redo(XLogReaderState *record)
+{
+	uint8		info = XLogRecGetInfo(record) & ~XLR_INFO_MASK;
+
+	if (info != XLOG_LOGICAL_MESSAGE)
+			elog(PANIC, "logicalmsg_redo: unknown op code %u", info);
+
+	/* This is only interesting for logical decoding, see decode.c. */
+}
diff --git a/src/backend/replication/logical/reorderbuffer.c b/src/backend/replication/logical/reorderbuffer.c
index f2b8f4b..d6d436e 100644
--- a/src/backend/replication/logical/reorderbuffer.c
+++ b/src/backend/replication/logical/reorderbuffer.c
@@ -414,6 +414,14 @@ ReorderBufferReturnChange(ReorderBuffer *rb, ReorderBufferChange *change)
 				change->data.tp.oldtuple = NULL;
 			}
 			break;
+		case REORDER_BUFFER_CHANGE_MESSAGE:
+			if (change->data.msg.prefix != NULL)
+				pfree(change->data.msg.prefix);
+			change->data.msg.prefix = NULL;
+			if (change->data.msg.message != NULL)
+				pfree(change->data.msg.message);
+			change->data.msg.message = NULL;
+			break;
 		case REORDER_BUFFER_CHANGE_INTERNAL_SNAPSHOT:
 			if (change->data.snapshot)
 			{
@@ -627,6 +635,28 @@ ReorderBufferQueueChange(ReorderBuffer *rb, TransactionId xid, XLogRecPtr lsn,
 	ReorderBufferCheckSerializeTXN(rb, txn);
 }
 
+/*
+ * Queue message into a transaction so it can be processed upon commit.
+ */
+void
+ReorderBufferQueueMessage(ReorderBuffer *rb, TransactionId xid, XLogRecPtr lsn,
+						  const char *prefix, Size msg_sz, const char *msg)
+{
+	ReorderBufferChange *change;
+
+	Assert(xid != InvalidTransactionId);
+
+	change = ReorderBufferGetChange(rb);
+	change->action = REORDER_BUFFER_CHANGE_MESSAGE;
+	change->data.msg.prefix = pstrdup(prefix);
+	change->data.msg.message_size = msg_sz;
+	change->data.msg.message = palloc(msg_sz);
+	memcpy(change->data.msg.message, msg, msg_sz);
+
+	ReorderBufferQueueChange(rb, xid, lsn, change);
+}
+
+
 static void
 AssertTXNLsnOrder(ReorderBuffer *rb)
 {
@@ -1493,6 +1523,13 @@ ReorderBufferCommit(ReorderBuffer *rb, TransactionId xid,
 					specinsert = change;
 					break;
 
+				case REORDER_BUFFER_CHANGE_MESSAGE:
+					rb->message(rb, txn, change->lsn,
+								change->data.msg.prefix,
+								change->data.msg.message_size,
+								change->data.msg.message);
+					break;
+
 				case REORDER_BUFFER_CHANGE_INTERNAL_SNAPSHOT:
 					/* get rid of the old */
 					TeardownHistoricSnapshot(false);
@@ -2159,6 +2196,21 @@ ReorderBufferSerializeChange(ReorderBuffer *rb, ReorderBufferTXN *txn,
 				}
 				break;
 			}
+		case REORDER_BUFFER_CHANGE_MESSAGE:
+			{
+				char	   *data;
+				size_t		prefix_size = strlen(change->data.msg.prefix) + 1;
+
+				sz += prefix_size + change->data.msg.message_size;
+				ReorderBufferSerializeReserve(rb, sz);
+
+				data = ((char *) rb->outbuf) + sizeof(ReorderBufferDiskChange);
+				memcpy(data, change->data.msg.prefix,
+					   prefix_size);
+				memcpy(data + prefix_size, change->data.msg.message,
+					   change->data.msg.message_size);
+				break;
+			}
 		case REORDER_BUFFER_CHANGE_INTERNAL_SNAPSHOT:
 			{
 				Snapshot	snap;
@@ -2415,6 +2467,22 @@ ReorderBufferRestoreChange(ReorderBuffer *rb, ReorderBufferTXN *txn,
 			}
 
 			break;
+		case REORDER_BUFFER_CHANGE_MESSAGE:
+			{
+				Size		message_size = change->data.msg.message_size;
+				/* prefix includes trailing zero */
+				Size		prefix_size = strlen(data) + 1;
+
+				change->data.msg.prefix = MemoryContextAlloc(rb->context,
+															 prefix_size);
+				memcpy(change->data.msg.prefix, data, prefix_size);
+				data += prefix_size;
+				change->data.msg.message = MemoryContextAlloc(rb->context,
+															  message_size);
+				memcpy(change->data.msg.message, data, message_size);
+				data += message_size;
+				break;
+			}
 		case REORDER_BUFFER_CHANGE_INTERNAL_SNAPSHOT:
 			{
 				Snapshot	oldsnap;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index 179b85a..b4dc617 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -605,6 +605,25 @@ SnapBuildExportSnapshot(SnapBuild *builder)
 }
 
 /*
+ * Ensure there is a snapshot and if not build one for current transaction.
+ */
+Snapshot
+SnapBuildGetOrBuildSnapshot(SnapBuild *builder, TransactionId xid)
+{
+	Assert(builder->state == SNAPBUILD_CONSISTENT);
+
+	/* only build a new snapshot if we don't have a prebuilt one */
+	if (builder->snapshot == NULL)
+	{
+		builder->snapshot = SnapBuildBuildSnapshot(builder, xid);
+		/* inrease refcount for the snapshot builder */
+		SnapBuildSnapIncRefcount(builder->snapshot);
+	}
+
+	return builder->snapshot;
+}
+
+/*
  * Reset a previously SnapBuildExportSnapshot()'ed snapshot if there is
  * any. Aborts the previously started transaction and resets the resource
  * owner back to its original value.
diff --git a/src/bin/pg_xlogdump/logicalmsgdesc.c b/src/bin/pg_xlogdump/logicalmsgdesc.c
new file mode 120000
index 0000000..541fd5e
--- /dev/null
+++ b/src/bin/pg_xlogdump/logicalmsgdesc.c
@@ -0,0 +1 @@
+../../../src/backend/access/rmgrdesc/logicalmsgdesc.c
\ No newline at end of file
diff --git a/src/bin/pg_xlogdump/rmgrdesc.c b/src/bin/pg_xlogdump/rmgrdesc.c
index f9cd395..6ba7f22 100644
--- a/src/bin/pg_xlogdump/rmgrdesc.c
+++ b/src/bin/pg_xlogdump/rmgrdesc.c
@@ -25,6 +25,7 @@
 #include "commands/dbcommands_xlog.h"
 #include "commands/sequence.h"
 #include "commands/tablespace.h"
+#include "replication/message.h"
 #include "replication/origin.h"
 #include "rmgrdesc.h"
 #include "storage/standbydefs.h"
diff --git a/src/include/access/rmgrlist.h b/src/include/access/rmgrlist.h
index fab912d..35c242d 100644
--- a/src/include/access/rmgrlist.h
+++ b/src/include/access/rmgrlist.h
@@ -45,3 +45,4 @@ PG_RMGR(RM_SPGIST_ID, "SPGist", spg_redo, spg_desc, spg_identify, spg_xlog_start
 PG_RMGR(RM_BRIN_ID, "BRIN", brin_redo, brin_desc, brin_identify, NULL, NULL)
 PG_RMGR(RM_COMMIT_TS_ID, "CommitTs", commit_ts_redo, commit_ts_desc, commit_ts_identify, NULL, NULL)
 PG_RMGR(RM_REPLORIGIN_ID, "ReplicationOrigin", replorigin_redo, replorigin_desc, replorigin_identify, NULL, NULL)
+PG_RMGR(RM_LOGICALMSG_ID, "LogicalMessage", logicalmsg_redo, logicalmsg_desc, logicalmsg_identify, NULL, NULL)
diff --git a/src/include/catalog/pg_proc.h b/src/include/catalog/pg_proc.h
index a595327..3713739 100644
--- a/src/include/catalog/pg_proc.h
+++ b/src/include/catalog/pg_proc.h
@@ -5114,6 +5114,10 @@ DATA(insert OID = 3784 (  pg_logical_slot_peek_changes PGNSP PGUID 12 1000 1000
 DESCR("peek at changes from replication slot");
 DATA(insert OID = 3785 (  pg_logical_slot_peek_binary_changes PGNSP PGUID 12 1000 1000 25 0 f f f f f t v u 4 0 2249 "19 3220 23 1009" "{19,3220,23,1009,3220,28,17}" "{i,i,i,v,o,o,o}" "{slot_name,upto_lsn,upto_nchanges,options,location,xid,data}" _null_ _null_ pg_logical_slot_peek_binary_changes _null_ _null_ _null_ ));
 DESCR("peek at binary changes from replication slot");
+DATA(insert OID = 3577 (  pg_logical_emit_message PGNSP PGUID 12 1 0 0 0 f f f f t f v u 3 0 3220 "16 25 25" _null_ _null_ _null_ _null_ _null_ pg_logical_emit_message_text _null_ _null_ _null_ ));
+DESCR("emit a textual logical decoding message");
+DATA(insert OID = 3578 (  pg_logical_emit_message PGNSP PGUID 12 1 0 0 0 f f f f t f v u 3 0 3220 "16 25 17" _null_ _null_ _null_ _null_ _null_ pg_logical_emit_message_bytea _null_ _null_ _null_ ));
+DESCR("emit a binary logical decoding message");
 
 /* event triggers */
 DATA(insert OID = 3566 (  pg_event_trigger_dropped_objects		PGNSP PGUID 12 10 100 0 0 f f f f t t s s 0 0 2249 "" "{26,26,23,16,16,16,25,25,25,25,1009,1009}" "{o,o,o,o,o,o,o,o,o,o,o,o}" "{classid, objid, objsubid, original, normal, is_temporary, object_type, schema_name, object_name, object_identity, address_names, address_args}" _null_ _null_ pg_event_trigger_dropped_objects _null_ _null_ _null_ ));
diff --git a/src/include/replication/logicalfuncs.h b/src/include/replication/logicalfuncs.h
index c87a1df..5540414 100644
--- a/src/include/replication/logicalfuncs.h
+++ b/src/include/replication/logicalfuncs.h
@@ -21,4 +21,6 @@ extern Datum pg_logical_slot_get_binary_changes(PG_FUNCTION_ARGS);
 extern Datum pg_logical_slot_peek_changes(PG_FUNCTION_ARGS);
 extern Datum pg_logical_slot_peek_binary_changes(PG_FUNCTION_ARGS);
 
+extern Datum pg_logical_emit_message_bytea(PG_FUNCTION_ARGS);
+extern Datum pg_logical_emit_message_text(PG_FUNCTION_ARGS);
 #endif
diff --git a/src/include/replication/message.h b/src/include/replication/message.h
new file mode 100644
index 0000000..b1730c9
--- /dev/null
+++ b/src/include/replication/message.h
@@ -0,0 +1,41 @@
+/*-------------------------------------------------------------------------
+ * message.h
+ *	   Exports from replication/logical/message.c
+ *
+ * Copyright (c) 2013-2016, PostgreSQL Global Development Group
+ *
+ * src/include/replication/message.h
+ *-------------------------------------------------------------------------
+ */
+#ifndef PG_LOGICAL_MESSAGE_H
+#define PG_LOGICAL_MESSAGE_H
+
+#include "access/xlog.h"
+#include "access/xlogdefs.h"
+#include "access/xlogreader.h"
+
+/*
+ * Generic logical decoding message wal record.
+ */
+typedef struct xl_logical_message
+{
+	bool		transactional;					/* is message transactional? */
+	size_t		prefix_size;					/* length of prefix */
+	size_t		message_size;					/* size of the message */
+	char		message[FLEXIBLE_ARRAY_MEMBER];	/* message including the null
+												 * terminated prefx of length
+												 * prefix_size */
+} xl_logical_message;
+
+#define SizeOfLogicalMessage	(offsetof(xl_logical_message, message))
+
+extern XLogRecPtr LogLogicalMessage(const char *prefix, const char *message,
+									size_t size, bool transactional);
+
+/* RMGR API*/
+#define XLOG_LOGICAL_MESSAGE	0x00
+void		logicalmsg_redo(XLogReaderState *record);
+void		logicalmsg_desc(StringInfo buf, XLogReaderState *record);
+const char *logicalmsg_identify(uint8 info);
+
+#endif   /* PG_LOGICAL_MESSAGE_H */
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 577b12e..fb5b758 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -74,6 +74,17 @@ typedef void (*LogicalDecodeCommitCB) (
 												   XLogRecPtr commit_lsn);
 
 /*
+ * Called for the generic logical decoding messages.
+ */
+typedef void (*LogicalDecodeMessageCB) (
+											 struct LogicalDecodingContext *,
+											 ReorderBufferTXN *txn,
+											 XLogRecPtr message_lsn,
+											 const char *prefix,
+											 Size message_size,
+											 const char *message);
+
+/*
  * Filter changes by origin.
  */
 typedef bool (*LogicalDecodeFilterByOriginCB) (
@@ -96,6 +107,7 @@ typedef struct OutputPluginCallbacks
 	LogicalDecodeBeginCB begin_cb;
 	LogicalDecodeChangeCB change_cb;
 	LogicalDecodeCommitCB commit_cb;
+	LogicalDecodeMessageCB message_cb;
 	LogicalDecodeFilterByOriginCB filter_by_origin_cb;
 	LogicalDecodeShutdownCB shutdown_cb;
 } OutputPluginCallbacks;
diff --git a/src/include/replication/reorderbuffer.h b/src/include/replication/reorderbuffer.h
index b52d06a..c12dbf4 100644
--- a/src/include/replication/reorderbuffer.h
+++ b/src/include/replication/reorderbuffer.h
@@ -54,6 +54,7 @@ enum ReorderBufferChangeType
 	REORDER_BUFFER_CHANGE_INSERT,
 	REORDER_BUFFER_CHANGE_UPDATE,
 	REORDER_BUFFER_CHANGE_DELETE,
+	REORDER_BUFFER_CHANGE_MESSAGE,
 	REORDER_BUFFER_CHANGE_INTERNAL_SNAPSHOT,
 	REORDER_BUFFER_CHANGE_INTERNAL_COMMAND_ID,
 	REORDER_BUFFER_CHANGE_INTERNAL_TUPLECID,
@@ -98,6 +99,14 @@ typedef struct ReorderBufferChange
 			ReorderBufferTupleBuf *newtuple;
 		}			tp;
 
+		/* Message with arbitrary data. */
+		struct
+		{
+			char *prefix;
+			size_t message_size;
+			char *message;
+		} msg;
+
 		/* New snapshot, set when action == *_INTERNAL_SNAPSHOT */
 		Snapshot	snapshot;
 
@@ -274,6 +283,14 @@ typedef void (*ReorderBufferCommitCB) (
 												   ReorderBufferTXN *txn,
 												   XLogRecPtr commit_lsn);
 
+/* message callback signature */
+typedef void (*ReorderBufferMessageCB) (
+												   ReorderBuffer *rb,
+												   ReorderBufferTXN *txn,
+												   XLogRecPtr message_lsn,
+												   const char *prefix, Size sz,
+												   const char *message);
+
 struct ReorderBuffer
 {
 	/*
@@ -300,6 +317,7 @@ struct ReorderBuffer
 	ReorderBufferBeginCB begin;
 	ReorderBufferApplyChangeCB apply_change;
 	ReorderBufferCommitCB commit;
+	ReorderBufferMessageCB message;
 
 	/*
 	 * Pointer that will be passed untouched to the callbacks.
@@ -350,6 +368,8 @@ ReorderBufferChange *ReorderBufferGetChange(ReorderBuffer *);
 void		ReorderBufferReturnChange(ReorderBuffer *, ReorderBufferChange *);
 
 void		ReorderBufferQueueChange(ReorderBuffer *, TransactionId, XLogRecPtr lsn, ReorderBufferChange *);
+void		ReorderBufferQueueMessage(ReorderBuffer *, TransactionId, XLogRecPtr lsn,
+									  const char *prefix, Size msg_sz, const char *msg);
 void ReorderBufferCommit(ReorderBuffer *, TransactionId,
 					XLogRecPtr commit_lsn, XLogRecPtr end_lsn,
 	  TimestampTz commit_time, RepOriginId origin_id, XLogRecPtr origin_lsn);
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index 75955af..c4127a1 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -63,6 +63,8 @@ extern const char *SnapBuildExportSnapshot(SnapBuild *snapstate);
 extern void SnapBuildClearExportedSnapshot(void);
 
 extern SnapBuildState SnapBuildCurrentState(SnapBuild *snapstate);
+extern Snapshot SnapBuildGetOrBuildSnapshot(SnapBuild *builder,
+											TransactionId xid);
 
 extern bool SnapBuildXactNeedsSkip(SnapBuild *snapstate, XLogRecPtr ptr);
 
-- 
1.9.1

From 77fce7aaf550186c853dd6c2eaba31458af13be5 Mon Sep 17 00:00:00 2001
From: Petr Jelinek <pjmodos@pjmodos.net>
Date: Wed, 24 Feb 2016 17:02:36 +0100
Subject: [PATCH] Logical Decoding Messages

---
 contrib/test_decoding/Makefile                  |  2 +-
 contrib/test_decoding/expected/ddl.out          | 21 ++++--
 contrib/test_decoding/expected/messages.out     | 56 +++++++++++++++
 contrib/test_decoding/sql/ddl.sql               |  3 +-
 contrib/test_decoding/sql/messages.sql          | 17 +++++
 contrib/test_decoding/test_decoding.c           | 17 +++++
 doc/src/sgml/func.sgml                          | 45 ++++++++++++
 doc/src/sgml/logicaldecoding.sgml               | 34 +++++++++
 src/backend/access/rmgrdesc/Makefile            |  4 +-
 src/backend/access/rmgrdesc/logicalmsgdesc.c    | 41 +++++++++++
 src/backend/access/transam/rmgr.c               |  1 +
 src/backend/replication/logical/Makefile        |  2 +-
 src/backend/replication/logical/decode.c        | 65 +++++++++++++++++
 src/backend/replication/logical/logical.c       | 37 ++++++++++
 src/backend/replication/logical/logicalfuncs.c  | 27 +++++++
 src/backend/replication/logical/message.c       | 85 ++++++++++++++++++++++
 src/backend/replication/logical/reorderbuffer.c | 93 +++++++++++++++++++++++++
 src/backend/replication/logical/snapbuild.c     | 19 +++++
 src/bin/pg_xlogdump/.gitignore                  | 20 +-----
 src/bin/pg_xlogdump/rmgrdesc.c                  |  1 +
 src/include/access/rmgrlist.h                   |  1 +
 src/include/catalog/pg_proc.h                   |  4 ++
 src/include/replication/logicalfuncs.h          |  2 +
 src/include/replication/message.h               | 41 +++++++++++
 src/include/replication/output_plugin.h         | 12 ++++
 src/include/replication/reorderbuffer.h         | 20 ++++++
 src/include/replication/snapbuild.h             |  2 +
 27 files changed, 641 insertions(+), 31 deletions(-)
 create mode 100644 contrib/test_decoding/expected/messages.out
 create mode 100644 contrib/test_decoding/sql/messages.sql
 create mode 100644 src/backend/access/rmgrdesc/logicalmsgdesc.c
 create mode 100644 src/backend/replication/logical/message.c
 create mode 100644 src/include/replication/message.h

diff --git a/contrib/test_decoding/Makefile b/contrib/test_decoding/Makefile
index 06c9546..309cb0b 100644
--- a/contrib/test_decoding/Makefile
+++ b/contrib/test_decoding/Makefile
@@ -38,7 +38,7 @@ submake-test_decoding:
 	$(MAKE) -C $(top_builddir)/contrib/test_decoding
 
 REGRESSCHECKS=ddl xact rewrite toast permissions decoding_in_xact \
-	decoding_into_rel binary prepared replorigin time
+	decoding_into_rel binary prepared replorigin time messages
 
 regresscheck: | submake-regress submake-test_decoding temp-install
 	$(MKDIR_P) regression_output
diff --git a/contrib/test_decoding/expected/ddl.out b/contrib/test_decoding/expected/ddl.out
index 77719e8..32cd24d 100644
--- a/contrib/test_decoding/expected/ddl.out
+++ b/contrib/test_decoding/expected/ddl.out
@@ -220,11 +220,17 @@ SELECT data FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'inc
 (7 rows)
 
 /*
- * check that disk spooling works
+ * check that disk spooling works (also for logical messages)
  */
 BEGIN;
 CREATE TABLE tr_etoomuch (id serial primary key, data int);
 INSERT INTO tr_etoomuch(data) SELECT g.i FROM generate_series(1, 10234) g(i);
+SELECT 'tx logical msg' FROM pg_logical_emit_message(true, 'test', 'tx logical msg');
+    ?column?    
+----------------
+ tx logical msg
+(1 row)
+
 DELETE FROM tr_etoomuch WHERE id < 5000;
 UPDATE tr_etoomuch SET data = - data WHERE id > 5000;
 COMMIT;
@@ -233,12 +239,13 @@ SELECT count(*), min(data), max(data)
 FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'include-xids', '0', 'skip-empty-xacts', '1')
 GROUP BY substring(data, 1, 24)
 ORDER BY 1,2;
- count |                       min                       |                                  max                                   
--------+-------------------------------------------------+------------------------------------------------------------------------
-     1 | BEGIN                                           | BEGIN
-     1 | COMMIT                                          | COMMIT
- 20467 | table public.tr_etoomuch: DELETE: id[integer]:1 | table public.tr_etoomuch: UPDATE: id[integer]:9999 data[integer]:-9999
-(3 rows)
+ count |                                  min                                  |                                  max                                   
+-------+-----------------------------------------------------------------------+------------------------------------------------------------------------
+     1 | BEGIN                                                                 | BEGIN
+     1 | COMMIT                                                                | COMMIT
+     1 | message: transactional: 1 prefix: test, sz: 14 content:tx logical msg | message: transactional: 1 prefix: test, sz: 14 content:tx logical msg
+ 20467 | table public.tr_etoomuch: DELETE: id[integer]:1                       | table public.tr_etoomuch: UPDATE: id[integer]:9999 data[integer]:-9999
+(4 rows)
 
 -- check updates of primary keys work correctly
 BEGIN;
diff --git a/contrib/test_decoding/expected/messages.out b/contrib/test_decoding/expected/messages.out
new file mode 100644
index 0000000..7fa8256
--- /dev/null
+++ b/contrib/test_decoding/expected/messages.out
@@ -0,0 +1,56 @@
+-- predictability
+SET synchronous_commit = on;
+SELECT 'init' FROM pg_create_logical_replication_slot('regression_slot', 'test_decoding');
+ ?column? 
+----------
+ init
+(1 row)
+
+SELECT 'msg1' FROM pg_logical_emit_message(true, 'test', 'msg1');
+ ?column? 
+----------
+ msg1
+(1 row)
+
+SELECT 'msg2' FROM pg_logical_emit_message(false, 'test', 'msg2');
+ ?column? 
+----------
+ msg2
+(1 row)
+
+BEGIN;
+SELECT 'msg3' FROM pg_logical_emit_message(true, 'test', 'msg3');
+ ?column? 
+----------
+ msg3
+(1 row)
+
+SELECT 'msg4' FROM pg_logical_emit_message(false, 'test', 'msg4');
+ ?column? 
+----------
+ msg4
+(1 row)
+
+SELECT 'msg5' FROM pg_logical_emit_message(true, 'test', 'msg5');
+ ?column? 
+----------
+ msg5
+(1 row)
+
+COMMIT;
+SELECT data FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'force-binary', '0', 'skip-empty-xacts', '1');
+                            data                            
+------------------------------------------------------------
+ message: transactional: 1 prefix: test, sz: 4 content:msg1
+ message: transactional: 0 prefix: test, sz: 4 content:msg2
+ message: transactional: 0 prefix: test, sz: 4 content:msg4
+ message: transactional: 1 prefix: test, sz: 4 content:msg3
+ message: transactional: 1 prefix: test, sz: 4 content:msg5
+(5 rows)
+
+SELECT 'init' FROM pg_drop_replication_slot('regression_slot');
+ ?column? 
+----------
+ init
+(1 row)
+
diff --git a/contrib/test_decoding/sql/ddl.sql b/contrib/test_decoding/sql/ddl.sql
index ad928ad..b1f7bf6 100644
--- a/contrib/test_decoding/sql/ddl.sql
+++ b/contrib/test_decoding/sql/ddl.sql
@@ -108,11 +108,12 @@ DELETE FROM tr_pkey;
 SELECT data FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'include-xids', '0', 'skip-empty-xacts', '1');
 
 /*
- * check that disk spooling works
+ * check that disk spooling works (also for logical messages)
  */
 BEGIN;
 CREATE TABLE tr_etoomuch (id serial primary key, data int);
 INSERT INTO tr_etoomuch(data) SELECT g.i FROM generate_series(1, 10234) g(i);
+SELECT 'tx logical msg' FROM pg_logical_emit_message(true, 'test', 'tx logical msg');
 DELETE FROM tr_etoomuch WHERE id < 5000;
 UPDATE tr_etoomuch SET data = - data WHERE id > 5000;
 COMMIT;
diff --git a/contrib/test_decoding/sql/messages.sql b/contrib/test_decoding/sql/messages.sql
new file mode 100644
index 0000000..8744eb6
--- /dev/null
+++ b/contrib/test_decoding/sql/messages.sql
@@ -0,0 +1,17 @@
+-- predictability
+SET synchronous_commit = on;
+
+SELECT 'init' FROM pg_create_logical_replication_slot('regression_slot', 'test_decoding');
+
+SELECT 'msg1' FROM pg_logical_emit_message(true, 'test', 'msg1');
+SELECT 'msg2' FROM pg_logical_emit_message(false, 'test', 'msg2');
+
+BEGIN;
+SELECT 'msg3' FROM pg_logical_emit_message(true, 'test', 'msg3');
+SELECT 'msg4' FROM pg_logical_emit_message(false, 'test', 'msg4');
+SELECT 'msg5' FROM pg_logical_emit_message(true, 'test', 'msg5');
+COMMIT;
+
+SELECT data FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'force-binary', '0', 'skip-empty-xacts', '1');
+
+SELECT 'init' FROM pg_drop_replication_slot('regression_slot');
diff --git a/contrib/test_decoding/test_decoding.c b/contrib/test_decoding/test_decoding.c
index 4cf808f..1997774 100644
--- a/contrib/test_decoding/test_decoding.c
+++ b/contrib/test_decoding/test_decoding.c
@@ -21,6 +21,7 @@
 
 #include "replication/output_plugin.h"
 #include "replication/logical.h"
+#include "replication/message.h"
 #include "replication/origin.h"
 
 #include "utils/builtins.h"
@@ -63,6 +64,9 @@ static void pg_decode_change(LogicalDecodingContext *ctx,
 				 ReorderBufferChange *change);
 static bool pg_decode_filter(LogicalDecodingContext *ctx,
 				 RepOriginId origin_id);
+static void pg_decode_message(LogicalDecodingContext *ctx,
+							  ReorderBufferTXN *txn, XLogRecPtr message_lsn,
+							  const char *prefix, Size sz, const char *message);
 
 void
 _PG_init(void)
@@ -82,6 +86,7 @@ _PG_output_plugin_init(OutputPluginCallbacks *cb)
 	cb->commit_cb = pg_decode_commit_txn;
 	cb->filter_by_origin_cb = pg_decode_filter;
 	cb->shutdown_cb = pg_decode_shutdown;
+	cb->message_cb = pg_decode_message;
 }
 
 
@@ -471,3 +476,15 @@ pg_decode_change(LogicalDecodingContext *ctx, ReorderBufferTXN *txn,
 
 	OutputPluginWrite(ctx, true);
 }
+
+static void
+pg_decode_message(LogicalDecodingContext *ctx,
+				  ReorderBufferTXN *txn, XLogRecPtr lsn,
+				  const char *prefix, Size sz, const char *message)
+{
+	OutputPluginPrepareWrite(ctx, true);
+	appendStringInfo(ctx->out, "message: transactional: %d prefix: %s, sz: %zu content:",
+					 txn != NULL, prefix, sz);
+	appendBinaryStringInfo(ctx->out, message, sz);
+	OutputPluginWrite(ctx, true);
+}
diff --git a/doc/src/sgml/func.sgml b/doc/src/sgml/func.sgml
index ae93e69..7ac71d1 100644
--- a/doc/src/sgml/func.sgml
+++ b/doc/src/sgml/func.sgml
@@ -18238,6 +18238,51 @@ postgres=# SELECT * FROM pg_xlogfile_name_offset(pg_stop_backup());
        </entry>
       </row>
 
+      <row>
+       <entry id="pg-logical-emit-message-text">
+        <indexterm>
+         <primary>pg_logical_emit_message</primary>
+        </indexterm>
+        <literal><function>pg_logical_emit_message(<parameter>transactional</parameter> <type>bool</type>, <parameter>prefix</parameter> <type>text</type>, <parameter>content</parameter> <type>text</type>)</function></literal>
+       </entry>
+       <entry>
+        void
+       </entry>
+       <entry>
+        Emit text logical decoding message. This can be used to pass generic
+        messages to logical decoding plugins through WAL. The parameter
+        <parameter>transactional</parameter> specifies if the message should
+        be part of current transaction or if it should be written immediately
+        and decoded as soon as the logical decoding reads the record. The
+        <parameter>prefix</parameter> is textual prefix used by the logical
+        decoding plugins to easily recognize interesting messages for them.
+        The <parameter>content</parameter> is the text of the message.
+       </entry>
+      </row>
+
+      <row>
+       <entry id="pg-logical-emit-message-bytea">
+        <indexterm>
+         <primary>>pg_logical_emit_message</primary>
+        </indexterm>
+        <literal><function>>pg_logical_emit_message(<parameter>transactional</parameter> <type>bool</type>, <parameter>prefix</parameter> <type>text</type>, <parameter>content</parameter> <type>bytea</type>)</function></literal>
+       </entry>
+       <entry>
+        void
+       </entry>
+       <entry>
+        Emit binary logical decoding message. This can be used to pass generic
+        messages to logical decoding plugins through WAL. The parameter
+        <parameter>transactional</parameter> specifies if the message should
+        be part of current transaction or if it should be written immediately
+        and decoded as soon as the logical decoding reads the record. The
+        <parameter>prefix</parameter> is textual prefix used by the logical
+        decoding plugins to easily recognize interesting messages for them.
+        The <parameter>content</parameter> is the binary content of the
+        message.
+       </entry>
+      </row>
+
      </tbody>
     </tgroup>
    </table>
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 45fdfeb..7c9d03a 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -363,6 +363,7 @@ typedef struct OutputPluginCallbacks
     LogicalDecodeBeginCB begin_cb;
     LogicalDecodeChangeCB change_cb;
     LogicalDecodeCommitCB commit_cb;
+    LogicalDecodeMessageCB message_cb;
     LogicalDecodeFilterByOriginCB filter_by_origin_cb;
     LogicalDecodeShutdownCB shutdown_cb;
 } OutputPluginCallbacks;
@@ -602,6 +603,39 @@ typedef bool (*LogicalDecodeFilterByOriginCB) (
        more efficient.
      </para>
      </sect3>
+
+    <sect3 id="logicaldecoding-output-plugin-message">
+     <title>Generic Message Callback</title>
+
+     <para>
+      The optional <function>message_cb</function> callback is called whenever
+      a logical decoding message has been decoded.
+<programlisting>
+typedef void (*LogicalDecodeMessageCB) (
+    struct LogicalDecodingContext *,
+    ReorderBufferTXN *txn,
+    XLogRecPtr message_lsn,
+    const char *prefix,
+    Size message_size,
+    const char *message
+);
+</programlisting>
+      The <parameter>ctx</parameter> and <parameter>txn</parameter> parameters
+      have the same contents as for the <function>begin_cb</function> with the
+      difference that <parameter>txn</parameter> is null for non-transactional
+      messages. The <parameter>lsn</parameter> has WAL position of the message.
+      The <parameter>prefix</parameter> is arbitrary textual prefix which can
+      be used for identifying interesting messages for the current plugin.
+      And finally the <parameter>message</parameter> parameter holds the
+      actual message of <parameter>message_size</parameter> size.
+     </para>
+     <para>
+      Extra care should be taken to ensure that the prefix the output plugin
+      considers interesting is unique. Using name of the extension or the
+      output plugin itself is often a good choice.
+     </para>
+    </sect3>
+
    </sect2>
 
    <sect2 id="logicaldecoding-output-plugin-output">
diff --git a/src/backend/access/rmgrdesc/Makefile b/src/backend/access/rmgrdesc/Makefile
index c72a1f2..723b4d8 100644
--- a/src/backend/access/rmgrdesc/Makefile
+++ b/src/backend/access/rmgrdesc/Makefile
@@ -9,8 +9,8 @@ top_builddir = ../../../..
 include $(top_builddir)/src/Makefile.global
 
 OBJS = brindesc.o clogdesc.o committsdesc.o dbasedesc.o gindesc.o gistdesc.o \
-	   hashdesc.o heapdesc.o mxactdesc.o nbtdesc.o relmapdesc.o \
-	   replorigindesc.o seqdesc.o smgrdesc.o spgdesc.o \
+	   hashdesc.o heapdesc.o logicalmsgdesc.o mxactdesc.o nbtdesc.o \
+	   relmapdesc.o replorigindesc.o seqdesc.o smgrdesc.o spgdesc.o \
 	   standbydesc.o tblspcdesc.o xactdesc.o xlogdesc.o
 
 include $(top_srcdir)/src/backend/common.mk
diff --git a/src/backend/access/rmgrdesc/logicalmsgdesc.c b/src/backend/access/rmgrdesc/logicalmsgdesc.c
new file mode 100644
index 0000000..b194e14
--- /dev/null
+++ b/src/backend/access/rmgrdesc/logicalmsgdesc.c
@@ -0,0 +1,41 @@
+/*-------------------------------------------------------------------------
+ *
+ * logicalmsgdesc.c
+ *	  rmgr descriptor routines for replication/logical/message.c
+ *
+ * Portions Copyright (c) 2015-2016, PostgreSQL Global Development Group
+ *
+ *
+ * IDENTIFICATION
+ *	  src/backend/access/rmgrdesc/logicalmsgdesc.c
+ *
+ *-------------------------------------------------------------------------
+ */
+#include "postgres.h"
+
+#include "replication/message.h"
+
+void
+logicalmsg_desc(StringInfo buf, XLogReaderState *record)
+{
+	char	   *rec = XLogRecGetData(record);
+	uint8		info = XLogRecGetInfo(record) & ~XLR_INFO_MASK;
+
+	if (info == XLOG_LOGICAL_MESSAGE)
+	{
+		xl_logical_message *xlrec = (xl_logical_message *) rec;
+
+		appendStringInfo(buf, "%s message size %zu bytes",
+				   xlrec->transactional ? "transactional" : "nontransactional",
+						 xlrec->message_size);
+	}
+}
+
+const char *
+logicalmsg_identify(uint8 info)
+{
+	if ((info & ~XLR_INFO_MASK) == XLOG_LOGICAL_MESSAGE)
+		return "MESSAGE";
+
+	return NULL;
+}
diff --git a/src/backend/access/transam/rmgr.c b/src/backend/access/transam/rmgr.c
index 7c4d773..1a42121 100644
--- a/src/backend/access/transam/rmgr.c
+++ b/src/backend/access/transam/rmgr.c
@@ -23,6 +23,7 @@
 #include "commands/dbcommands_xlog.h"
 #include "commands/sequence.h"
 #include "commands/tablespace.h"
+#include "replication/message.h"
 #include "replication/origin.h"
 #include "storage/standby.h"
 #include "utils/relmapper.h"
diff --git a/src/backend/replication/logical/Makefile b/src/backend/replication/logical/Makefile
index 8adea13..1d7ca06 100644
--- a/src/backend/replication/logical/Makefile
+++ b/src/backend/replication/logical/Makefile
@@ -14,7 +14,7 @@ include $(top_builddir)/src/Makefile.global
 
 override CPPFLAGS := -I$(srcdir) $(CPPFLAGS)
 
-OBJS = decode.o logical.o logicalfuncs.o reorderbuffer.o origin.o \
+OBJS = decode.o logical.o logicalfuncs.o message.o origin.o reorderbuffer.o \
 	snapbuild.o
 
 include $(top_srcdir)/src/backend/common.mk
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index 13af485..30ccf07 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -39,6 +39,7 @@
 
 #include "replication/decode.h"
 #include "replication/logical.h"
+#include "replication/message.h"
 #include "replication/reorderbuffer.h"
 #include "replication/origin.h"
 #include "replication/snapbuild.h"
@@ -58,6 +59,7 @@ static void DecodeHeapOp(LogicalDecodingContext *ctx, XLogRecordBuffer *buf);
 static void DecodeHeap2Op(LogicalDecodingContext *ctx, XLogRecordBuffer *buf);
 static void DecodeXactOp(LogicalDecodingContext *ctx, XLogRecordBuffer *buf);
 static void DecodeStandbyOp(LogicalDecodingContext *ctx, XLogRecordBuffer *buf);
+static void DecodeLogicalMsgOp(LogicalDecodingContext *ctx, XLogRecordBuffer *buf);
 
 /* individual record(group)'s handlers */
 static void DecodeInsert(LogicalDecodingContext *ctx, XLogRecordBuffer *buf);
@@ -123,6 +125,10 @@ LogicalDecodingProcessRecord(LogicalDecodingContext *ctx, XLogReaderState *recor
 			DecodeHeapOp(ctx, &buf);
 			break;
 
+		case RM_LOGICALMSG_ID:
+			DecodeLogicalMsgOp(ctx, &buf);
+			break;
+
 			/*
 			 * Rmgrs irrelevant for logical decoding; they describe stuff not
 			 * represented in logical decoding. Add new rmgrs in rmgrlist.h's
@@ -457,6 +463,65 @@ DecodeHeapOp(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
 	}
 }
 
+/*
+ * Handle rmgr LOGICALMSG_ID records for DecodeRecordIntoReorderBuffer().
+ */
+static void
+DecodeLogicalMsgOp(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
+{
+	SnapBuild  *builder = ctx->snapshot_builder;
+	XLogReaderState *r = buf->record;
+	uint8		info = XLogRecGetInfo(r) & ~XLR_INFO_MASK;
+	xl_logical_message *message;
+
+	if (info != XLOG_LOGICAL_MESSAGE)
+		elog(ERROR, "unexpected RM_LOGICALMSG_ID record type: %u", info);
+
+	ReorderBufferProcessXid(ctx->reorder, XLogRecGetXid(r), buf->origptr);
+
+	message = (xl_logical_message *) XLogRecGetData(r);
+
+	/*
+	 * Transactional messages goe to RecordBuffer, while non-transactional
+	 * ones get sent to output plugin immediately.
+	 */
+	if (message->transactional)
+	{
+		if (!SnapBuildProcessChange(builder, XLogRecGetXid(r), buf->origptr))
+			return;
+
+		ReorderBufferQueueMessage(ctx->reorder, XLogRecGetXid(r),
+								  buf->endptr,
+								  message->message, /* first part of message is prefix */
+								  message->message_size,
+								  message->message + message->prefix_size);
+	}
+	else if (SnapBuildCurrentState(builder) == SNAPBUILD_CONSISTENT &&
+			 !SnapBuildXactNeedsSkip(builder, buf->origptr))
+	{
+		volatile Snapshot	snapshot_now;
+		ReorderBuffer	   *rb = ctx->reorder;
+
+		/* setup snapshot to allow catalog access */
+		snapshot_now = SnapBuildGetOrBuildSnapshot(builder, XLogRecGetXid(r));
+		SetupHistoricSnapshot(snapshot_now, NULL);
+		PG_TRY();
+		{
+			rb->message(rb, NULL, buf->origptr, message->message,
+						message->message_size,
+						message->message + message->prefix_size);
+
+			TeardownHistoricSnapshot(false);
+		}
+		PG_CATCH();
+		{
+			TeardownHistoricSnapshot(true);
+			PG_RE_THROW();
+		}
+		PG_END_TRY();
+	}
+}
+
 static inline bool
 FilterByOrigin(LogicalDecodingContext *ctx, RepOriginId origin_id)
 {
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index 2e6d3f9..7863d52 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -62,6 +62,9 @@ static void commit_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
 				  XLogRecPtr commit_lsn);
 static void change_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
 				  Relation relation, ReorderBufferChange *change);
+static void message_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
+				  XLogRecPtr message_lsn, const char *prefix, Size sz,
+				  const char *message);
 
 static void LoadOutputPlugin(OutputPluginCallbacks *callbacks, char *plugin);
 
@@ -178,6 +181,7 @@ StartupDecodingContext(List *output_plugin_options,
 	ctx->reorder->begin = begin_cb_wrapper;
 	ctx->reorder->apply_change = change_cb_wrapper;
 	ctx->reorder->commit = commit_cb_wrapper;
+	ctx->reorder->message = message_cb_wrapper;
 
 	ctx->out = makeStringInfo();
 	ctx->prepare_write = prepare_write;
@@ -702,6 +706,39 @@ filter_by_origin_cb_wrapper(LogicalDecodingContext *ctx, RepOriginId origin_id)
 	return ret;
 }
 
+static void
+message_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
+				   XLogRecPtr message_lsn, const char *prefix, Size sz,
+				   const char *message)
+{
+	LogicalDecodingContext *ctx = cache->private_data;
+	LogicalErrorCallbackState state;
+	ErrorContextCallback errcallback;
+
+	if (ctx->callbacks.message_cb == NULL)
+		return;
+
+	/* Push callback + info on the error context stack */
+	state.ctx = ctx;
+	state.callback_name = "message";
+	state.report_location = message_lsn;
+	errcallback.callback = output_plugin_error_callback;
+	errcallback.arg = (void *) &state;
+	errcallback.previous = error_context_stack;
+	error_context_stack = &errcallback;
+
+	/* set output state */
+	ctx->accept_writes = true;
+	ctx->write_xid = txn != NULL ? txn->xid : InvalidTransactionId;
+	ctx->write_location = message_lsn;
+
+	/* do the actual work: call callback */
+	ctx->callbacks.message_cb(ctx, txn, message_lsn, prefix, sz, message);
+
+	/* Pop the error context stack */
+	error_context_stack = errcallback.previous;
+}
+
 /*
  * Set the required catalog xmin horizon for historic snapshots in the current
  * replication slot.
diff --git a/src/backend/replication/logical/logicalfuncs.c b/src/backend/replication/logical/logicalfuncs.c
index f789fc1..552dac3 100644
--- a/src/backend/replication/logical/logicalfuncs.c
+++ b/src/backend/replication/logical/logicalfuncs.c
@@ -24,6 +24,8 @@
 #include "access/xlog_internal.h"
 #include "access/xlogutils.h"
 
+#include "access/xact.h"
+
 #include "catalog/pg_type.h"
 
 #include "nodes/makefuncs.h"
@@ -41,6 +43,7 @@
 #include "replication/decode.h"
 #include "replication/logical.h"
 #include "replication/logicalfuncs.h"
+#include "replication/message.h"
 
 #include "storage/fd.h"
 
@@ -363,3 +366,27 @@ pg_logical_slot_peek_binary_changes(PG_FUNCTION_ARGS)
 {
 	return pg_logical_slot_get_changes_guts(fcinfo, false, true);
 }
+
+
+/*
+ * SQL function for writing logical decding message into WAL.
+ */
+Datum
+pg_logical_emit_message_bytea(PG_FUNCTION_ARGS)
+{
+	bool		transactional = PG_GETARG_BOOL(0);
+	char	   *prefix = text_to_cstring(PG_GETARG_TEXT_PP(1));
+	bytea	   *data = PG_GETARG_BYTEA_PP(2);
+	XLogRecPtr	lsn;
+
+	lsn = LogLogicalMessage(prefix, VARDATA_ANY(data), VARSIZE_ANY_EXHDR(data),
+							transactional);
+	PG_RETURN_LSN(lsn);
+}
+
+Datum
+pg_logical_emit_message_text(PG_FUNCTION_ARGS)
+{
+	/* bytea and text are compatible */
+	return pg_logical_emit_message_bytea(fcinfo);
+}
diff --git a/src/backend/replication/logical/message.c b/src/backend/replication/logical/message.c
new file mode 100644
index 0000000..85c597b
--- /dev/null
+++ b/src/backend/replication/logical/message.c
@@ -0,0 +1,85 @@
+/*-------------------------------------------------------------------------
+ *
+ * message.c
+ *	  Generic logical messages.
+ *
+ * Copyright (c) 2013-2016, PostgreSQL Global Development Group
+ *
+ * IDENTIFICATION
+ *	  src/backend/replication/logical/message.c
+ *
+ * NOTES
+ *
+ * Generic logical messages allow XLOG logging of arbitrary binary blobs that
+ * get passed to the logical decoding plugin. In normal XLOG processing they
+ * are same as NOOP.
+ *
+ * These messages can be either transactional or non-transactional.
+ * Transactional messages are part of current transaction and will be sent to
+ * decoding plugin using in a same way as DML operations.
+ * Non-transactional messages are sent to the plugin at the time when the
+ * logical decoding reads them from XLOG.
+ *
+ * Every message carries prefix to avoid conflicts between different decoding
+ * plugins. The plugin authors must take extra care to use unique prefix,
+ * good options seems to be for example to use the name of the extension.
+ *
+ * ---------------------------------------------------------------------------
+ */
+
+#include "postgres.h"
+
+#include "access/xact.h"
+
+#include "catalog/indexing.h"
+
+#include "nodes/execnodes.h"
+
+#include "replication/message.h"
+#include "replication/logical.h"
+
+#include "utils/memutils.h"
+
+/*
+ * Write logical decoding message into XLog.
+ */
+XLogRecPtr
+LogLogicalMessage(const char *prefix, const char *message, size_t size,
+				  bool transactional)
+{
+	xl_logical_message	xlrec;
+
+	/*
+	 * Force xid to be allocated if we're emitting a transactional message.
+	 */
+	if (transactional)
+	{
+		Assert(IsTransactionState());
+		GetCurrentTransactionId();
+	}
+
+	xlrec.transactional = transactional;
+	xlrec.prefix_size = strlen(prefix) + 1;
+	xlrec.message_size = size;
+
+	XLogBeginInsert();
+	XLogRegisterData((char *) &xlrec, SizeOfLogicalMessage);
+	XLogRegisterData((char *) prefix, xlrec.prefix_size);
+	XLogRegisterData((char *) message, size);
+
+	return XLogInsert(RM_LOGICALMSG_ID, XLOG_LOGICAL_MESSAGE);
+}
+
+/*
+ * Redo is basically just noop for logical decoding messages.
+ */
+void
+logicalmsg_redo(XLogReaderState *record)
+{
+	uint8		info = XLogRecGetInfo(record) & ~XLR_INFO_MASK;
+
+	if (info != XLOG_LOGICAL_MESSAGE)
+			elog(PANIC, "logicalmsg_redo: unknown op code %u", info);
+
+	/* This is only interesting for logical decoding, see decode.c. */
+}
diff --git a/src/backend/replication/logical/reorderbuffer.c b/src/backend/replication/logical/reorderbuffer.c
index f2b8f4b..7894971 100644
--- a/src/backend/replication/logical/reorderbuffer.c
+++ b/src/backend/replication/logical/reorderbuffer.c
@@ -414,6 +414,14 @@ ReorderBufferReturnChange(ReorderBuffer *rb, ReorderBufferChange *change)
 				change->data.tp.oldtuple = NULL;
 			}
 			break;
+		case REORDER_BUFFER_CHANGE_MESSAGE:
+			if (change->data.msg.prefix != NULL)
+				pfree(change->data.msg.prefix);
+			change->data.msg.prefix = NULL;
+			if (change->data.msg.message != NULL)
+				pfree(change->data.msg.message);
+			change->data.msg.message = NULL;
+			break;
 		case REORDER_BUFFER_CHANGE_INTERNAL_SNAPSHOT:
 			if (change->data.snapshot)
 			{
@@ -627,6 +635,33 @@ ReorderBufferQueueChange(ReorderBuffer *rb, TransactionId xid, XLogRecPtr lsn,
 	ReorderBufferCheckSerializeTXN(rb, txn);
 }
 
+/*
+ * Queue message into a transaction so it can be processed upon commit.
+ */
+void
+ReorderBufferQueueMessage(ReorderBuffer *rb, TransactionId xid, XLogRecPtr lsn,
+						  const char *prefix, Size msg_sz, const char *msg)
+{
+	MemoryContext oldcontext;
+	ReorderBufferChange *change;
+
+	Assert(xid != InvalidTransactionId);
+
+	oldcontext = MemoryContextSwitchTo(rb->context);
+
+	change = ReorderBufferGetChange(rb);
+	change->action = REORDER_BUFFER_CHANGE_MESSAGE;
+	change->data.msg.prefix = pstrdup(prefix);
+	change->data.msg.message_size = msg_sz;
+	change->data.msg.message = palloc(msg_sz);
+	memcpy(change->data.msg.message, msg, msg_sz);
+
+	ReorderBufferQueueChange(rb, xid, lsn, change);
+
+	MemoryContextSwitchTo(oldcontext);
+}
+
+
 static void
 AssertTXNLsnOrder(ReorderBuffer *rb)
 {
@@ -1493,6 +1528,13 @@ ReorderBufferCommit(ReorderBuffer *rb, TransactionId xid,
 					specinsert = change;
 					break;
 
+				case REORDER_BUFFER_CHANGE_MESSAGE:
+					rb->message(rb, txn, change->lsn,
+								change->data.msg.prefix,
+								change->data.msg.message_size,
+								change->data.msg.message);
+					break;
+
 				case REORDER_BUFFER_CHANGE_INTERNAL_SNAPSHOT:
 					/* get rid of the old */
 					TeardownHistoricSnapshot(false);
@@ -2159,6 +2201,33 @@ ReorderBufferSerializeChange(ReorderBuffer *rb, ReorderBufferTXN *txn,
 				}
 				break;
 			}
+		case REORDER_BUFFER_CHANGE_MESSAGE:
+			{
+				char	   *data;
+				Size		prefix_size = strlen(change->data.msg.prefix) + 1;
+
+				sz += prefix_size + change->data.msg.message_size +
+					sizeof(Size) + sizeof(Size);
+				ReorderBufferSerializeReserve(rb, sz);
+
+				data = ((char *) rb->outbuf) + sizeof(ReorderBufferDiskChange);
+
+				/* write the prefix including the size */
+				memcpy(data, &prefix_size, sizeof(Size));
+				data += sizeof(Size);
+				memcpy(data, change->data.msg.prefix,
+					   prefix_size);
+				data += prefix_size;
+
+				/* write the message including the size */
+				memcpy(data, &change->data.msg.message_size, sizeof(Size));
+				data += sizeof(Size);
+				memcpy(data, change->data.msg.message,
+					   change->data.msg.message_size);
+				data += change->data.msg.message_size;
+
+				break;
+			}
 		case REORDER_BUFFER_CHANGE_INTERNAL_SNAPSHOT:
 			{
 				Snapshot	snap;
@@ -2415,6 +2484,30 @@ ReorderBufferRestoreChange(ReorderBuffer *rb, ReorderBufferTXN *txn,
 			}
 
 			break;
+		case REORDER_BUFFER_CHANGE_MESSAGE:
+			{
+				Size		prefix_size;
+
+				/* read prefix */
+				memcpy(&prefix_size, data, sizeof(Size));
+				data += sizeof(Size);
+				change->data.msg.prefix = MemoryContextAlloc(rb->context,
+															 prefix_size);
+				memcpy(change->data.msg.prefix, data, prefix_size);
+				Assert(change->data.msg.prefix[prefix_size-1] == '\0');
+				data += prefix_size;
+
+				/* read the messsage */
+				memcpy(&change->data.msg.message_size, data, sizeof(Size));
+				data += sizeof(Size);
+				change->data.msg.message = MemoryContextAlloc(rb->context,
+												change->data.msg.message_size);
+				memcpy(change->data.msg.message, data,
+					   change->data.msg.message_size);
+				data += change->data.msg.message_size;
+
+				break;
+			}
 		case REORDER_BUFFER_CHANGE_INTERNAL_SNAPSHOT:
 			{
 				Snapshot	oldsnap;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index 179b85a..b4dc617 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -605,6 +605,25 @@ SnapBuildExportSnapshot(SnapBuild *builder)
 }
 
 /*
+ * Ensure there is a snapshot and if not build one for current transaction.
+ */
+Snapshot
+SnapBuildGetOrBuildSnapshot(SnapBuild *builder, TransactionId xid)
+{
+	Assert(builder->state == SNAPBUILD_CONSISTENT);
+
+	/* only build a new snapshot if we don't have a prebuilt one */
+	if (builder->snapshot == NULL)
+	{
+		builder->snapshot = SnapBuildBuildSnapshot(builder, xid);
+		/* inrease refcount for the snapshot builder */
+		SnapBuildSnapIncRefcount(builder->snapshot);
+	}
+
+	return builder->snapshot;
+}
+
+/*
  * Reset a previously SnapBuildExportSnapshot()'ed snapshot if there is
  * any. Aborts the previously started transaction and resets the resource
  * owner back to its original value.
diff --git a/src/bin/pg_xlogdump/.gitignore b/src/bin/pg_xlogdump/.gitignore
index eebaf30..c4783f1 100644
--- a/src/bin/pg_xlogdump/.gitignore
+++ b/src/bin/pg_xlogdump/.gitignore
@@ -1,22 +1,4 @@
 /pg_xlogdump
 # Source files copied from src/backend/access/rmgrdesc/
-/brindesc.c
-/clogdesc.c
-/committsdesc.c
-/dbasedesc.c
-/gindesc.c
-/gistdesc.c
-/hashdesc.c
-/heapdesc.c
-/mxactdesc.c
-/nbtdesc.c
-/relmapdesc.c
-/replorigindesc.c
-/seqdesc.c
-/smgrdesc.c
-/spgdesc.c
-/standbydesc.c
-/tblspcdesc.c
-/xactdesc.c
-/xlogdesc.c
+/*desc.c
 /xlogreader.c
diff --git a/src/bin/pg_xlogdump/rmgrdesc.c b/src/bin/pg_xlogdump/rmgrdesc.c
index f9cd395..6ba7f22 100644
--- a/src/bin/pg_xlogdump/rmgrdesc.c
+++ b/src/bin/pg_xlogdump/rmgrdesc.c
@@ -25,6 +25,7 @@
 #include "commands/dbcommands_xlog.h"
 #include "commands/sequence.h"
 #include "commands/tablespace.h"
+#include "replication/message.h"
 #include "replication/origin.h"
 #include "rmgrdesc.h"
 #include "storage/standbydefs.h"
diff --git a/src/include/access/rmgrlist.h b/src/include/access/rmgrlist.h
index fab912d..35c242d 100644
--- a/src/include/access/rmgrlist.h
+++ b/src/include/access/rmgrlist.h
@@ -45,3 +45,4 @@ PG_RMGR(RM_SPGIST_ID, "SPGist", spg_redo, spg_desc, spg_identify, spg_xlog_start
 PG_RMGR(RM_BRIN_ID, "BRIN", brin_redo, brin_desc, brin_identify, NULL, NULL)
 PG_RMGR(RM_COMMIT_TS_ID, "CommitTs", commit_ts_redo, commit_ts_desc, commit_ts_identify, NULL, NULL)
 PG_RMGR(RM_REPLORIGIN_ID, "ReplicationOrigin", replorigin_redo, replorigin_desc, replorigin_identify, NULL, NULL)
+PG_RMGR(RM_LOGICALMSG_ID, "LogicalMessage", logicalmsg_redo, logicalmsg_desc, logicalmsg_identify, NULL, NULL)
diff --git a/src/include/catalog/pg_proc.h b/src/include/catalog/pg_proc.h
index a595327..3713739 100644
--- a/src/include/catalog/pg_proc.h
+++ b/src/include/catalog/pg_proc.h
@@ -5114,6 +5114,10 @@ DATA(insert OID = 3784 (  pg_logical_slot_peek_changes PGNSP PGUID 12 1000 1000
 DESCR("peek at changes from replication slot");
 DATA(insert OID = 3785 (  pg_logical_slot_peek_binary_changes PGNSP PGUID 12 1000 1000 25 0 f f f f f t v u 4 0 2249 "19 3220 23 1009" "{19,3220,23,1009,3220,28,17}" "{i,i,i,v,o,o,o}" "{slot_name,upto_lsn,upto_nchanges,options,location,xid,data}" _null_ _null_ pg_logical_slot_peek_binary_changes _null_ _null_ _null_ ));
 DESCR("peek at binary changes from replication slot");
+DATA(insert OID = 3577 (  pg_logical_emit_message PGNSP PGUID 12 1 0 0 0 f f f f t f v u 3 0 3220 "16 25 25" _null_ _null_ _null_ _null_ _null_ pg_logical_emit_message_text _null_ _null_ _null_ ));
+DESCR("emit a textual logical decoding message");
+DATA(insert OID = 3578 (  pg_logical_emit_message PGNSP PGUID 12 1 0 0 0 f f f f t f v u 3 0 3220 "16 25 17" _null_ _null_ _null_ _null_ _null_ pg_logical_emit_message_bytea _null_ _null_ _null_ ));
+DESCR("emit a binary logical decoding message");
 
 /* event triggers */
 DATA(insert OID = 3566 (  pg_event_trigger_dropped_objects		PGNSP PGUID 12 10 100 0 0 f f f f t t s s 0 0 2249 "" "{26,26,23,16,16,16,25,25,25,25,1009,1009}" "{o,o,o,o,o,o,o,o,o,o,o,o}" "{classid, objid, objsubid, original, normal, is_temporary, object_type, schema_name, object_name, object_identity, address_names, address_args}" _null_ _null_ pg_event_trigger_dropped_objects _null_ _null_ _null_ ));
diff --git a/src/include/replication/logicalfuncs.h b/src/include/replication/logicalfuncs.h
index c87a1df..5540414 100644
--- a/src/include/replication/logicalfuncs.h
+++ b/src/include/replication/logicalfuncs.h
@@ -21,4 +21,6 @@ extern Datum pg_logical_slot_get_binary_changes(PG_FUNCTION_ARGS);
 extern Datum pg_logical_slot_peek_changes(PG_FUNCTION_ARGS);
 extern Datum pg_logical_slot_peek_binary_changes(PG_FUNCTION_ARGS);
 
+extern Datum pg_logical_emit_message_bytea(PG_FUNCTION_ARGS);
+extern Datum pg_logical_emit_message_text(PG_FUNCTION_ARGS);
 #endif
diff --git a/src/include/replication/message.h b/src/include/replication/message.h
new file mode 100644
index 0000000..b5c1ebf
--- /dev/null
+++ b/src/include/replication/message.h
@@ -0,0 +1,41 @@
+/*-------------------------------------------------------------------------
+ * message.h
+ *	   Exports from replication/logical/message.c
+ *
+ * Copyright (c) 2013-2016, PostgreSQL Global Development Group
+ *
+ * src/include/replication/message.h
+ *-------------------------------------------------------------------------
+ */
+#ifndef PG_LOGICAL_MESSAGE_H
+#define PG_LOGICAL_MESSAGE_H
+
+#include "access/xlog.h"
+#include "access/xlogdefs.h"
+#include "access/xlogreader.h"
+
+/*
+ * Generic logical decoding message wal record.
+ */
+typedef struct xl_logical_message
+{
+	bool		transactional;					/* is message transactional? */
+	size_t		prefix_size;					/* length of prefix */
+	size_t		message_size;					/* size of the message */
+	char		message[FLEXIBLE_ARRAY_MEMBER];	/* message including the null
+												 * terminated prefix of length
+												 * prefix_size */
+} xl_logical_message;
+
+#define SizeOfLogicalMessage	(offsetof(xl_logical_message, message))
+
+extern XLogRecPtr LogLogicalMessage(const char *prefix, const char *message,
+									size_t size, bool transactional);
+
+/* RMGR API*/
+#define XLOG_LOGICAL_MESSAGE	0x00
+void		logicalmsg_redo(XLogReaderState *record);
+void		logicalmsg_desc(StringInfo buf, XLogReaderState *record);
+const char *logicalmsg_identify(uint8 info);
+
+#endif   /* PG_LOGICAL_MESSAGE_H */
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 577b12e..fb5b758 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -74,6 +74,17 @@ typedef void (*LogicalDecodeCommitCB) (
 												   XLogRecPtr commit_lsn);
 
 /*
+ * Called for the generic logical decoding messages.
+ */
+typedef void (*LogicalDecodeMessageCB) (
+											 struct LogicalDecodingContext *,
+											 ReorderBufferTXN *txn,
+											 XLogRecPtr message_lsn,
+											 const char *prefix,
+											 Size message_size,
+											 const char *message);
+
+/*
  * Filter changes by origin.
  */
 typedef bool (*LogicalDecodeFilterByOriginCB) (
@@ -96,6 +107,7 @@ typedef struct OutputPluginCallbacks
 	LogicalDecodeBeginCB begin_cb;
 	LogicalDecodeChangeCB change_cb;
 	LogicalDecodeCommitCB commit_cb;
+	LogicalDecodeMessageCB message_cb;
 	LogicalDecodeFilterByOriginCB filter_by_origin_cb;
 	LogicalDecodeShutdownCB shutdown_cb;
 } OutputPluginCallbacks;
diff --git a/src/include/replication/reorderbuffer.h b/src/include/replication/reorderbuffer.h
index b52d06a..37c6c4b 100644
--- a/src/include/replication/reorderbuffer.h
+++ b/src/include/replication/reorderbuffer.h
@@ -54,6 +54,7 @@ enum ReorderBufferChangeType
 	REORDER_BUFFER_CHANGE_INSERT,
 	REORDER_BUFFER_CHANGE_UPDATE,
 	REORDER_BUFFER_CHANGE_DELETE,
+	REORDER_BUFFER_CHANGE_MESSAGE,
 	REORDER_BUFFER_CHANGE_INTERNAL_SNAPSHOT,
 	REORDER_BUFFER_CHANGE_INTERNAL_COMMAND_ID,
 	REORDER_BUFFER_CHANGE_INTERNAL_TUPLECID,
@@ -98,6 +99,14 @@ typedef struct ReorderBufferChange
 			ReorderBufferTupleBuf *newtuple;
 		}			tp;
 
+		/* Message with arbitrary data. */
+		struct
+		{
+			char   *prefix;
+			Size	message_size;
+			char   *message;
+		} msg;
+
 		/* New snapshot, set when action == *_INTERNAL_SNAPSHOT */
 		Snapshot	snapshot;
 
@@ -274,6 +283,14 @@ typedef void (*ReorderBufferCommitCB) (
 												   ReorderBufferTXN *txn,
 												   XLogRecPtr commit_lsn);
 
+/* message callback signature */
+typedef void (*ReorderBufferMessageCB) (
+												   ReorderBuffer *rb,
+												   ReorderBufferTXN *txn,
+												   XLogRecPtr message_lsn,
+												   const char *prefix, Size sz,
+												   const char *message);
+
 struct ReorderBuffer
 {
 	/*
@@ -300,6 +317,7 @@ struct ReorderBuffer
 	ReorderBufferBeginCB begin;
 	ReorderBufferApplyChangeCB apply_change;
 	ReorderBufferCommitCB commit;
+	ReorderBufferMessageCB message;
 
 	/*
 	 * Pointer that will be passed untouched to the callbacks.
@@ -350,6 +368,8 @@ ReorderBufferChange *ReorderBufferGetChange(ReorderBuffer *);
 void		ReorderBufferReturnChange(ReorderBuffer *, ReorderBufferChange *);
 
 void		ReorderBufferQueueChange(ReorderBuffer *, TransactionId, XLogRecPtr lsn, ReorderBufferChange *);
+void		ReorderBufferQueueMessage(ReorderBuffer *, TransactionId, XLogRecPtr lsn,
+									  const char *prefix, Size msg_sz, const char *msg);
 void ReorderBufferCommit(ReorderBuffer *, TransactionId,
 					XLogRecPtr commit_lsn, XLogRecPtr end_lsn,
 	  TimestampTz commit_time, RepOriginId origin_id, XLogRecPtr origin_lsn);
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index 75955af..c4127a1 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -63,6 +63,8 @@ extern const char *SnapBuildExportSnapshot(SnapBuild *snapstate);
 extern void SnapBuildClearExportedSnapshot(void);
 
 extern SnapBuildState SnapBuildCurrentState(SnapBuild *snapstate);
+extern Snapshot SnapBuildGetOrBuildSnapshot(SnapBuild *builder,
+											TransactionId xid);
 
 extern bool SnapBuildXactNeedsSkip(SnapBuild *snapstate, XLogRecPtr ptr);
 
-- 
1.9.1

From 6076cb5d85cab4cfe4cb99499ed49e5a0c384033 Mon Sep 17 00:00:00 2001
From: Petr Jelinek <pjmodos@pjmodos.net>
Date: Wed, 24 Feb 2016 17:02:36 +0100
Subject: [PATCH] Logical Decoding Messages

---
 contrib/test_decoding/Makefile                  |   2 +-
 contrib/test_decoding/expected/ddl.out          |  21 ++--
 contrib/test_decoding/expected/messages.out     |  56 +++++++++++
 contrib/test_decoding/sql/ddl.sql               |   3 +-
 contrib/test_decoding/sql/messages.sql          |  17 ++++
 contrib/test_decoding/test_decoding.c           |  18 ++++
 doc/src/sgml/func.sgml                          |  45 +++++++++
 doc/src/sgml/logicaldecoding.sgml               |  38 ++++++++
 src/backend/access/rmgrdesc/Makefile            |   4 +-
 src/backend/access/rmgrdesc/logicalmsgdesc.c    |  41 ++++++++
 src/backend/access/transam/rmgr.c               |   1 +
 src/backend/replication/logical/Makefile        |   2 +-
 src/backend/replication/logical/decode.c        |  46 +++++++++
 src/backend/replication/logical/logical.c       |  38 ++++++++
 src/backend/replication/logical/logicalfuncs.c  |  27 ++++++
 src/backend/replication/logical/message.c       |  85 +++++++++++++++++
 src/backend/replication/logical/reorderbuffer.c | 121 ++++++++++++++++++++++++
 src/backend/replication/logical/snapbuild.c     |  19 ++++
 src/bin/pg_xlogdump/.gitignore                  |  20 +---
 src/bin/pg_xlogdump/rmgrdesc.c                  |   1 +
 src/include/access/rmgrlist.h                   |   1 +
 src/include/catalog/pg_proc.h                   |   4 +
 src/include/replication/logicalfuncs.h          |   2 +
 src/include/replication/message.h               |  41 ++++++++
 src/include/replication/output_plugin.h         |  13 +++
 src/include/replication/reorderbuffer.h         |  22 +++++
 src/include/replication/snapbuild.h             |   2 +
 27 files changed, 659 insertions(+), 31 deletions(-)
 create mode 100644 contrib/test_decoding/expected/messages.out
 create mode 100644 contrib/test_decoding/sql/messages.sql
 create mode 100644 src/backend/access/rmgrdesc/logicalmsgdesc.c
 create mode 100644 src/backend/replication/logical/message.c
 create mode 100644 src/include/replication/message.h

diff --git a/contrib/test_decoding/Makefile b/contrib/test_decoding/Makefile
index 06c9546..309cb0b 100644
--- a/contrib/test_decoding/Makefile
+++ b/contrib/test_decoding/Makefile
@@ -38,7 +38,7 @@ submake-test_decoding:
 	$(MAKE) -C $(top_builddir)/contrib/test_decoding
 
 REGRESSCHECKS=ddl xact rewrite toast permissions decoding_in_xact \
-	decoding_into_rel binary prepared replorigin time
+	decoding_into_rel binary prepared replorigin time messages
 
 regresscheck: | submake-regress submake-test_decoding temp-install
 	$(MKDIR_P) regression_output
diff --git a/contrib/test_decoding/expected/ddl.out b/contrib/test_decoding/expected/ddl.out
index 77719e8..32cd24d 100644
--- a/contrib/test_decoding/expected/ddl.out
+++ b/contrib/test_decoding/expected/ddl.out
@@ -220,11 +220,17 @@ SELECT data FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'inc
 (7 rows)
 
 /*
- * check that disk spooling works
+ * check that disk spooling works (also for logical messages)
  */
 BEGIN;
 CREATE TABLE tr_etoomuch (id serial primary key, data int);
 INSERT INTO tr_etoomuch(data) SELECT g.i FROM generate_series(1, 10234) g(i);
+SELECT 'tx logical msg' FROM pg_logical_emit_message(true, 'test', 'tx logical msg');
+    ?column?    
+----------------
+ tx logical msg
+(1 row)
+
 DELETE FROM tr_etoomuch WHERE id < 5000;
 UPDATE tr_etoomuch SET data = - data WHERE id > 5000;
 COMMIT;
@@ -233,12 +239,13 @@ SELECT count(*), min(data), max(data)
 FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'include-xids', '0', 'skip-empty-xacts', '1')
 GROUP BY substring(data, 1, 24)
 ORDER BY 1,2;
- count |                       min                       |                                  max                                   
--------+-------------------------------------------------+------------------------------------------------------------------------
-     1 | BEGIN                                           | BEGIN
-     1 | COMMIT                                          | COMMIT
- 20467 | table public.tr_etoomuch: DELETE: id[integer]:1 | table public.tr_etoomuch: UPDATE: id[integer]:9999 data[integer]:-9999
-(3 rows)
+ count |                                  min                                  |                                  max                                   
+-------+-----------------------------------------------------------------------+------------------------------------------------------------------------
+     1 | BEGIN                                                                 | BEGIN
+     1 | COMMIT                                                                | COMMIT
+     1 | message: transactional: 1 prefix: test, sz: 14 content:tx logical msg | message: transactional: 1 prefix: test, sz: 14 content:tx logical msg
+ 20467 | table public.tr_etoomuch: DELETE: id[integer]:1                       | table public.tr_etoomuch: UPDATE: id[integer]:9999 data[integer]:-9999
+(4 rows)
 
 -- check updates of primary keys work correctly
 BEGIN;
diff --git a/contrib/test_decoding/expected/messages.out b/contrib/test_decoding/expected/messages.out
new file mode 100644
index 0000000..7fa8256
--- /dev/null
+++ b/contrib/test_decoding/expected/messages.out
@@ -0,0 +1,56 @@
+-- predictability
+SET synchronous_commit = on;
+SELECT 'init' FROM pg_create_logical_replication_slot('regression_slot', 'test_decoding');
+ ?column? 
+----------
+ init
+(1 row)
+
+SELECT 'msg1' FROM pg_logical_emit_message(true, 'test', 'msg1');
+ ?column? 
+----------
+ msg1
+(1 row)
+
+SELECT 'msg2' FROM pg_logical_emit_message(false, 'test', 'msg2');
+ ?column? 
+----------
+ msg2
+(1 row)
+
+BEGIN;
+SELECT 'msg3' FROM pg_logical_emit_message(true, 'test', 'msg3');
+ ?column? 
+----------
+ msg3
+(1 row)
+
+SELECT 'msg4' FROM pg_logical_emit_message(false, 'test', 'msg4');
+ ?column? 
+----------
+ msg4
+(1 row)
+
+SELECT 'msg5' FROM pg_logical_emit_message(true, 'test', 'msg5');
+ ?column? 
+----------
+ msg5
+(1 row)
+
+COMMIT;
+SELECT data FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'force-binary', '0', 'skip-empty-xacts', '1');
+                            data                            
+------------------------------------------------------------
+ message: transactional: 1 prefix: test, sz: 4 content:msg1
+ message: transactional: 0 prefix: test, sz: 4 content:msg2
+ message: transactional: 0 prefix: test, sz: 4 content:msg4
+ message: transactional: 1 prefix: test, sz: 4 content:msg3
+ message: transactional: 1 prefix: test, sz: 4 content:msg5
+(5 rows)
+
+SELECT 'init' FROM pg_drop_replication_slot('regression_slot');
+ ?column? 
+----------
+ init
+(1 row)
+
diff --git a/contrib/test_decoding/sql/ddl.sql b/contrib/test_decoding/sql/ddl.sql
index ad928ad..b1f7bf6 100644
--- a/contrib/test_decoding/sql/ddl.sql
+++ b/contrib/test_decoding/sql/ddl.sql
@@ -108,11 +108,12 @@ DELETE FROM tr_pkey;
 SELECT data FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'include-xids', '0', 'skip-empty-xacts', '1');
 
 /*
- * check that disk spooling works
+ * check that disk spooling works (also for logical messages)
  */
 BEGIN;
 CREATE TABLE tr_etoomuch (id serial primary key, data int);
 INSERT INTO tr_etoomuch(data) SELECT g.i FROM generate_series(1, 10234) g(i);
+SELECT 'tx logical msg' FROM pg_logical_emit_message(true, 'test', 'tx logical msg');
 DELETE FROM tr_etoomuch WHERE id < 5000;
 UPDATE tr_etoomuch SET data = - data WHERE id > 5000;
 COMMIT;
diff --git a/contrib/test_decoding/sql/messages.sql b/contrib/test_decoding/sql/messages.sql
new file mode 100644
index 0000000..8744eb6
--- /dev/null
+++ b/contrib/test_decoding/sql/messages.sql
@@ -0,0 +1,17 @@
+-- predictability
+SET synchronous_commit = on;
+
+SELECT 'init' FROM pg_create_logical_replication_slot('regression_slot', 'test_decoding');
+
+SELECT 'msg1' FROM pg_logical_emit_message(true, 'test', 'msg1');
+SELECT 'msg2' FROM pg_logical_emit_message(false, 'test', 'msg2');
+
+BEGIN;
+SELECT 'msg3' FROM pg_logical_emit_message(true, 'test', 'msg3');
+SELECT 'msg4' FROM pg_logical_emit_message(false, 'test', 'msg4');
+SELECT 'msg5' FROM pg_logical_emit_message(true, 'test', 'msg5');
+COMMIT;
+
+SELECT data FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'force-binary', '0', 'skip-empty-xacts', '1');
+
+SELECT 'init' FROM pg_drop_replication_slot('regression_slot');
diff --git a/contrib/test_decoding/test_decoding.c b/contrib/test_decoding/test_decoding.c
index 4cf808f..3336e1e 100644
--- a/contrib/test_decoding/test_decoding.c
+++ b/contrib/test_decoding/test_decoding.c
@@ -21,6 +21,7 @@
 
 #include "replication/output_plugin.h"
 #include "replication/logical.h"
+#include "replication/message.h"
 #include "replication/origin.h"
 
 #include "utils/builtins.h"
@@ -63,6 +64,10 @@ static void pg_decode_change(LogicalDecodingContext *ctx,
 				 ReorderBufferChange *change);
 static bool pg_decode_filter(LogicalDecodingContext *ctx,
 				 RepOriginId origin_id);
+static void pg_decode_message(LogicalDecodingContext *ctx,
+							  ReorderBufferTXN *txn, XLogRecPtr message_lsn,
+							  bool transactional, const char *prefix,
+							  Size sz, const char *message);
 
 void
 _PG_init(void)
@@ -82,6 +87,7 @@ _PG_output_plugin_init(OutputPluginCallbacks *cb)
 	cb->commit_cb = pg_decode_commit_txn;
 	cb->filter_by_origin_cb = pg_decode_filter;
 	cb->shutdown_cb = pg_decode_shutdown;
+	cb->message_cb = pg_decode_message;
 }
 
 
@@ -471,3 +477,15 @@ pg_decode_change(LogicalDecodingContext *ctx, ReorderBufferTXN *txn,
 
 	OutputPluginWrite(ctx, true);
 }
+
+static void
+pg_decode_message(LogicalDecodingContext *ctx,
+				  ReorderBufferTXN *txn, XLogRecPtr lsn, bool transactional,
+				  const char *prefix, Size sz, const char *message)
+{
+	OutputPluginPrepareWrite(ctx, true);
+	appendStringInfo(ctx->out, "message: transactional: %d prefix: %s, sz: %zu content:",
+					 transactional, prefix, sz);
+	appendBinaryStringInfo(ctx->out, message, sz);
+	OutputPluginWrite(ctx, true);
+}
diff --git a/doc/src/sgml/func.sgml b/doc/src/sgml/func.sgml
index ae93e69..7ac71d1 100644
--- a/doc/src/sgml/func.sgml
+++ b/doc/src/sgml/func.sgml
@@ -18238,6 +18238,51 @@ postgres=# SELECT * FROM pg_xlogfile_name_offset(pg_stop_backup());
        </entry>
       </row>
 
+      <row>
+       <entry id="pg-logical-emit-message-text">
+        <indexterm>
+         <primary>pg_logical_emit_message</primary>
+        </indexterm>
+        <literal><function>pg_logical_emit_message(<parameter>transactional</parameter> <type>bool</type>, <parameter>prefix</parameter> <type>text</type>, <parameter>content</parameter> <type>text</type>)</function></literal>
+       </entry>
+       <entry>
+        void
+       </entry>
+       <entry>
+        Emit text logical decoding message. This can be used to pass generic
+        messages to logical decoding plugins through WAL. The parameter
+        <parameter>transactional</parameter> specifies if the message should
+        be part of current transaction or if it should be written immediately
+        and decoded as soon as the logical decoding reads the record. The
+        <parameter>prefix</parameter> is textual prefix used by the logical
+        decoding plugins to easily recognize interesting messages for them.
+        The <parameter>content</parameter> is the text of the message.
+       </entry>
+      </row>
+
+      <row>
+       <entry id="pg-logical-emit-message-bytea">
+        <indexterm>
+         <primary>>pg_logical_emit_message</primary>
+        </indexterm>
+        <literal><function>>pg_logical_emit_message(<parameter>transactional</parameter> <type>bool</type>, <parameter>prefix</parameter> <type>text</type>, <parameter>content</parameter> <type>bytea</type>)</function></literal>
+       </entry>
+       <entry>
+        void
+       </entry>
+       <entry>
+        Emit binary logical decoding message. This can be used to pass generic
+        messages to logical decoding plugins through WAL. The parameter
+        <parameter>transactional</parameter> specifies if the message should
+        be part of current transaction or if it should be written immediately
+        and decoded as soon as the logical decoding reads the record. The
+        <parameter>prefix</parameter> is textual prefix used by the logical
+        decoding plugins to easily recognize interesting messages for them.
+        The <parameter>content</parameter> is the binary content of the
+        message.
+       </entry>
+      </row>
+
      </tbody>
     </tgroup>
    </table>
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 45fdfeb..dd67c8f 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -363,6 +363,7 @@ typedef struct OutputPluginCallbacks
     LogicalDecodeBeginCB begin_cb;
     LogicalDecodeChangeCB change_cb;
     LogicalDecodeCommitCB commit_cb;
+    LogicalDecodeMessageCB message_cb;
     LogicalDecodeFilterByOriginCB filter_by_origin_cb;
     LogicalDecodeShutdownCB shutdown_cb;
 } OutputPluginCallbacks;
@@ -602,6 +603,43 @@ typedef bool (*LogicalDecodeFilterByOriginCB) (
        more efficient.
      </para>
      </sect3>
+
+    <sect3 id="logicaldecoding-output-plugin-message">
+     <title>Generic Message Callback</title>
+
+     <para>
+      The optional <function>message_cb</function> callback is called whenever
+      a logical decoding message has been decoded.
+<programlisting>
+typedef void (*LogicalDecodeMessageCB) (
+    struct LogicalDecodingContext *,
+    ReorderBufferTXN *txn,
+    XLogRecPtr message_lsn,
+    bool transactional,
+    const char *prefix,
+    Size message_size,
+    const char *message
+);
+</programlisting>
+      The <parameter>txn</parameter> parameter contains meta information about
+      the transaction, like the time stamp at which it has been committed and
+      its XID. Note however that it can be NULL when the message is
+      non-transactional and the XID was not assigned yet in the transaction
+      which logged the message. The <parameter>lsn</parameter> has WAL
+      position of the message. The <parameter>transactional</parameter> says
+      if he message was sent as transactional or not.
+      The <parameter>prefix</parameter> is arbitrary null-terminated prefix
+      which can be used for identifying interesting messages for the current
+      plugin. And finally the <parameter>message</parameter> parameter holds
+      the actual message of <parameter>message_size</parameter> size.
+     </para>
+     <para>
+      Extra care should be taken to ensure that the prefix the output plugin
+      considers interesting is unique. Using name of the extension or the
+      output plugin itself is often a good choice.
+     </para>
+    </sect3>
+
    </sect2>
 
    <sect2 id="logicaldecoding-output-plugin-output">
diff --git a/src/backend/access/rmgrdesc/Makefile b/src/backend/access/rmgrdesc/Makefile
index c72a1f2..723b4d8 100644
--- a/src/backend/access/rmgrdesc/Makefile
+++ b/src/backend/access/rmgrdesc/Makefile
@@ -9,8 +9,8 @@ top_builddir = ../../../..
 include $(top_builddir)/src/Makefile.global
 
 OBJS = brindesc.o clogdesc.o committsdesc.o dbasedesc.o gindesc.o gistdesc.o \
-	   hashdesc.o heapdesc.o mxactdesc.o nbtdesc.o relmapdesc.o \
-	   replorigindesc.o seqdesc.o smgrdesc.o spgdesc.o \
+	   hashdesc.o heapdesc.o logicalmsgdesc.o mxactdesc.o nbtdesc.o \
+	   relmapdesc.o replorigindesc.o seqdesc.o smgrdesc.o spgdesc.o \
 	   standbydesc.o tblspcdesc.o xactdesc.o xlogdesc.o
 
 include $(top_srcdir)/src/backend/common.mk
diff --git a/src/backend/access/rmgrdesc/logicalmsgdesc.c b/src/backend/access/rmgrdesc/logicalmsgdesc.c
new file mode 100644
index 0000000..b194e14
--- /dev/null
+++ b/src/backend/access/rmgrdesc/logicalmsgdesc.c
@@ -0,0 +1,41 @@
+/*-------------------------------------------------------------------------
+ *
+ * logicalmsgdesc.c
+ *	  rmgr descriptor routines for replication/logical/message.c
+ *
+ * Portions Copyright (c) 2015-2016, PostgreSQL Global Development Group
+ *
+ *
+ * IDENTIFICATION
+ *	  src/backend/access/rmgrdesc/logicalmsgdesc.c
+ *
+ *-------------------------------------------------------------------------
+ */
+#include "postgres.h"
+
+#include "replication/message.h"
+
+void
+logicalmsg_desc(StringInfo buf, XLogReaderState *record)
+{
+	char	   *rec = XLogRecGetData(record);
+	uint8		info = XLogRecGetInfo(record) & ~XLR_INFO_MASK;
+
+	if (info == XLOG_LOGICAL_MESSAGE)
+	{
+		xl_logical_message *xlrec = (xl_logical_message *) rec;
+
+		appendStringInfo(buf, "%s message size %zu bytes",
+				   xlrec->transactional ? "transactional" : "nontransactional",
+						 xlrec->message_size);
+	}
+}
+
+const char *
+logicalmsg_identify(uint8 info)
+{
+	if ((info & ~XLR_INFO_MASK) == XLOG_LOGICAL_MESSAGE)
+		return "MESSAGE";
+
+	return NULL;
+}
diff --git a/src/backend/access/transam/rmgr.c b/src/backend/access/transam/rmgr.c
index 7c4d773..1a42121 100644
--- a/src/backend/access/transam/rmgr.c
+++ b/src/backend/access/transam/rmgr.c
@@ -23,6 +23,7 @@
 #include "commands/dbcommands_xlog.h"
 #include "commands/sequence.h"
 #include "commands/tablespace.h"
+#include "replication/message.h"
 #include "replication/origin.h"
 #include "storage/standby.h"
 #include "utils/relmapper.h"
diff --git a/src/backend/replication/logical/Makefile b/src/backend/replication/logical/Makefile
index 8adea13..1d7ca06 100644
--- a/src/backend/replication/logical/Makefile
+++ b/src/backend/replication/logical/Makefile
@@ -14,7 +14,7 @@ include $(top_builddir)/src/Makefile.global
 
 override CPPFLAGS := -I$(srcdir) $(CPPFLAGS)
 
-OBJS = decode.o logical.o logicalfuncs.o reorderbuffer.o origin.o \
+OBJS = decode.o logical.o logicalfuncs.o message.o origin.o reorderbuffer.o \
 	snapbuild.o
 
 include $(top_srcdir)/src/backend/common.mk
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index 13af485..01c96f7 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -39,6 +39,7 @@
 
 #include "replication/decode.h"
 #include "replication/logical.h"
+#include "replication/message.h"
 #include "replication/reorderbuffer.h"
 #include "replication/origin.h"
 #include "replication/snapbuild.h"
@@ -58,6 +59,7 @@ static void DecodeHeapOp(LogicalDecodingContext *ctx, XLogRecordBuffer *buf);
 static void DecodeHeap2Op(LogicalDecodingContext *ctx, XLogRecordBuffer *buf);
 static void DecodeXactOp(LogicalDecodingContext *ctx, XLogRecordBuffer *buf);
 static void DecodeStandbyOp(LogicalDecodingContext *ctx, XLogRecordBuffer *buf);
+static void DecodeLogicalMsgOp(LogicalDecodingContext *ctx, XLogRecordBuffer *buf);
 
 /* individual record(group)'s handlers */
 static void DecodeInsert(LogicalDecodingContext *ctx, XLogRecordBuffer *buf);
@@ -123,6 +125,10 @@ LogicalDecodingProcessRecord(LogicalDecodingContext *ctx, XLogReaderState *recor
 			DecodeHeapOp(ctx, &buf);
 			break;
 
+		case RM_LOGICALMSG_ID:
+			DecodeLogicalMsgOp(ctx, &buf);
+			break;
+
 			/*
 			 * Rmgrs irrelevant for logical decoding; they describe stuff not
 			 * represented in logical decoding. Add new rmgrs in rmgrlist.h's
@@ -457,6 +463,46 @@ DecodeHeapOp(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
 	}
 }
 
+/*
+ * Handle rmgr LOGICALMSG_ID records for DecodeRecordIntoReorderBuffer().
+ */
+static void
+DecodeLogicalMsgOp(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
+{
+	SnapBuild	   *builder = ctx->snapshot_builder;
+	XLogReaderState *r = buf->record;
+	TransactionId	xid = XLogRecGetXid(r);
+	uint8			info = XLogRecGetInfo(r) & ~XLR_INFO_MASK;
+	Snapshot		snapshot;
+	xl_logical_message *message;
+
+	if (info != XLOG_LOGICAL_MESSAGE)
+		elog(ERROR, "unexpected RM_LOGICALMSG_ID record type: %u", info);
+
+	ReorderBufferProcessXid(ctx->reorder, XLogRecGetXid(r), buf->origptr);
+
+	/* No point in doing anything yet. */
+	if (SnapBuildCurrentState(builder) < SNAPBUILD_FULL_SNAPSHOT)
+		return;
+
+	message = (xl_logical_message *) XLogRecGetData(r);
+
+	if (message->transactional &&
+		!SnapBuildProcessChange(builder, xid, buf->origptr))
+		return;
+	else if (!message->transactional &&
+			 (SnapBuildCurrentState(builder) != SNAPBUILD_CONSISTENT ||
+			  SnapBuildXactNeedsSkip(builder, buf->origptr)))
+		return;
+
+	snapshot = SnapBuildGetOrBuildSnapshot(builder, xid);
+	ReorderBufferQueueMessage(ctx->reorder, xid, snapshot, buf->endptr,
+							  message->transactional,
+							  message->message, /* first part of message is prefix */
+							  message->message_size,
+							  message->message + message->prefix_size);
+}
+
 static inline bool
 FilterByOrigin(LogicalDecodingContext *ctx, RepOriginId origin_id)
 {
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index 2e6d3f9..c06b2fa 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -62,6 +62,9 @@ static void commit_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
 				  XLogRecPtr commit_lsn);
 static void change_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
 				  Relation relation, ReorderBufferChange *change);
+static void message_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
+				  XLogRecPtr message_lsn, bool transactional,
+				  const char *prefix, Size message_size, const char *message);
 
 static void LoadOutputPlugin(OutputPluginCallbacks *callbacks, char *plugin);
 
@@ -178,6 +181,7 @@ StartupDecodingContext(List *output_plugin_options,
 	ctx->reorder->begin = begin_cb_wrapper;
 	ctx->reorder->apply_change = change_cb_wrapper;
 	ctx->reorder->commit = commit_cb_wrapper;
+	ctx->reorder->message = message_cb_wrapper;
 
 	ctx->out = makeStringInfo();
 	ctx->prepare_write = prepare_write;
@@ -702,6 +706,40 @@ filter_by_origin_cb_wrapper(LogicalDecodingContext *ctx, RepOriginId origin_id)
 	return ret;
 }
 
+static void
+message_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
+				   XLogRecPtr message_lsn, bool transactional,
+				   const char *prefix, Size message_size, const char *message)
+{
+	LogicalDecodingContext *ctx = cache->private_data;
+	LogicalErrorCallbackState state;
+	ErrorContextCallback errcallback;
+
+	if (ctx->callbacks.message_cb == NULL)
+		return;
+
+	/* Push callback + info on the error context stack */
+	state.ctx = ctx;
+	state.callback_name = "message";
+	state.report_location = message_lsn;
+	errcallback.callback = output_plugin_error_callback;
+	errcallback.arg = (void *) &state;
+	errcallback.previous = error_context_stack;
+	error_context_stack = &errcallback;
+
+	/* set output state */
+	ctx->accept_writes = true;
+	ctx->write_xid = txn != NULL ? txn->xid : InvalidTransactionId;
+	ctx->write_location = message_lsn;
+
+	/* do the actual work: call callback */
+	ctx->callbacks.message_cb(ctx, txn, message_lsn, transactional, prefix,
+							  message_size, message);
+
+	/* Pop the error context stack */
+	error_context_stack = errcallback.previous;
+}
+
 /*
  * Set the required catalog xmin horizon for historic snapshots in the current
  * replication slot.
diff --git a/src/backend/replication/logical/logicalfuncs.c b/src/backend/replication/logical/logicalfuncs.c
index f789fc1..552dac3 100644
--- a/src/backend/replication/logical/logicalfuncs.c
+++ b/src/backend/replication/logical/logicalfuncs.c
@@ -24,6 +24,8 @@
 #include "access/xlog_internal.h"
 #include "access/xlogutils.h"
 
+#include "access/xact.h"
+
 #include "catalog/pg_type.h"
 
 #include "nodes/makefuncs.h"
@@ -41,6 +43,7 @@
 #include "replication/decode.h"
 #include "replication/logical.h"
 #include "replication/logicalfuncs.h"
+#include "replication/message.h"
 
 #include "storage/fd.h"
 
@@ -363,3 +366,27 @@ pg_logical_slot_peek_binary_changes(PG_FUNCTION_ARGS)
 {
 	return pg_logical_slot_get_changes_guts(fcinfo, false, true);
 }
+
+
+/*
+ * SQL function for writing logical decding message into WAL.
+ */
+Datum
+pg_logical_emit_message_bytea(PG_FUNCTION_ARGS)
+{
+	bool		transactional = PG_GETARG_BOOL(0);
+	char	   *prefix = text_to_cstring(PG_GETARG_TEXT_PP(1));
+	bytea	   *data = PG_GETARG_BYTEA_PP(2);
+	XLogRecPtr	lsn;
+
+	lsn = LogLogicalMessage(prefix, VARDATA_ANY(data), VARSIZE_ANY_EXHDR(data),
+							transactional);
+	PG_RETURN_LSN(lsn);
+}
+
+Datum
+pg_logical_emit_message_text(PG_FUNCTION_ARGS)
+{
+	/* bytea and text are compatible */
+	return pg_logical_emit_message_bytea(fcinfo);
+}
diff --git a/src/backend/replication/logical/message.c b/src/backend/replication/logical/message.c
new file mode 100644
index 0000000..85c597b
--- /dev/null
+++ b/src/backend/replication/logical/message.c
@@ -0,0 +1,85 @@
+/*-------------------------------------------------------------------------
+ *
+ * message.c
+ *	  Generic logical messages.
+ *
+ * Copyright (c) 2013-2016, PostgreSQL Global Development Group
+ *
+ * IDENTIFICATION
+ *	  src/backend/replication/logical/message.c
+ *
+ * NOTES
+ *
+ * Generic logical messages allow XLOG logging of arbitrary binary blobs that
+ * get passed to the logical decoding plugin. In normal XLOG processing they
+ * are same as NOOP.
+ *
+ * These messages can be either transactional or non-transactional.
+ * Transactional messages are part of current transaction and will be sent to
+ * decoding plugin using in a same way as DML operations.
+ * Non-transactional messages are sent to the plugin at the time when the
+ * logical decoding reads them from XLOG.
+ *
+ * Every message carries prefix to avoid conflicts between different decoding
+ * plugins. The plugin authors must take extra care to use unique prefix,
+ * good options seems to be for example to use the name of the extension.
+ *
+ * ---------------------------------------------------------------------------
+ */
+
+#include "postgres.h"
+
+#include "access/xact.h"
+
+#include "catalog/indexing.h"
+
+#include "nodes/execnodes.h"
+
+#include "replication/message.h"
+#include "replication/logical.h"
+
+#include "utils/memutils.h"
+
+/*
+ * Write logical decoding message into XLog.
+ */
+XLogRecPtr
+LogLogicalMessage(const char *prefix, const char *message, size_t size,
+				  bool transactional)
+{
+	xl_logical_message	xlrec;
+
+	/*
+	 * Force xid to be allocated if we're emitting a transactional message.
+	 */
+	if (transactional)
+	{
+		Assert(IsTransactionState());
+		GetCurrentTransactionId();
+	}
+
+	xlrec.transactional = transactional;
+	xlrec.prefix_size = strlen(prefix) + 1;
+	xlrec.message_size = size;
+
+	XLogBeginInsert();
+	XLogRegisterData((char *) &xlrec, SizeOfLogicalMessage);
+	XLogRegisterData((char *) prefix, xlrec.prefix_size);
+	XLogRegisterData((char *) message, size);
+
+	return XLogInsert(RM_LOGICALMSG_ID, XLOG_LOGICAL_MESSAGE);
+}
+
+/*
+ * Redo is basically just noop for logical decoding messages.
+ */
+void
+logicalmsg_redo(XLogReaderState *record)
+{
+	uint8		info = XLogRecGetInfo(record) & ~XLR_INFO_MASK;
+
+	if (info != XLOG_LOGICAL_MESSAGE)
+			elog(PANIC, "logicalmsg_redo: unknown op code %u", info);
+
+	/* This is only interesting for logical decoding, see decode.c. */
+}
diff --git a/src/backend/replication/logical/reorderbuffer.c b/src/backend/replication/logical/reorderbuffer.c
index f2b8f4b..1420ddd 100644
--- a/src/backend/replication/logical/reorderbuffer.c
+++ b/src/backend/replication/logical/reorderbuffer.c
@@ -414,6 +414,14 @@ ReorderBufferReturnChange(ReorderBuffer *rb, ReorderBufferChange *change)
 				change->data.tp.oldtuple = NULL;
 			}
 			break;
+		case REORDER_BUFFER_CHANGE_MESSAGE:
+			if (change->data.msg.prefix != NULL)
+				pfree(change->data.msg.prefix);
+			change->data.msg.prefix = NULL;
+			if (change->data.msg.message != NULL)
+				pfree(change->data.msg.message);
+			change->data.msg.message = NULL;
+			break;
 		case REORDER_BUFFER_CHANGE_INTERNAL_SNAPSHOT:
 			if (change->data.snapshot)
 			{
@@ -627,6 +635,61 @@ ReorderBufferQueueChange(ReorderBuffer *rb, TransactionId xid, XLogRecPtr lsn,
 	ReorderBufferCheckSerializeTXN(rb, txn);
 }
 
+/*
+ * Queue message into a transaction so it can be processed upon commit.
+ */
+void
+ReorderBufferQueueMessage(ReorderBuffer *rb, TransactionId xid,
+						  Snapshot snapshot, XLogRecPtr lsn,
+						  bool transactional, const char *prefix,
+						  Size message_size, const char *message)
+{
+	if (transactional)
+	{
+		MemoryContext oldcontext;
+		ReorderBufferChange *change;
+
+		Assert(xid != InvalidTransactionId);
+
+		oldcontext = MemoryContextSwitchTo(rb->context);
+
+		change = ReorderBufferGetChange(rb);
+		change->action = REORDER_BUFFER_CHANGE_MESSAGE;
+		change->data.msg.prefix = pstrdup(prefix);
+		change->data.msg.message_size = message_size;
+		change->data.msg.message = palloc(message_size);
+		memcpy(change->data.msg.message, message, message_size);
+
+		ReorderBufferQueueChange(rb, xid, lsn, change);
+
+		MemoryContextSwitchTo(oldcontext);
+	}
+	else
+	{
+		ReorderBufferTXN   *txn = NULL;
+		volatile Snapshot	snapshot_now = snapshot;
+
+		if (xid != InvalidTransactionId)
+			txn = ReorderBufferTXNByXid(rb, xid, true, NULL, lsn, true);
+
+		/* setup snapshot to allow catalog access */
+		SetupHistoricSnapshot(snapshot_now, NULL);
+		PG_TRY();
+		{
+			rb->message(rb, txn, lsn, false, prefix, message_size, message);
+
+			TeardownHistoricSnapshot(false);
+		}
+		PG_CATCH();
+		{
+			TeardownHistoricSnapshot(true);
+			PG_RE_THROW();
+		}
+		PG_END_TRY();
+	}
+}
+
+
 static void
 AssertTXNLsnOrder(ReorderBuffer *rb)
 {
@@ -1493,6 +1556,13 @@ ReorderBufferCommit(ReorderBuffer *rb, TransactionId xid,
 					specinsert = change;
 					break;
 
+				case REORDER_BUFFER_CHANGE_MESSAGE:
+					rb->message(rb, txn, change->lsn, true,
+								change->data.msg.prefix,
+								change->data.msg.message_size,
+								change->data.msg.message);
+					break;
+
 				case REORDER_BUFFER_CHANGE_INTERNAL_SNAPSHOT:
 					/* get rid of the old */
 					TeardownHistoricSnapshot(false);
@@ -2159,6 +2229,33 @@ ReorderBufferSerializeChange(ReorderBuffer *rb, ReorderBufferTXN *txn,
 				}
 				break;
 			}
+		case REORDER_BUFFER_CHANGE_MESSAGE:
+			{
+				char	   *data;
+				Size		prefix_size = strlen(change->data.msg.prefix) + 1;
+
+				sz += prefix_size + change->data.msg.message_size +
+					sizeof(Size) + sizeof(Size);
+				ReorderBufferSerializeReserve(rb, sz);
+
+				data = ((char *) rb->outbuf) + sizeof(ReorderBufferDiskChange);
+
+				/* write the prefix including the size */
+				memcpy(data, &prefix_size, sizeof(Size));
+				data += sizeof(Size);
+				memcpy(data, change->data.msg.prefix,
+					   prefix_size);
+				data += prefix_size;
+
+				/* write the message including the size */
+				memcpy(data, &change->data.msg.message_size, sizeof(Size));
+				data += sizeof(Size);
+				memcpy(data, change->data.msg.message,
+					   change->data.msg.message_size);
+				data += change->data.msg.message_size;
+
+				break;
+			}
 		case REORDER_BUFFER_CHANGE_INTERNAL_SNAPSHOT:
 			{
 				Snapshot	snap;
@@ -2415,6 +2512,30 @@ ReorderBufferRestoreChange(ReorderBuffer *rb, ReorderBufferTXN *txn,
 			}
 
 			break;
+		case REORDER_BUFFER_CHANGE_MESSAGE:
+			{
+				Size		prefix_size;
+
+				/* read prefix */
+				memcpy(&prefix_size, data, sizeof(Size));
+				data += sizeof(Size);
+				change->data.msg.prefix = MemoryContextAlloc(rb->context,
+															 prefix_size);
+				memcpy(change->data.msg.prefix, data, prefix_size);
+				Assert(change->data.msg.prefix[prefix_size-1] == '\0');
+				data += prefix_size;
+
+				/* read the messsage */
+				memcpy(&change->data.msg.message_size, data, sizeof(Size));
+				data += sizeof(Size);
+				change->data.msg.message = MemoryContextAlloc(rb->context,
+												change->data.msg.message_size);
+				memcpy(change->data.msg.message, data,
+					   change->data.msg.message_size);
+				data += change->data.msg.message_size;
+
+				break;
+			}
 		case REORDER_BUFFER_CHANGE_INTERNAL_SNAPSHOT:
 			{
 				Snapshot	oldsnap;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index 179b85a..b4dc617 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -605,6 +605,25 @@ SnapBuildExportSnapshot(SnapBuild *builder)
 }
 
 /*
+ * Ensure there is a snapshot and if not build one for current transaction.
+ */
+Snapshot
+SnapBuildGetOrBuildSnapshot(SnapBuild *builder, TransactionId xid)
+{
+	Assert(builder->state == SNAPBUILD_CONSISTENT);
+
+	/* only build a new snapshot if we don't have a prebuilt one */
+	if (builder->snapshot == NULL)
+	{
+		builder->snapshot = SnapBuildBuildSnapshot(builder, xid);
+		/* inrease refcount for the snapshot builder */
+		SnapBuildSnapIncRefcount(builder->snapshot);
+	}
+
+	return builder->snapshot;
+}
+
+/*
  * Reset a previously SnapBuildExportSnapshot()'ed snapshot if there is
  * any. Aborts the previously started transaction and resets the resource
  * owner back to its original value.
diff --git a/src/bin/pg_xlogdump/.gitignore b/src/bin/pg_xlogdump/.gitignore
index eebaf30..c4783f1 100644
--- a/src/bin/pg_xlogdump/.gitignore
+++ b/src/bin/pg_xlogdump/.gitignore
@@ -1,22 +1,4 @@
 /pg_xlogdump
 # Source files copied from src/backend/access/rmgrdesc/
-/brindesc.c
-/clogdesc.c
-/committsdesc.c
-/dbasedesc.c
-/gindesc.c
-/gistdesc.c
-/hashdesc.c
-/heapdesc.c
-/mxactdesc.c
-/nbtdesc.c
-/relmapdesc.c
-/replorigindesc.c
-/seqdesc.c
-/smgrdesc.c
-/spgdesc.c
-/standbydesc.c
-/tblspcdesc.c
-/xactdesc.c
-/xlogdesc.c
+/*desc.c
 /xlogreader.c
diff --git a/src/bin/pg_xlogdump/rmgrdesc.c b/src/bin/pg_xlogdump/rmgrdesc.c
index f9cd395..6ba7f22 100644
--- a/src/bin/pg_xlogdump/rmgrdesc.c
+++ b/src/bin/pg_xlogdump/rmgrdesc.c
@@ -25,6 +25,7 @@
 #include "commands/dbcommands_xlog.h"
 #include "commands/sequence.h"
 #include "commands/tablespace.h"
+#include "replication/message.h"
 #include "replication/origin.h"
 #include "rmgrdesc.h"
 #include "storage/standbydefs.h"
diff --git a/src/include/access/rmgrlist.h b/src/include/access/rmgrlist.h
index fab912d..35c242d 100644
--- a/src/include/access/rmgrlist.h
+++ b/src/include/access/rmgrlist.h
@@ -45,3 +45,4 @@ PG_RMGR(RM_SPGIST_ID, "SPGist", spg_redo, spg_desc, spg_identify, spg_xlog_start
 PG_RMGR(RM_BRIN_ID, "BRIN", brin_redo, brin_desc, brin_identify, NULL, NULL)
 PG_RMGR(RM_COMMIT_TS_ID, "CommitTs", commit_ts_redo, commit_ts_desc, commit_ts_identify, NULL, NULL)
 PG_RMGR(RM_REPLORIGIN_ID, "ReplicationOrigin", replorigin_redo, replorigin_desc, replorigin_identify, NULL, NULL)
+PG_RMGR(RM_LOGICALMSG_ID, "LogicalMessage", logicalmsg_redo, logicalmsg_desc, logicalmsg_identify, NULL, NULL)
diff --git a/src/include/catalog/pg_proc.h b/src/include/catalog/pg_proc.h
index a595327..3713739 100644
--- a/src/include/catalog/pg_proc.h
+++ b/src/include/catalog/pg_proc.h
@@ -5114,6 +5114,10 @@ DATA(insert OID = 3784 (  pg_logical_slot_peek_changes PGNSP PGUID 12 1000 1000
 DESCR("peek at changes from replication slot");
 DATA(insert OID = 3785 (  pg_logical_slot_peek_binary_changes PGNSP PGUID 12 1000 1000 25 0 f f f f f t v u 4 0 2249 "19 3220 23 1009" "{19,3220,23,1009,3220,28,17}" "{i,i,i,v,o,o,o}" "{slot_name,upto_lsn,upto_nchanges,options,location,xid,data}" _null_ _null_ pg_logical_slot_peek_binary_changes _null_ _null_ _null_ ));
 DESCR("peek at binary changes from replication slot");
+DATA(insert OID = 3577 (  pg_logical_emit_message PGNSP PGUID 12 1 0 0 0 f f f f t f v u 3 0 3220 "16 25 25" _null_ _null_ _null_ _null_ _null_ pg_logical_emit_message_text _null_ _null_ _null_ ));
+DESCR("emit a textual logical decoding message");
+DATA(insert OID = 3578 (  pg_logical_emit_message PGNSP PGUID 12 1 0 0 0 f f f f t f v u 3 0 3220 "16 25 17" _null_ _null_ _null_ _null_ _null_ pg_logical_emit_message_bytea _null_ _null_ _null_ ));
+DESCR("emit a binary logical decoding message");
 
 /* event triggers */
 DATA(insert OID = 3566 (  pg_event_trigger_dropped_objects		PGNSP PGUID 12 10 100 0 0 f f f f t t s s 0 0 2249 "" "{26,26,23,16,16,16,25,25,25,25,1009,1009}" "{o,o,o,o,o,o,o,o,o,o,o,o}" "{classid, objid, objsubid, original, normal, is_temporary, object_type, schema_name, object_name, object_identity, address_names, address_args}" _null_ _null_ pg_event_trigger_dropped_objects _null_ _null_ _null_ ));
diff --git a/src/include/replication/logicalfuncs.h b/src/include/replication/logicalfuncs.h
index c87a1df..5540414 100644
--- a/src/include/replication/logicalfuncs.h
+++ b/src/include/replication/logicalfuncs.h
@@ -21,4 +21,6 @@ extern Datum pg_logical_slot_get_binary_changes(PG_FUNCTION_ARGS);
 extern Datum pg_logical_slot_peek_changes(PG_FUNCTION_ARGS);
 extern Datum pg_logical_slot_peek_binary_changes(PG_FUNCTION_ARGS);
 
+extern Datum pg_logical_emit_message_bytea(PG_FUNCTION_ARGS);
+extern Datum pg_logical_emit_message_text(PG_FUNCTION_ARGS);
 #endif
diff --git a/src/include/replication/message.h b/src/include/replication/message.h
new file mode 100644
index 0000000..8b968d5
--- /dev/null
+++ b/src/include/replication/message.h
@@ -0,0 +1,41 @@
+/*-------------------------------------------------------------------------
+ * message.h
+ *	   Exports from replication/logical/message.c
+ *
+ * Copyright (c) 2013-2016, PostgreSQL Global Development Group
+ *
+ * src/include/replication/message.h
+ *-------------------------------------------------------------------------
+ */
+#ifndef PG_LOGICAL_MESSAGE_H
+#define PG_LOGICAL_MESSAGE_H
+
+#include "access/xlog.h"
+#include "access/xlogdefs.h"
+#include "access/xlogreader.h"
+
+/*
+ * Generic logical decoding message wal record.
+ */
+typedef struct xl_logical_message
+{
+	bool		transactional;					/* is message transactional? */
+	Size		prefix_size;					/* length of prefix */
+	Size		message_size;					/* size of the message */
+	char		message[FLEXIBLE_ARRAY_MEMBER];	/* message including the null
+												 * terminated prefix of length
+												 * prefix_size */
+} xl_logical_message;
+
+#define SizeOfLogicalMessage	(offsetof(xl_logical_message, message))
+
+extern XLogRecPtr LogLogicalMessage(const char *prefix, const char *message,
+									size_t size, bool transactional);
+
+/* RMGR API*/
+#define XLOG_LOGICAL_MESSAGE	0x00
+void		logicalmsg_redo(XLogReaderState *record);
+void		logicalmsg_desc(StringInfo buf, XLogReaderState *record);
+const char *logicalmsg_identify(uint8 info);
+
+#endif   /* PG_LOGICAL_MESSAGE_H */
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 577b12e..3a2ca98 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -74,6 +74,18 @@ typedef void (*LogicalDecodeCommitCB) (
 												   XLogRecPtr commit_lsn);
 
 /*
+ * Called for the generic logical decoding messages.
+ */
+typedef void (*LogicalDecodeMessageCB) (
+											 struct LogicalDecodingContext *,
+											 ReorderBufferTXN *txn,
+											 XLogRecPtr message_lsn,
+											 bool transactional,
+											 const char *prefix,
+											 Size message_size,
+											 const char *message);
+
+/*
  * Filter changes by origin.
  */
 typedef bool (*LogicalDecodeFilterByOriginCB) (
@@ -96,6 +108,7 @@ typedef struct OutputPluginCallbacks
 	LogicalDecodeBeginCB begin_cb;
 	LogicalDecodeChangeCB change_cb;
 	LogicalDecodeCommitCB commit_cb;
+	LogicalDecodeMessageCB message_cb;
 	LogicalDecodeFilterByOriginCB filter_by_origin_cb;
 	LogicalDecodeShutdownCB shutdown_cb;
 } OutputPluginCallbacks;
diff --git a/src/include/replication/reorderbuffer.h b/src/include/replication/reorderbuffer.h
index b52d06a..4c54953 100644
--- a/src/include/replication/reorderbuffer.h
+++ b/src/include/replication/reorderbuffer.h
@@ -54,6 +54,7 @@ enum ReorderBufferChangeType
 	REORDER_BUFFER_CHANGE_INSERT,
 	REORDER_BUFFER_CHANGE_UPDATE,
 	REORDER_BUFFER_CHANGE_DELETE,
+	REORDER_BUFFER_CHANGE_MESSAGE,
 	REORDER_BUFFER_CHANGE_INTERNAL_SNAPSHOT,
 	REORDER_BUFFER_CHANGE_INTERNAL_COMMAND_ID,
 	REORDER_BUFFER_CHANGE_INTERNAL_TUPLECID,
@@ -98,6 +99,14 @@ typedef struct ReorderBufferChange
 			ReorderBufferTupleBuf *newtuple;
 		}			tp;
 
+		/* Message with arbitrary data. */
+		struct
+		{
+			char   *prefix;
+			Size	message_size;
+			char   *message;
+		} msg;
+
 		/* New snapshot, set when action == *_INTERNAL_SNAPSHOT */
 		Snapshot	snapshot;
 
@@ -274,6 +283,15 @@ typedef void (*ReorderBufferCommitCB) (
 												   ReorderBufferTXN *txn,
 												   XLogRecPtr commit_lsn);
 
+/* message callback signature */
+typedef void (*ReorderBufferMessageCB) (
+												   ReorderBuffer *rb,
+												   ReorderBufferTXN *txn,
+												   XLogRecPtr message_lsn,
+												   bool transactional,
+												   const char *prefix, Size sz,
+												   const char *message);
+
 struct ReorderBuffer
 {
 	/*
@@ -300,6 +318,7 @@ struct ReorderBuffer
 	ReorderBufferBeginCB begin;
 	ReorderBufferApplyChangeCB apply_change;
 	ReorderBufferCommitCB commit;
+	ReorderBufferMessageCB message;
 
 	/*
 	 * Pointer that will be passed untouched to the callbacks.
@@ -350,6 +369,9 @@ ReorderBufferChange *ReorderBufferGetChange(ReorderBuffer *);
 void		ReorderBufferReturnChange(ReorderBuffer *, ReorderBufferChange *);
 
 void		ReorderBufferQueueChange(ReorderBuffer *, TransactionId, XLogRecPtr lsn, ReorderBufferChange *);
+void		ReorderBufferQueueMessage(ReorderBuffer *, TransactionId, Snapshot snapshot, XLogRecPtr lsn,
+									  bool transactional, const char *prefix,
+									  Size message_size, const char *message);
 void ReorderBufferCommit(ReorderBuffer *, TransactionId,
 					XLogRecPtr commit_lsn, XLogRecPtr end_lsn,
 	  TimestampTz commit_time, RepOriginId origin_id, XLogRecPtr origin_lsn);
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index 75955af..c4127a1 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -63,6 +63,8 @@ extern const char *SnapBuildExportSnapshot(SnapBuild *snapstate);
 extern void SnapBuildClearExportedSnapshot(void);
 
 extern SnapBuildState SnapBuildCurrentState(SnapBuild *snapstate);
+extern Snapshot SnapBuildGetOrBuildSnapshot(SnapBuild *builder,
+											TransactionId xid);
 
 extern bool SnapBuildXactNeedsSkip(SnapBuild *snapstate, XLogRecPtr ptr);
 
-- 
1.9.1

From 81fc28cedc19fe0f91f882d42989c14113a40f88 Mon Sep 17 00:00:00 2001
From: Petr Jelinek <pjmodos@pjmodos.net>
Date: Wed, 24 Feb 2016 17:02:36 +0100
Subject: [PATCH] Logical Decoding Messages

---
 contrib/test_decoding/Makefile                  |   2 +-
 contrib/test_decoding/expected/ddl.out          |  21 ++--
 contrib/test_decoding/expected/messages.out     |  71 ++++++++++++++
 contrib/test_decoding/sql/ddl.sql               |   3 +-
 contrib/test_decoding/sql/messages.sql          |  22 +++++
 contrib/test_decoding/test_decoding.c           |  18 ++++
 doc/src/sgml/func.sgml                          |  45 +++++++++
 doc/src/sgml/logicaldecoding.sgml               |  38 ++++++++
 src/backend/access/rmgrdesc/Makefile            |   4 +-
 src/backend/access/rmgrdesc/logicalmsgdesc.c    |  41 ++++++++
 src/backend/access/transam/rmgr.c               |   1 +
 src/backend/replication/logical/Makefile        |   2 +-
 src/backend/replication/logical/decode.c        |  46 +++++++++
 src/backend/replication/logical/logical.c       |  38 ++++++++
 src/backend/replication/logical/logicalfuncs.c  |  27 ++++++
 src/backend/replication/logical/message.c       |  85 +++++++++++++++++
 src/backend/replication/logical/reorderbuffer.c | 121 ++++++++++++++++++++++++
 src/backend/replication/logical/snapbuild.c     |  19 ++++
 src/bin/pg_xlogdump/.gitignore                  |  20 +---
 src/bin/pg_xlogdump/rmgrdesc.c                  |   1 +
 src/include/access/rmgrlist.h                   |   1 +
 src/include/catalog/pg_proc.h                   |   4 +
 src/include/replication/logicalfuncs.h          |   2 +
 src/include/replication/message.h               |  41 ++++++++
 src/include/replication/output_plugin.h         |  13 +++
 src/include/replication/reorderbuffer.h         |  22 +++++
 src/include/replication/snapbuild.h             |   2 +
 27 files changed, 679 insertions(+), 31 deletions(-)
 create mode 100644 contrib/test_decoding/expected/messages.out
 create mode 100644 contrib/test_decoding/sql/messages.sql
 create mode 100644 src/backend/access/rmgrdesc/logicalmsgdesc.c
 create mode 100644 src/backend/replication/logical/message.c
 create mode 100644 src/include/replication/message.h

diff --git a/contrib/test_decoding/Makefile b/contrib/test_decoding/Makefile
index 06c9546..309cb0b 100644
--- a/contrib/test_decoding/Makefile
+++ b/contrib/test_decoding/Makefile
@@ -38,7 +38,7 @@ submake-test_decoding:
 	$(MAKE) -C $(top_builddir)/contrib/test_decoding
 
 REGRESSCHECKS=ddl xact rewrite toast permissions decoding_in_xact \
-	decoding_into_rel binary prepared replorigin time
+	decoding_into_rel binary prepared replorigin time messages
 
 regresscheck: | submake-regress submake-test_decoding temp-install
 	$(MKDIR_P) regression_output
diff --git a/contrib/test_decoding/expected/ddl.out b/contrib/test_decoding/expected/ddl.out
index 77719e8..32cd24d 100644
--- a/contrib/test_decoding/expected/ddl.out
+++ b/contrib/test_decoding/expected/ddl.out
@@ -220,11 +220,17 @@ SELECT data FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'inc
 (7 rows)
 
 /*
- * check that disk spooling works
+ * check that disk spooling works (also for logical messages)
  */
 BEGIN;
 CREATE TABLE tr_etoomuch (id serial primary key, data int);
 INSERT INTO tr_etoomuch(data) SELECT g.i FROM generate_series(1, 10234) g(i);
+SELECT 'tx logical msg' FROM pg_logical_emit_message(true, 'test', 'tx logical msg');
+    ?column?    
+----------------
+ tx logical msg
+(1 row)
+
 DELETE FROM tr_etoomuch WHERE id < 5000;
 UPDATE tr_etoomuch SET data = - data WHERE id > 5000;
 COMMIT;
@@ -233,12 +239,13 @@ SELECT count(*), min(data), max(data)
 FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'include-xids', '0', 'skip-empty-xacts', '1')
 GROUP BY substring(data, 1, 24)
 ORDER BY 1,2;
- count |                       min                       |                                  max                                   
--------+-------------------------------------------------+------------------------------------------------------------------------
-     1 | BEGIN                                           | BEGIN
-     1 | COMMIT                                          | COMMIT
- 20467 | table public.tr_etoomuch: DELETE: id[integer]:1 | table public.tr_etoomuch: UPDATE: id[integer]:9999 data[integer]:-9999
-(3 rows)
+ count |                                  min                                  |                                  max                                   
+-------+-----------------------------------------------------------------------+------------------------------------------------------------------------
+     1 | BEGIN                                                                 | BEGIN
+     1 | COMMIT                                                                | COMMIT
+     1 | message: transactional: 1 prefix: test, sz: 14 content:tx logical msg | message: transactional: 1 prefix: test, sz: 14 content:tx logical msg
+ 20467 | table public.tr_etoomuch: DELETE: id[integer]:1                       | table public.tr_etoomuch: UPDATE: id[integer]:9999 data[integer]:-9999
+(4 rows)
 
 -- check updates of primary keys work correctly
 BEGIN;
diff --git a/contrib/test_decoding/expected/messages.out b/contrib/test_decoding/expected/messages.out
new file mode 100644
index 0000000..2edbf2f
--- /dev/null
+++ b/contrib/test_decoding/expected/messages.out
@@ -0,0 +1,71 @@
+-- predictability
+SET synchronous_commit = on;
+SELECT 'init' FROM pg_create_logical_replication_slot('regression_slot', 'test_decoding');
+ ?column? 
+----------
+ init
+(1 row)
+
+SELECT 'msg1' FROM pg_logical_emit_message(true, 'test', 'msg1');
+ ?column? 
+----------
+ msg1
+(1 row)
+
+SELECT 'msg2' FROM pg_logical_emit_message(false, 'test', 'msg2');
+ ?column? 
+----------
+ msg2
+(1 row)
+
+BEGIN;
+SELECT 'msg3' FROM pg_logical_emit_message(true, 'test', 'msg3');
+ ?column? 
+----------
+ msg3
+(1 row)
+
+SELECT 'msg4' FROM pg_logical_emit_message(false, 'test', 'msg4');
+ ?column? 
+----------
+ msg4
+(1 row)
+
+ROLLBACK;
+BEGIN;
+SELECT 'msg5' FROM pg_logical_emit_message(true, 'test', 'msg5');
+ ?column? 
+----------
+ msg5
+(1 row)
+
+SELECT 'msg6' FROM pg_logical_emit_message(false, 'test', 'msg6');
+ ?column? 
+----------
+ msg6
+(1 row)
+
+SELECT 'msg7' FROM pg_logical_emit_message(true, 'test', 'msg7');
+ ?column? 
+----------
+ msg7
+(1 row)
+
+COMMIT;
+SELECT data FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'force-binary', '0', 'skip-empty-xacts', '1');
+                            data                            
+------------------------------------------------------------
+ message: transactional: 1 prefix: test, sz: 4 content:msg1
+ message: transactional: 0 prefix: test, sz: 4 content:msg2
+ message: transactional: 0 prefix: test, sz: 4 content:msg4
+ message: transactional: 0 prefix: test, sz: 4 content:msg6
+ message: transactional: 1 prefix: test, sz: 4 content:msg5
+ message: transactional: 1 prefix: test, sz: 4 content:msg7
+(6 rows)
+
+SELECT 'init' FROM pg_drop_replication_slot('regression_slot');
+ ?column? 
+----------
+ init
+(1 row)
+
diff --git a/contrib/test_decoding/sql/ddl.sql b/contrib/test_decoding/sql/ddl.sql
index ad928ad..b1f7bf6 100644
--- a/contrib/test_decoding/sql/ddl.sql
+++ b/contrib/test_decoding/sql/ddl.sql
@@ -108,11 +108,12 @@ DELETE FROM tr_pkey;
 SELECT data FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'include-xids', '0', 'skip-empty-xacts', '1');
 
 /*
- * check that disk spooling works
+ * check that disk spooling works (also for logical messages)
  */
 BEGIN;
 CREATE TABLE tr_etoomuch (id serial primary key, data int);
 INSERT INTO tr_etoomuch(data) SELECT g.i FROM generate_series(1, 10234) g(i);
+SELECT 'tx logical msg' FROM pg_logical_emit_message(true, 'test', 'tx logical msg');
 DELETE FROM tr_etoomuch WHERE id < 5000;
 UPDATE tr_etoomuch SET data = - data WHERE id > 5000;
 COMMIT;
diff --git a/contrib/test_decoding/sql/messages.sql b/contrib/test_decoding/sql/messages.sql
new file mode 100644
index 0000000..37bd100
--- /dev/null
+++ b/contrib/test_decoding/sql/messages.sql
@@ -0,0 +1,22 @@
+-- predictability
+SET synchronous_commit = on;
+
+SELECT 'init' FROM pg_create_logical_replication_slot('regression_slot', 'test_decoding');
+
+SELECT 'msg1' FROM pg_logical_emit_message(true, 'test', 'msg1');
+SELECT 'msg2' FROM pg_logical_emit_message(false, 'test', 'msg2');
+
+BEGIN;
+SELECT 'msg3' FROM pg_logical_emit_message(true, 'test', 'msg3');
+SELECT 'msg4' FROM pg_logical_emit_message(false, 'test', 'msg4');
+ROLLBACK;
+
+BEGIN;
+SELECT 'msg5' FROM pg_logical_emit_message(true, 'test', 'msg5');
+SELECT 'msg6' FROM pg_logical_emit_message(false, 'test', 'msg6');
+SELECT 'msg7' FROM pg_logical_emit_message(true, 'test', 'msg7');
+COMMIT;
+
+SELECT data FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'force-binary', '0', 'skip-empty-xacts', '1');
+
+SELECT 'init' FROM pg_drop_replication_slot('regression_slot');
diff --git a/contrib/test_decoding/test_decoding.c b/contrib/test_decoding/test_decoding.c
index 4cf808f..3336e1e 100644
--- a/contrib/test_decoding/test_decoding.c
+++ b/contrib/test_decoding/test_decoding.c
@@ -21,6 +21,7 @@
 
 #include "replication/output_plugin.h"
 #include "replication/logical.h"
+#include "replication/message.h"
 #include "replication/origin.h"
 
 #include "utils/builtins.h"
@@ -63,6 +64,10 @@ static void pg_decode_change(LogicalDecodingContext *ctx,
 				 ReorderBufferChange *change);
 static bool pg_decode_filter(LogicalDecodingContext *ctx,
 				 RepOriginId origin_id);
+static void pg_decode_message(LogicalDecodingContext *ctx,
+							  ReorderBufferTXN *txn, XLogRecPtr message_lsn,
+							  bool transactional, const char *prefix,
+							  Size sz, const char *message);
 
 void
 _PG_init(void)
@@ -82,6 +87,7 @@ _PG_output_plugin_init(OutputPluginCallbacks *cb)
 	cb->commit_cb = pg_decode_commit_txn;
 	cb->filter_by_origin_cb = pg_decode_filter;
 	cb->shutdown_cb = pg_decode_shutdown;
+	cb->message_cb = pg_decode_message;
 }
 
 
@@ -471,3 +477,15 @@ pg_decode_change(LogicalDecodingContext *ctx, ReorderBufferTXN *txn,
 
 	OutputPluginWrite(ctx, true);
 }
+
+static void
+pg_decode_message(LogicalDecodingContext *ctx,
+				  ReorderBufferTXN *txn, XLogRecPtr lsn, bool transactional,
+				  const char *prefix, Size sz, const char *message)
+{
+	OutputPluginPrepareWrite(ctx, true);
+	appendStringInfo(ctx->out, "message: transactional: %d prefix: %s, sz: %zu content:",
+					 transactional, prefix, sz);
+	appendBinaryStringInfo(ctx->out, message, sz);
+	OutputPluginWrite(ctx, true);
+}
diff --git a/doc/src/sgml/func.sgml b/doc/src/sgml/func.sgml
index ae93e69..7ac71d1 100644
--- a/doc/src/sgml/func.sgml
+++ b/doc/src/sgml/func.sgml
@@ -18238,6 +18238,51 @@ postgres=# SELECT * FROM pg_xlogfile_name_offset(pg_stop_backup());
        </entry>
       </row>
 
+      <row>
+       <entry id="pg-logical-emit-message-text">
+        <indexterm>
+         <primary>pg_logical_emit_message</primary>
+        </indexterm>
+        <literal><function>pg_logical_emit_message(<parameter>transactional</parameter> <type>bool</type>, <parameter>prefix</parameter> <type>text</type>, <parameter>content</parameter> <type>text</type>)</function></literal>
+       </entry>
+       <entry>
+        void
+       </entry>
+       <entry>
+        Emit text logical decoding message. This can be used to pass generic
+        messages to logical decoding plugins through WAL. The parameter
+        <parameter>transactional</parameter> specifies if the message should
+        be part of current transaction or if it should be written immediately
+        and decoded as soon as the logical decoding reads the record. The
+        <parameter>prefix</parameter> is textual prefix used by the logical
+        decoding plugins to easily recognize interesting messages for them.
+        The <parameter>content</parameter> is the text of the message.
+       </entry>
+      </row>
+
+      <row>
+       <entry id="pg-logical-emit-message-bytea">
+        <indexterm>
+         <primary>>pg_logical_emit_message</primary>
+        </indexterm>
+        <literal><function>>pg_logical_emit_message(<parameter>transactional</parameter> <type>bool</type>, <parameter>prefix</parameter> <type>text</type>, <parameter>content</parameter> <type>bytea</type>)</function></literal>
+       </entry>
+       <entry>
+        void
+       </entry>
+       <entry>
+        Emit binary logical decoding message. This can be used to pass generic
+        messages to logical decoding plugins through WAL. The parameter
+        <parameter>transactional</parameter> specifies if the message should
+        be part of current transaction or if it should be written immediately
+        and decoded as soon as the logical decoding reads the record. The
+        <parameter>prefix</parameter> is textual prefix used by the logical
+        decoding plugins to easily recognize interesting messages for them.
+        The <parameter>content</parameter> is the binary content of the
+        message.
+       </entry>
+      </row>
+
      </tbody>
     </tgroup>
    </table>
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 45fdfeb..dd67c8f 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -363,6 +363,7 @@ typedef struct OutputPluginCallbacks
     LogicalDecodeBeginCB begin_cb;
     LogicalDecodeChangeCB change_cb;
     LogicalDecodeCommitCB commit_cb;
+    LogicalDecodeMessageCB message_cb;
     LogicalDecodeFilterByOriginCB filter_by_origin_cb;
     LogicalDecodeShutdownCB shutdown_cb;
 } OutputPluginCallbacks;
@@ -602,6 +603,43 @@ typedef bool (*LogicalDecodeFilterByOriginCB) (
        more efficient.
      </para>
      </sect3>
+
+    <sect3 id="logicaldecoding-output-plugin-message">
+     <title>Generic Message Callback</title>
+
+     <para>
+      The optional <function>message_cb</function> callback is called whenever
+      a logical decoding message has been decoded.
+<programlisting>
+typedef void (*LogicalDecodeMessageCB) (
+    struct LogicalDecodingContext *,
+    ReorderBufferTXN *txn,
+    XLogRecPtr message_lsn,
+    bool transactional,
+    const char *prefix,
+    Size message_size,
+    const char *message
+);
+</programlisting>
+      The <parameter>txn</parameter> parameter contains meta information about
+      the transaction, like the time stamp at which it has been committed and
+      its XID. Note however that it can be NULL when the message is
+      non-transactional and the XID was not assigned yet in the transaction
+      which logged the message. The <parameter>lsn</parameter> has WAL
+      position of the message. The <parameter>transactional</parameter> says
+      if he message was sent as transactional or not.
+      The <parameter>prefix</parameter> is arbitrary null-terminated prefix
+      which can be used for identifying interesting messages for the current
+      plugin. And finally the <parameter>message</parameter> parameter holds
+      the actual message of <parameter>message_size</parameter> size.
+     </para>
+     <para>
+      Extra care should be taken to ensure that the prefix the output plugin
+      considers interesting is unique. Using name of the extension or the
+      output plugin itself is often a good choice.
+     </para>
+    </sect3>
+
    </sect2>
 
    <sect2 id="logicaldecoding-output-plugin-output">
diff --git a/src/backend/access/rmgrdesc/Makefile b/src/backend/access/rmgrdesc/Makefile
index c72a1f2..723b4d8 100644
--- a/src/backend/access/rmgrdesc/Makefile
+++ b/src/backend/access/rmgrdesc/Makefile
@@ -9,8 +9,8 @@ top_builddir = ../../../..
 include $(top_builddir)/src/Makefile.global
 
 OBJS = brindesc.o clogdesc.o committsdesc.o dbasedesc.o gindesc.o gistdesc.o \
-	   hashdesc.o heapdesc.o mxactdesc.o nbtdesc.o relmapdesc.o \
-	   replorigindesc.o seqdesc.o smgrdesc.o spgdesc.o \
+	   hashdesc.o heapdesc.o logicalmsgdesc.o mxactdesc.o nbtdesc.o \
+	   relmapdesc.o replorigindesc.o seqdesc.o smgrdesc.o spgdesc.o \
 	   standbydesc.o tblspcdesc.o xactdesc.o xlogdesc.o
 
 include $(top_srcdir)/src/backend/common.mk
diff --git a/src/backend/access/rmgrdesc/logicalmsgdesc.c b/src/backend/access/rmgrdesc/logicalmsgdesc.c
new file mode 100644
index 0000000..b194e14
--- /dev/null
+++ b/src/backend/access/rmgrdesc/logicalmsgdesc.c
@@ -0,0 +1,41 @@
+/*-------------------------------------------------------------------------
+ *
+ * logicalmsgdesc.c
+ *	  rmgr descriptor routines for replication/logical/message.c
+ *
+ * Portions Copyright (c) 2015-2016, PostgreSQL Global Development Group
+ *
+ *
+ * IDENTIFICATION
+ *	  src/backend/access/rmgrdesc/logicalmsgdesc.c
+ *
+ *-------------------------------------------------------------------------
+ */
+#include "postgres.h"
+
+#include "replication/message.h"
+
+void
+logicalmsg_desc(StringInfo buf, XLogReaderState *record)
+{
+	char	   *rec = XLogRecGetData(record);
+	uint8		info = XLogRecGetInfo(record) & ~XLR_INFO_MASK;
+
+	if (info == XLOG_LOGICAL_MESSAGE)
+	{
+		xl_logical_message *xlrec = (xl_logical_message *) rec;
+
+		appendStringInfo(buf, "%s message size %zu bytes",
+				   xlrec->transactional ? "transactional" : "nontransactional",
+						 xlrec->message_size);
+	}
+}
+
+const char *
+logicalmsg_identify(uint8 info)
+{
+	if ((info & ~XLR_INFO_MASK) == XLOG_LOGICAL_MESSAGE)
+		return "MESSAGE";
+
+	return NULL;
+}
diff --git a/src/backend/access/transam/rmgr.c b/src/backend/access/transam/rmgr.c
index 7c4d773..1a42121 100644
--- a/src/backend/access/transam/rmgr.c
+++ b/src/backend/access/transam/rmgr.c
@@ -23,6 +23,7 @@
 #include "commands/dbcommands_xlog.h"
 #include "commands/sequence.h"
 #include "commands/tablespace.h"
+#include "replication/message.h"
 #include "replication/origin.h"
 #include "storage/standby.h"
 #include "utils/relmapper.h"
diff --git a/src/backend/replication/logical/Makefile b/src/backend/replication/logical/Makefile
index 8adea13..1d7ca06 100644
--- a/src/backend/replication/logical/Makefile
+++ b/src/backend/replication/logical/Makefile
@@ -14,7 +14,7 @@ include $(top_builddir)/src/Makefile.global
 
 override CPPFLAGS := -I$(srcdir) $(CPPFLAGS)
 
-OBJS = decode.o logical.o logicalfuncs.o reorderbuffer.o origin.o \
+OBJS = decode.o logical.o logicalfuncs.o message.o origin.o reorderbuffer.o \
 	snapbuild.o
 
 include $(top_srcdir)/src/backend/common.mk
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index 13af485..01c96f7 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -39,6 +39,7 @@
 
 #include "replication/decode.h"
 #include "replication/logical.h"
+#include "replication/message.h"
 #include "replication/reorderbuffer.h"
 #include "replication/origin.h"
 #include "replication/snapbuild.h"
@@ -58,6 +59,7 @@ static void DecodeHeapOp(LogicalDecodingContext *ctx, XLogRecordBuffer *buf);
 static void DecodeHeap2Op(LogicalDecodingContext *ctx, XLogRecordBuffer *buf);
 static void DecodeXactOp(LogicalDecodingContext *ctx, XLogRecordBuffer *buf);
 static void DecodeStandbyOp(LogicalDecodingContext *ctx, XLogRecordBuffer *buf);
+static void DecodeLogicalMsgOp(LogicalDecodingContext *ctx, XLogRecordBuffer *buf);
 
 /* individual record(group)'s handlers */
 static void DecodeInsert(LogicalDecodingContext *ctx, XLogRecordBuffer *buf);
@@ -123,6 +125,10 @@ LogicalDecodingProcessRecord(LogicalDecodingContext *ctx, XLogReaderState *recor
 			DecodeHeapOp(ctx, &buf);
 			break;
 
+		case RM_LOGICALMSG_ID:
+			DecodeLogicalMsgOp(ctx, &buf);
+			break;
+
 			/*
 			 * Rmgrs irrelevant for logical decoding; they describe stuff not
 			 * represented in logical decoding. Add new rmgrs in rmgrlist.h's
@@ -457,6 +463,46 @@ DecodeHeapOp(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
 	}
 }
 
+/*
+ * Handle rmgr LOGICALMSG_ID records for DecodeRecordIntoReorderBuffer().
+ */
+static void
+DecodeLogicalMsgOp(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
+{
+	SnapBuild	   *builder = ctx->snapshot_builder;
+	XLogReaderState *r = buf->record;
+	TransactionId	xid = XLogRecGetXid(r);
+	uint8			info = XLogRecGetInfo(r) & ~XLR_INFO_MASK;
+	Snapshot		snapshot;
+	xl_logical_message *message;
+
+	if (info != XLOG_LOGICAL_MESSAGE)
+		elog(ERROR, "unexpected RM_LOGICALMSG_ID record type: %u", info);
+
+	ReorderBufferProcessXid(ctx->reorder, XLogRecGetXid(r), buf->origptr);
+
+	/* No point in doing anything yet. */
+	if (SnapBuildCurrentState(builder) < SNAPBUILD_FULL_SNAPSHOT)
+		return;
+
+	message = (xl_logical_message *) XLogRecGetData(r);
+
+	if (message->transactional &&
+		!SnapBuildProcessChange(builder, xid, buf->origptr))
+		return;
+	else if (!message->transactional &&
+			 (SnapBuildCurrentState(builder) != SNAPBUILD_CONSISTENT ||
+			  SnapBuildXactNeedsSkip(builder, buf->origptr)))
+		return;
+
+	snapshot = SnapBuildGetOrBuildSnapshot(builder, xid);
+	ReorderBufferQueueMessage(ctx->reorder, xid, snapshot, buf->endptr,
+							  message->transactional,
+							  message->message, /* first part of message is prefix */
+							  message->message_size,
+							  message->message + message->prefix_size);
+}
+
 static inline bool
 FilterByOrigin(LogicalDecodingContext *ctx, RepOriginId origin_id)
 {
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index 2e6d3f9..c06b2fa 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -62,6 +62,9 @@ static void commit_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
 				  XLogRecPtr commit_lsn);
 static void change_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
 				  Relation relation, ReorderBufferChange *change);
+static void message_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
+				  XLogRecPtr message_lsn, bool transactional,
+				  const char *prefix, Size message_size, const char *message);
 
 static void LoadOutputPlugin(OutputPluginCallbacks *callbacks, char *plugin);
 
@@ -178,6 +181,7 @@ StartupDecodingContext(List *output_plugin_options,
 	ctx->reorder->begin = begin_cb_wrapper;
 	ctx->reorder->apply_change = change_cb_wrapper;
 	ctx->reorder->commit = commit_cb_wrapper;
+	ctx->reorder->message = message_cb_wrapper;
 
 	ctx->out = makeStringInfo();
 	ctx->prepare_write = prepare_write;
@@ -702,6 +706,40 @@ filter_by_origin_cb_wrapper(LogicalDecodingContext *ctx, RepOriginId origin_id)
 	return ret;
 }
 
+static void
+message_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
+				   XLogRecPtr message_lsn, bool transactional,
+				   const char *prefix, Size message_size, const char *message)
+{
+	LogicalDecodingContext *ctx = cache->private_data;
+	LogicalErrorCallbackState state;
+	ErrorContextCallback errcallback;
+
+	if (ctx->callbacks.message_cb == NULL)
+		return;
+
+	/* Push callback + info on the error context stack */
+	state.ctx = ctx;
+	state.callback_name = "message";
+	state.report_location = message_lsn;
+	errcallback.callback = output_plugin_error_callback;
+	errcallback.arg = (void *) &state;
+	errcallback.previous = error_context_stack;
+	error_context_stack = &errcallback;
+
+	/* set output state */
+	ctx->accept_writes = true;
+	ctx->write_xid = txn != NULL ? txn->xid : InvalidTransactionId;
+	ctx->write_location = message_lsn;
+
+	/* do the actual work: call callback */
+	ctx->callbacks.message_cb(ctx, txn, message_lsn, transactional, prefix,
+							  message_size, message);
+
+	/* Pop the error context stack */
+	error_context_stack = errcallback.previous;
+}
+
 /*
  * Set the required catalog xmin horizon for historic snapshots in the current
  * replication slot.
diff --git a/src/backend/replication/logical/logicalfuncs.c b/src/backend/replication/logical/logicalfuncs.c
index f789fc1..552dac3 100644
--- a/src/backend/replication/logical/logicalfuncs.c
+++ b/src/backend/replication/logical/logicalfuncs.c
@@ -24,6 +24,8 @@
 #include "access/xlog_internal.h"
 #include "access/xlogutils.h"
 
+#include "access/xact.h"
+
 #include "catalog/pg_type.h"
 
 #include "nodes/makefuncs.h"
@@ -41,6 +43,7 @@
 #include "replication/decode.h"
 #include "replication/logical.h"
 #include "replication/logicalfuncs.h"
+#include "replication/message.h"
 
 #include "storage/fd.h"
 
@@ -363,3 +366,27 @@ pg_logical_slot_peek_binary_changes(PG_FUNCTION_ARGS)
 {
 	return pg_logical_slot_get_changes_guts(fcinfo, false, true);
 }
+
+
+/*
+ * SQL function for writing logical decding message into WAL.
+ */
+Datum
+pg_logical_emit_message_bytea(PG_FUNCTION_ARGS)
+{
+	bool		transactional = PG_GETARG_BOOL(0);
+	char	   *prefix = text_to_cstring(PG_GETARG_TEXT_PP(1));
+	bytea	   *data = PG_GETARG_BYTEA_PP(2);
+	XLogRecPtr	lsn;
+
+	lsn = LogLogicalMessage(prefix, VARDATA_ANY(data), VARSIZE_ANY_EXHDR(data),
+							transactional);
+	PG_RETURN_LSN(lsn);
+}
+
+Datum
+pg_logical_emit_message_text(PG_FUNCTION_ARGS)
+{
+	/* bytea and text are compatible */
+	return pg_logical_emit_message_bytea(fcinfo);
+}
diff --git a/src/backend/replication/logical/message.c b/src/backend/replication/logical/message.c
new file mode 100644
index 0000000..85c597b
--- /dev/null
+++ b/src/backend/replication/logical/message.c
@@ -0,0 +1,85 @@
+/*-------------------------------------------------------------------------
+ *
+ * message.c
+ *	  Generic logical messages.
+ *
+ * Copyright (c) 2013-2016, PostgreSQL Global Development Group
+ *
+ * IDENTIFICATION
+ *	  src/backend/replication/logical/message.c
+ *
+ * NOTES
+ *
+ * Generic logical messages allow XLOG logging of arbitrary binary blobs that
+ * get passed to the logical decoding plugin. In normal XLOG processing they
+ * are same as NOOP.
+ *
+ * These messages can be either transactional or non-transactional.
+ * Transactional messages are part of current transaction and will be sent to
+ * decoding plugin using in a same way as DML operations.
+ * Non-transactional messages are sent to the plugin at the time when the
+ * logical decoding reads them from XLOG.
+ *
+ * Every message carries prefix to avoid conflicts between different decoding
+ * plugins. The plugin authors must take extra care to use unique prefix,
+ * good options seems to be for example to use the name of the extension.
+ *
+ * ---------------------------------------------------------------------------
+ */
+
+#include "postgres.h"
+
+#include "access/xact.h"
+
+#include "catalog/indexing.h"
+
+#include "nodes/execnodes.h"
+
+#include "replication/message.h"
+#include "replication/logical.h"
+
+#include "utils/memutils.h"
+
+/*
+ * Write logical decoding message into XLog.
+ */
+XLogRecPtr
+LogLogicalMessage(const char *prefix, const char *message, size_t size,
+				  bool transactional)
+{
+	xl_logical_message	xlrec;
+
+	/*
+	 * Force xid to be allocated if we're emitting a transactional message.
+	 */
+	if (transactional)
+	{
+		Assert(IsTransactionState());
+		GetCurrentTransactionId();
+	}
+
+	xlrec.transactional = transactional;
+	xlrec.prefix_size = strlen(prefix) + 1;
+	xlrec.message_size = size;
+
+	XLogBeginInsert();
+	XLogRegisterData((char *) &xlrec, SizeOfLogicalMessage);
+	XLogRegisterData((char *) prefix, xlrec.prefix_size);
+	XLogRegisterData((char *) message, size);
+
+	return XLogInsert(RM_LOGICALMSG_ID, XLOG_LOGICAL_MESSAGE);
+}
+
+/*
+ * Redo is basically just noop for logical decoding messages.
+ */
+void
+logicalmsg_redo(XLogReaderState *record)
+{
+	uint8		info = XLogRecGetInfo(record) & ~XLR_INFO_MASK;
+
+	if (info != XLOG_LOGICAL_MESSAGE)
+			elog(PANIC, "logicalmsg_redo: unknown op code %u", info);
+
+	/* This is only interesting for logical decoding, see decode.c. */
+}
diff --git a/src/backend/replication/logical/reorderbuffer.c b/src/backend/replication/logical/reorderbuffer.c
index f2b8f4b..1420ddd 100644
--- a/src/backend/replication/logical/reorderbuffer.c
+++ b/src/backend/replication/logical/reorderbuffer.c
@@ -414,6 +414,14 @@ ReorderBufferReturnChange(ReorderBuffer *rb, ReorderBufferChange *change)
 				change->data.tp.oldtuple = NULL;
 			}
 			break;
+		case REORDER_BUFFER_CHANGE_MESSAGE:
+			if (change->data.msg.prefix != NULL)
+				pfree(change->data.msg.prefix);
+			change->data.msg.prefix = NULL;
+			if (change->data.msg.message != NULL)
+				pfree(change->data.msg.message);
+			change->data.msg.message = NULL;
+			break;
 		case REORDER_BUFFER_CHANGE_INTERNAL_SNAPSHOT:
 			if (change->data.snapshot)
 			{
@@ -627,6 +635,61 @@ ReorderBufferQueueChange(ReorderBuffer *rb, TransactionId xid, XLogRecPtr lsn,
 	ReorderBufferCheckSerializeTXN(rb, txn);
 }
 
+/*
+ * Queue message into a transaction so it can be processed upon commit.
+ */
+void
+ReorderBufferQueueMessage(ReorderBuffer *rb, TransactionId xid,
+						  Snapshot snapshot, XLogRecPtr lsn,
+						  bool transactional, const char *prefix,
+						  Size message_size, const char *message)
+{
+	if (transactional)
+	{
+		MemoryContext oldcontext;
+		ReorderBufferChange *change;
+
+		Assert(xid != InvalidTransactionId);
+
+		oldcontext = MemoryContextSwitchTo(rb->context);
+
+		change = ReorderBufferGetChange(rb);
+		change->action = REORDER_BUFFER_CHANGE_MESSAGE;
+		change->data.msg.prefix = pstrdup(prefix);
+		change->data.msg.message_size = message_size;
+		change->data.msg.message = palloc(message_size);
+		memcpy(change->data.msg.message, message, message_size);
+
+		ReorderBufferQueueChange(rb, xid, lsn, change);
+
+		MemoryContextSwitchTo(oldcontext);
+	}
+	else
+	{
+		ReorderBufferTXN   *txn = NULL;
+		volatile Snapshot	snapshot_now = snapshot;
+
+		if (xid != InvalidTransactionId)
+			txn = ReorderBufferTXNByXid(rb, xid, true, NULL, lsn, true);
+
+		/* setup snapshot to allow catalog access */
+		SetupHistoricSnapshot(snapshot_now, NULL);
+		PG_TRY();
+		{
+			rb->message(rb, txn, lsn, false, prefix, message_size, message);
+
+			TeardownHistoricSnapshot(false);
+		}
+		PG_CATCH();
+		{
+			TeardownHistoricSnapshot(true);
+			PG_RE_THROW();
+		}
+		PG_END_TRY();
+	}
+}
+
+
 static void
 AssertTXNLsnOrder(ReorderBuffer *rb)
 {
@@ -1493,6 +1556,13 @@ ReorderBufferCommit(ReorderBuffer *rb, TransactionId xid,
 					specinsert = change;
 					break;
 
+				case REORDER_BUFFER_CHANGE_MESSAGE:
+					rb->message(rb, txn, change->lsn, true,
+								change->data.msg.prefix,
+								change->data.msg.message_size,
+								change->data.msg.message);
+					break;
+
 				case REORDER_BUFFER_CHANGE_INTERNAL_SNAPSHOT:
 					/* get rid of the old */
 					TeardownHistoricSnapshot(false);
@@ -2159,6 +2229,33 @@ ReorderBufferSerializeChange(ReorderBuffer *rb, ReorderBufferTXN *txn,
 				}
 				break;
 			}
+		case REORDER_BUFFER_CHANGE_MESSAGE:
+			{
+				char	   *data;
+				Size		prefix_size = strlen(change->data.msg.prefix) + 1;
+
+				sz += prefix_size + change->data.msg.message_size +
+					sizeof(Size) + sizeof(Size);
+				ReorderBufferSerializeReserve(rb, sz);
+
+				data = ((char *) rb->outbuf) + sizeof(ReorderBufferDiskChange);
+
+				/* write the prefix including the size */
+				memcpy(data, &prefix_size, sizeof(Size));
+				data += sizeof(Size);
+				memcpy(data, change->data.msg.prefix,
+					   prefix_size);
+				data += prefix_size;
+
+				/* write the message including the size */
+				memcpy(data, &change->data.msg.message_size, sizeof(Size));
+				data += sizeof(Size);
+				memcpy(data, change->data.msg.message,
+					   change->data.msg.message_size);
+				data += change->data.msg.message_size;
+
+				break;
+			}
 		case REORDER_BUFFER_CHANGE_INTERNAL_SNAPSHOT:
 			{
 				Snapshot	snap;
@@ -2415,6 +2512,30 @@ ReorderBufferRestoreChange(ReorderBuffer *rb, ReorderBufferTXN *txn,
 			}
 
 			break;
+		case REORDER_BUFFER_CHANGE_MESSAGE:
+			{
+				Size		prefix_size;
+
+				/* read prefix */
+				memcpy(&prefix_size, data, sizeof(Size));
+				data += sizeof(Size);
+				change->data.msg.prefix = MemoryContextAlloc(rb->context,
+															 prefix_size);
+				memcpy(change->data.msg.prefix, data, prefix_size);
+				Assert(change->data.msg.prefix[prefix_size-1] == '\0');
+				data += prefix_size;
+
+				/* read the messsage */
+				memcpy(&change->data.msg.message_size, data, sizeof(Size));
+				data += sizeof(Size);
+				change->data.msg.message = MemoryContextAlloc(rb->context,
+												change->data.msg.message_size);
+				memcpy(change->data.msg.message, data,
+					   change->data.msg.message_size);
+				data += change->data.msg.message_size;
+
+				break;
+			}
 		case REORDER_BUFFER_CHANGE_INTERNAL_SNAPSHOT:
 			{
 				Snapshot	oldsnap;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index 179b85a..b4dc617 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -605,6 +605,25 @@ SnapBuildExportSnapshot(SnapBuild *builder)
 }
 
 /*
+ * Ensure there is a snapshot and if not build one for current transaction.
+ */
+Snapshot
+SnapBuildGetOrBuildSnapshot(SnapBuild *builder, TransactionId xid)
+{
+	Assert(builder->state == SNAPBUILD_CONSISTENT);
+
+	/* only build a new snapshot if we don't have a prebuilt one */
+	if (builder->snapshot == NULL)
+	{
+		builder->snapshot = SnapBuildBuildSnapshot(builder, xid);
+		/* inrease refcount for the snapshot builder */
+		SnapBuildSnapIncRefcount(builder->snapshot);
+	}
+
+	return builder->snapshot;
+}
+
+/*
  * Reset a previously SnapBuildExportSnapshot()'ed snapshot if there is
  * any. Aborts the previously started transaction and resets the resource
  * owner back to its original value.
diff --git a/src/bin/pg_xlogdump/.gitignore b/src/bin/pg_xlogdump/.gitignore
index eebaf30..c4783f1 100644
--- a/src/bin/pg_xlogdump/.gitignore
+++ b/src/bin/pg_xlogdump/.gitignore
@@ -1,22 +1,4 @@
 /pg_xlogdump
 # Source files copied from src/backend/access/rmgrdesc/
-/brindesc.c
-/clogdesc.c
-/committsdesc.c
-/dbasedesc.c
-/gindesc.c
-/gistdesc.c
-/hashdesc.c
-/heapdesc.c
-/mxactdesc.c
-/nbtdesc.c
-/relmapdesc.c
-/replorigindesc.c
-/seqdesc.c
-/smgrdesc.c
-/spgdesc.c
-/standbydesc.c
-/tblspcdesc.c
-/xactdesc.c
-/xlogdesc.c
+/*desc.c
 /xlogreader.c
diff --git a/src/bin/pg_xlogdump/rmgrdesc.c b/src/bin/pg_xlogdump/rmgrdesc.c
index f9cd395..6ba7f22 100644
--- a/src/bin/pg_xlogdump/rmgrdesc.c
+++ b/src/bin/pg_xlogdump/rmgrdesc.c
@@ -25,6 +25,7 @@
 #include "commands/dbcommands_xlog.h"
 #include "commands/sequence.h"
 #include "commands/tablespace.h"
+#include "replication/message.h"
 #include "replication/origin.h"
 #include "rmgrdesc.h"
 #include "storage/standbydefs.h"
diff --git a/src/include/access/rmgrlist.h b/src/include/access/rmgrlist.h
index fab912d..35c242d 100644
--- a/src/include/access/rmgrlist.h
+++ b/src/include/access/rmgrlist.h
@@ -45,3 +45,4 @@ PG_RMGR(RM_SPGIST_ID, "SPGist", spg_redo, spg_desc, spg_identify, spg_xlog_start
 PG_RMGR(RM_BRIN_ID, "BRIN", brin_redo, brin_desc, brin_identify, NULL, NULL)
 PG_RMGR(RM_COMMIT_TS_ID, "CommitTs", commit_ts_redo, commit_ts_desc, commit_ts_identify, NULL, NULL)
 PG_RMGR(RM_REPLORIGIN_ID, "ReplicationOrigin", replorigin_redo, replorigin_desc, replorigin_identify, NULL, NULL)
+PG_RMGR(RM_LOGICALMSG_ID, "LogicalMessage", logicalmsg_redo, logicalmsg_desc, logicalmsg_identify, NULL, NULL)
diff --git a/src/include/catalog/pg_proc.h b/src/include/catalog/pg_proc.h
index a595327..3713739 100644
--- a/src/include/catalog/pg_proc.h
+++ b/src/include/catalog/pg_proc.h
@@ -5114,6 +5114,10 @@ DATA(insert OID = 3784 (  pg_logical_slot_peek_changes PGNSP PGUID 12 1000 1000
 DESCR("peek at changes from replication slot");
 DATA(insert OID = 3785 (  pg_logical_slot_peek_binary_changes PGNSP PGUID 12 1000 1000 25 0 f f f f f t v u 4 0 2249 "19 3220 23 1009" "{19,3220,23,1009,3220,28,17}" "{i,i,i,v,o,o,o}" "{slot_name,upto_lsn,upto_nchanges,options,location,xid,data}" _null_ _null_ pg_logical_slot_peek_binary_changes _null_ _null_ _null_ ));
 DESCR("peek at binary changes from replication slot");
+DATA(insert OID = 3577 (  pg_logical_emit_message PGNSP PGUID 12 1 0 0 0 f f f f t f v u 3 0 3220 "16 25 25" _null_ _null_ _null_ _null_ _null_ pg_logical_emit_message_text _null_ _null_ _null_ ));
+DESCR("emit a textual logical decoding message");
+DATA(insert OID = 3578 (  pg_logical_emit_message PGNSP PGUID 12 1 0 0 0 f f f f t f v u 3 0 3220 "16 25 17" _null_ _null_ _null_ _null_ _null_ pg_logical_emit_message_bytea _null_ _null_ _null_ ));
+DESCR("emit a binary logical decoding message");
 
 /* event triggers */
 DATA(insert OID = 3566 (  pg_event_trigger_dropped_objects		PGNSP PGUID 12 10 100 0 0 f f f f t t s s 0 0 2249 "" "{26,26,23,16,16,16,25,25,25,25,1009,1009}" "{o,o,o,o,o,o,o,o,o,o,o,o}" "{classid, objid, objsubid, original, normal, is_temporary, object_type, schema_name, object_name, object_identity, address_names, address_args}" _null_ _null_ pg_event_trigger_dropped_objects _null_ _null_ _null_ ));
diff --git a/src/include/replication/logicalfuncs.h b/src/include/replication/logicalfuncs.h
index c87a1df..5540414 100644
--- a/src/include/replication/logicalfuncs.h
+++ b/src/include/replication/logicalfuncs.h
@@ -21,4 +21,6 @@ extern Datum pg_logical_slot_get_binary_changes(PG_FUNCTION_ARGS);
 extern Datum pg_logical_slot_peek_changes(PG_FUNCTION_ARGS);
 extern Datum pg_logical_slot_peek_binary_changes(PG_FUNCTION_ARGS);
 
+extern Datum pg_logical_emit_message_bytea(PG_FUNCTION_ARGS);
+extern Datum pg_logical_emit_message_text(PG_FUNCTION_ARGS);
 #endif
diff --git a/src/include/replication/message.h b/src/include/replication/message.h
new file mode 100644
index 0000000..8b968d5
--- /dev/null
+++ b/src/include/replication/message.h
@@ -0,0 +1,41 @@
+/*-------------------------------------------------------------------------
+ * message.h
+ *	   Exports from replication/logical/message.c
+ *
+ * Copyright (c) 2013-2016, PostgreSQL Global Development Group
+ *
+ * src/include/replication/message.h
+ *-------------------------------------------------------------------------
+ */
+#ifndef PG_LOGICAL_MESSAGE_H
+#define PG_LOGICAL_MESSAGE_H
+
+#include "access/xlog.h"
+#include "access/xlogdefs.h"
+#include "access/xlogreader.h"
+
+/*
+ * Generic logical decoding message wal record.
+ */
+typedef struct xl_logical_message
+{
+	bool		transactional;					/* is message transactional? */
+	Size		prefix_size;					/* length of prefix */
+	Size		message_size;					/* size of the message */
+	char		message[FLEXIBLE_ARRAY_MEMBER];	/* message including the null
+												 * terminated prefix of length
+												 * prefix_size */
+} xl_logical_message;
+
+#define SizeOfLogicalMessage	(offsetof(xl_logical_message, message))
+
+extern XLogRecPtr LogLogicalMessage(const char *prefix, const char *message,
+									size_t size, bool transactional);
+
+/* RMGR API*/
+#define XLOG_LOGICAL_MESSAGE	0x00
+void		logicalmsg_redo(XLogReaderState *record);
+void		logicalmsg_desc(StringInfo buf, XLogReaderState *record);
+const char *logicalmsg_identify(uint8 info);
+
+#endif   /* PG_LOGICAL_MESSAGE_H */
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 577b12e..3a2ca98 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -74,6 +74,18 @@ typedef void (*LogicalDecodeCommitCB) (
 												   XLogRecPtr commit_lsn);
 
 /*
+ * Called for the generic logical decoding messages.
+ */
+typedef void (*LogicalDecodeMessageCB) (
+											 struct LogicalDecodingContext *,
+											 ReorderBufferTXN *txn,
+											 XLogRecPtr message_lsn,
+											 bool transactional,
+											 const char *prefix,
+											 Size message_size,
+											 const char *message);
+
+/*
  * Filter changes by origin.
  */
 typedef bool (*LogicalDecodeFilterByOriginCB) (
@@ -96,6 +108,7 @@ typedef struct OutputPluginCallbacks
 	LogicalDecodeBeginCB begin_cb;
 	LogicalDecodeChangeCB change_cb;
 	LogicalDecodeCommitCB commit_cb;
+	LogicalDecodeMessageCB message_cb;
 	LogicalDecodeFilterByOriginCB filter_by_origin_cb;
 	LogicalDecodeShutdownCB shutdown_cb;
 } OutputPluginCallbacks;
diff --git a/src/include/replication/reorderbuffer.h b/src/include/replication/reorderbuffer.h
index b52d06a..4c54953 100644
--- a/src/include/replication/reorderbuffer.h
+++ b/src/include/replication/reorderbuffer.h
@@ -54,6 +54,7 @@ enum ReorderBufferChangeType
 	REORDER_BUFFER_CHANGE_INSERT,
 	REORDER_BUFFER_CHANGE_UPDATE,
 	REORDER_BUFFER_CHANGE_DELETE,
+	REORDER_BUFFER_CHANGE_MESSAGE,
 	REORDER_BUFFER_CHANGE_INTERNAL_SNAPSHOT,
 	REORDER_BUFFER_CHANGE_INTERNAL_COMMAND_ID,
 	REORDER_BUFFER_CHANGE_INTERNAL_TUPLECID,
@@ -98,6 +99,14 @@ typedef struct ReorderBufferChange
 			ReorderBufferTupleBuf *newtuple;
 		}			tp;
 
+		/* Message with arbitrary data. */
+		struct
+		{
+			char   *prefix;
+			Size	message_size;
+			char   *message;
+		} msg;
+
 		/* New snapshot, set when action == *_INTERNAL_SNAPSHOT */
 		Snapshot	snapshot;
 
@@ -274,6 +283,15 @@ typedef void (*ReorderBufferCommitCB) (
 												   ReorderBufferTXN *txn,
 												   XLogRecPtr commit_lsn);
 
+/* message callback signature */
+typedef void (*ReorderBufferMessageCB) (
+												   ReorderBuffer *rb,
+												   ReorderBufferTXN *txn,
+												   XLogRecPtr message_lsn,
+												   bool transactional,
+												   const char *prefix, Size sz,
+												   const char *message);
+
 struct ReorderBuffer
 {
 	/*
@@ -300,6 +318,7 @@ struct ReorderBuffer
 	ReorderBufferBeginCB begin;
 	ReorderBufferApplyChangeCB apply_change;
 	ReorderBufferCommitCB commit;
+	ReorderBufferMessageCB message;
 
 	/*
 	 * Pointer that will be passed untouched to the callbacks.
@@ -350,6 +369,9 @@ ReorderBufferChange *ReorderBufferGetChange(ReorderBuffer *);
 void		ReorderBufferReturnChange(ReorderBuffer *, ReorderBufferChange *);
 
 void		ReorderBufferQueueChange(ReorderBuffer *, TransactionId, XLogRecPtr lsn, ReorderBufferChange *);
+void		ReorderBufferQueueMessage(ReorderBuffer *, TransactionId, Snapshot snapshot, XLogRecPtr lsn,
+									  bool transactional, const char *prefix,
+									  Size message_size, const char *message);
 void ReorderBufferCommit(ReorderBuffer *, TransactionId,
 					XLogRecPtr commit_lsn, XLogRecPtr end_lsn,
 	  TimestampTz commit_time, RepOriginId origin_id, XLogRecPtr origin_lsn);
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index 75955af..c4127a1 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -63,6 +63,8 @@ extern const char *SnapBuildExportSnapshot(SnapBuild *snapstate);
 extern void SnapBuildClearExportedSnapshot(void);
 
 extern SnapBuildState SnapBuildCurrentState(SnapBuild *snapstate);
+extern Snapshot SnapBuildGetOrBuildSnapshot(SnapBuild *builder,
+											TransactionId xid);
 
 extern bool SnapBuildXactNeedsSkip(SnapBuild *snapstate, XLogRecPtr ptr);
 
-- 
1.9.1

From b74e6dc5956446d514130c575263f4ba6ad71db3 Mon Sep 17 00:00:00 2001
From: Petr Jelinek <pjmodos@pjmodos.net>
Date: Wed, 24 Feb 2016 17:02:36 +0100
Subject: [PATCH] Logical Decoding Messages

---
 contrib/test_decoding/Makefile                  |   2 +-
 contrib/test_decoding/expected/ddl.out          |  21 ++--
 contrib/test_decoding/expected/messages.out     |  79 ++++++++++++++++
 contrib/test_decoding/sql/ddl.sql               |   3 +-
 contrib/test_decoding/sql/messages.sql          |  25 +++++
 contrib/test_decoding/test_decoding.c           |  18 ++++
 doc/src/sgml/func.sgml                          |  45 +++++++++
 doc/src/sgml/logicaldecoding.sgml               |  38 ++++++++
 src/backend/access/rmgrdesc/Makefile            |   6 +-
 src/backend/access/rmgrdesc/logicalmsgdesc.c    |  41 ++++++++
 src/backend/access/transam/rmgr.c               |   1 +
 src/backend/replication/logical/Makefile        |   2 +-
 src/backend/replication/logical/decode.c        |  46 +++++++++
 src/backend/replication/logical/logical.c       |  38 ++++++++
 src/backend/replication/logical/logicalfuncs.c  |  27 ++++++
 src/backend/replication/logical/message.c       |  87 +++++++++++++++++
 src/backend/replication/logical/reorderbuffer.c | 121 ++++++++++++++++++++++++
 src/backend/replication/logical/snapbuild.c     |  19 ++++
 src/bin/pg_xlogdump/.gitignore                  |  21 +---
 src/bin/pg_xlogdump/rmgrdesc.c                  |   1 +
 src/include/access/rmgrlist.h                   |   1 +
 src/include/catalog/pg_proc.h                   |   4 +
 src/include/replication/logicalfuncs.h          |   2 +
 src/include/replication/message.h               |  41 ++++++++
 src/include/replication/output_plugin.h         |  13 +++
 src/include/replication/reorderbuffer.h         |  22 +++++
 src/include/replication/snapbuild.h             |   2 +
 27 files changed, 693 insertions(+), 33 deletions(-)
 create mode 100644 contrib/test_decoding/expected/messages.out
 create mode 100644 contrib/test_decoding/sql/messages.sql
 create mode 100644 src/backend/access/rmgrdesc/logicalmsgdesc.c
 create mode 100644 src/backend/replication/logical/message.c
 create mode 100644 src/include/replication/message.h

diff --git a/contrib/test_decoding/Makefile b/contrib/test_decoding/Makefile
index 06c9546..309cb0b 100644
--- a/contrib/test_decoding/Makefile
+++ b/contrib/test_decoding/Makefile
@@ -38,7 +38,7 @@ submake-test_decoding:
 	$(MAKE) -C $(top_builddir)/contrib/test_decoding
 
 REGRESSCHECKS=ddl xact rewrite toast permissions decoding_in_xact \
-	decoding_into_rel binary prepared replorigin time
+	decoding_into_rel binary prepared replorigin time messages
 
 regresscheck: | submake-regress submake-test_decoding temp-install
 	$(MKDIR_P) regression_output
diff --git a/contrib/test_decoding/expected/ddl.out b/contrib/test_decoding/expected/ddl.out
index 77719e8..32cd24d 100644
--- a/contrib/test_decoding/expected/ddl.out
+++ b/contrib/test_decoding/expected/ddl.out
@@ -220,11 +220,17 @@ SELECT data FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'inc
 (7 rows)
 
 /*
- * check that disk spooling works
+ * check that disk spooling works (also for logical messages)
  */
 BEGIN;
 CREATE TABLE tr_etoomuch (id serial primary key, data int);
 INSERT INTO tr_etoomuch(data) SELECT g.i FROM generate_series(1, 10234) g(i);
+SELECT 'tx logical msg' FROM pg_logical_emit_message(true, 'test', 'tx logical msg');
+    ?column?    
+----------------
+ tx logical msg
+(1 row)
+
 DELETE FROM tr_etoomuch WHERE id < 5000;
 UPDATE tr_etoomuch SET data = - data WHERE id > 5000;
 COMMIT;
@@ -233,12 +239,13 @@ SELECT count(*), min(data), max(data)
 FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'include-xids', '0', 'skip-empty-xacts', '1')
 GROUP BY substring(data, 1, 24)
 ORDER BY 1,2;
- count |                       min                       |                                  max                                   
--------+-------------------------------------------------+------------------------------------------------------------------------
-     1 | BEGIN                                           | BEGIN
-     1 | COMMIT                                          | COMMIT
- 20467 | table public.tr_etoomuch: DELETE: id[integer]:1 | table public.tr_etoomuch: UPDATE: id[integer]:9999 data[integer]:-9999
-(3 rows)
+ count |                                  min                                  |                                  max                                   
+-------+-----------------------------------------------------------------------+------------------------------------------------------------------------
+     1 | BEGIN                                                                 | BEGIN
+     1 | COMMIT                                                                | COMMIT
+     1 | message: transactional: 1 prefix: test, sz: 14 content:tx logical msg | message: transactional: 1 prefix: test, sz: 14 content:tx logical msg
+ 20467 | table public.tr_etoomuch: DELETE: id[integer]:1                       | table public.tr_etoomuch: UPDATE: id[integer]:9999 data[integer]:-9999
+(4 rows)
 
 -- check updates of primary keys work correctly
 BEGIN;
diff --git a/contrib/test_decoding/expected/messages.out b/contrib/test_decoding/expected/messages.out
new file mode 100644
index 0000000..e26f793
--- /dev/null
+++ b/contrib/test_decoding/expected/messages.out
@@ -0,0 +1,79 @@
+-- predictability
+SET synchronous_commit = on;
+SET client_encoding = 'utf8';
+SELECT 'init' FROM pg_create_logical_replication_slot('regression_slot', 'test_decoding');
+ ?column? 
+----------
+ init
+(1 row)
+
+SELECT 'msg1' FROM pg_logical_emit_message(true, 'test', 'msg1');
+ ?column? 
+----------
+ msg1
+(1 row)
+
+SELECT 'msg2' FROM pg_logical_emit_message(false, 'test', 'msg2');
+ ?column? 
+----------
+ msg2
+(1 row)
+
+BEGIN;
+SELECT 'msg3' FROM pg_logical_emit_message(true, 'test', 'msg3');
+ ?column? 
+----------
+ msg3
+(1 row)
+
+SELECT 'msg4' FROM pg_logical_emit_message(false, 'test', 'msg4');
+ ?column? 
+----------
+ msg4
+(1 row)
+
+ROLLBACK;
+BEGIN;
+SELECT 'msg5' FROM pg_logical_emit_message(true, 'test', 'msg5');
+ ?column? 
+----------
+ msg5
+(1 row)
+
+SELECT 'msg6' FROM pg_logical_emit_message(false, 'test', 'msg6');
+ ?column? 
+----------
+ msg6
+(1 row)
+
+SELECT 'msg7' FROM pg_logical_emit_message(true, 'test', 'msg7');
+ ?column? 
+----------
+ msg7
+(1 row)
+
+COMMIT;
+SELECT 'žluťoučký kůň' FROM pg_logical_emit_message(true, 'test', 'žluťoučký kůň');
+   ?column?    
+---------------
+ žluťoučký kůň
+(1 row)
+
+SELECT data FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'force-binary', '0', 'skip-empty-xacts', '1');
+                                 data                                 
+----------------------------------------------------------------------
+ message: transactional: 1 prefix: test, sz: 4 content:msg1
+ message: transactional: 0 prefix: test, sz: 4 content:msg2
+ message: transactional: 0 prefix: test, sz: 4 content:msg4
+ message: transactional: 0 prefix: test, sz: 4 content:msg6
+ message: transactional: 1 prefix: test, sz: 4 content:msg5
+ message: transactional: 1 prefix: test, sz: 4 content:msg7
+ message: transactional: 1 prefix: test, sz: 19 content:žluťoučký kůň
+(7 rows)
+
+SELECT 'init' FROM pg_drop_replication_slot('regression_slot');
+ ?column? 
+----------
+ init
+(1 row)
+
diff --git a/contrib/test_decoding/sql/ddl.sql b/contrib/test_decoding/sql/ddl.sql
index ad928ad..b1f7bf6 100644
--- a/contrib/test_decoding/sql/ddl.sql
+++ b/contrib/test_decoding/sql/ddl.sql
@@ -108,11 +108,12 @@ DELETE FROM tr_pkey;
 SELECT data FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'include-xids', '0', 'skip-empty-xacts', '1');
 
 /*
- * check that disk spooling works
+ * check that disk spooling works (also for logical messages)
  */
 BEGIN;
 CREATE TABLE tr_etoomuch (id serial primary key, data int);
 INSERT INTO tr_etoomuch(data) SELECT g.i FROM generate_series(1, 10234) g(i);
+SELECT 'tx logical msg' FROM pg_logical_emit_message(true, 'test', 'tx logical msg');
 DELETE FROM tr_etoomuch WHERE id < 5000;
 UPDATE tr_etoomuch SET data = - data WHERE id > 5000;
 COMMIT;
diff --git a/contrib/test_decoding/sql/messages.sql b/contrib/test_decoding/sql/messages.sql
new file mode 100644
index 0000000..d72191b
--- /dev/null
+++ b/contrib/test_decoding/sql/messages.sql
@@ -0,0 +1,25 @@
+-- predictability
+SET synchronous_commit = on;
+SET client_encoding = 'utf8';
+
+SELECT 'init' FROM pg_create_logical_replication_slot('regression_slot', 'test_decoding');
+
+SELECT 'msg1' FROM pg_logical_emit_message(true, 'test', 'msg1');
+SELECT 'msg2' FROM pg_logical_emit_message(false, 'test', 'msg2');
+
+BEGIN;
+SELECT 'msg3' FROM pg_logical_emit_message(true, 'test', 'msg3');
+SELECT 'msg4' FROM pg_logical_emit_message(false, 'test', 'msg4');
+ROLLBACK;
+
+BEGIN;
+SELECT 'msg5' FROM pg_logical_emit_message(true, 'test', 'msg5');
+SELECT 'msg6' FROM pg_logical_emit_message(false, 'test', 'msg6');
+SELECT 'msg7' FROM pg_logical_emit_message(true, 'test', 'msg7');
+COMMIT;
+
+SELECT 'žluťoučký kůň' FROM pg_logical_emit_message(true, 'test', 'žluťoučký kůň');
+
+SELECT data FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'force-binary', '0', 'skip-empty-xacts', '1');
+
+SELECT 'init' FROM pg_drop_replication_slot('regression_slot');
diff --git a/contrib/test_decoding/test_decoding.c b/contrib/test_decoding/test_decoding.c
index 4cf808f..3336e1e 100644
--- a/contrib/test_decoding/test_decoding.c
+++ b/contrib/test_decoding/test_decoding.c
@@ -21,6 +21,7 @@
 
 #include "replication/output_plugin.h"
 #include "replication/logical.h"
+#include "replication/message.h"
 #include "replication/origin.h"
 
 #include "utils/builtins.h"
@@ -63,6 +64,10 @@ static void pg_decode_change(LogicalDecodingContext *ctx,
 				 ReorderBufferChange *change);
 static bool pg_decode_filter(LogicalDecodingContext *ctx,
 				 RepOriginId origin_id);
+static void pg_decode_message(LogicalDecodingContext *ctx,
+							  ReorderBufferTXN *txn, XLogRecPtr message_lsn,
+							  bool transactional, const char *prefix,
+							  Size sz, const char *message);
 
 void
 _PG_init(void)
@@ -82,6 +87,7 @@ _PG_output_plugin_init(OutputPluginCallbacks *cb)
 	cb->commit_cb = pg_decode_commit_txn;
 	cb->filter_by_origin_cb = pg_decode_filter;
 	cb->shutdown_cb = pg_decode_shutdown;
+	cb->message_cb = pg_decode_message;
 }
 
 
@@ -471,3 +477,15 @@ pg_decode_change(LogicalDecodingContext *ctx, ReorderBufferTXN *txn,
 
 	OutputPluginWrite(ctx, true);
 }
+
+static void
+pg_decode_message(LogicalDecodingContext *ctx,
+				  ReorderBufferTXN *txn, XLogRecPtr lsn, bool transactional,
+				  const char *prefix, Size sz, const char *message)
+{
+	OutputPluginPrepareWrite(ctx, true);
+	appendStringInfo(ctx->out, "message: transactional: %d prefix: %s, sz: %zu content:",
+					 transactional, prefix, sz);
+	appendBinaryStringInfo(ctx->out, message, sz);
+	OutputPluginWrite(ctx, true);
+}
diff --git a/doc/src/sgml/func.sgml b/doc/src/sgml/func.sgml
index 1bc9fbc..14b686f 100644
--- a/doc/src/sgml/func.sgml
+++ b/doc/src/sgml/func.sgml
@@ -18237,6 +18237,51 @@ postgres=# SELECT * FROM pg_xlogfile_name_offset(pg_stop_backup());
        </entry>
       </row>
 
+      <row>
+       <entry id="pg-logical-emit-message-text">
+        <indexterm>
+         <primary>pg_logical_emit_message</primary>
+        </indexterm>
+        <literal><function>pg_logical_emit_message(<parameter>transactional</parameter> <type>bool</type>, <parameter>prefix</parameter> <type>text</type>, <parameter>content</parameter> <type>text</type>)</function></literal>
+       </entry>
+       <entry>
+        void
+       </entry>
+       <entry>
+        Emit text logical decoding message. This can be used to pass generic
+        messages to logical decoding plugins through WAL. The parameter
+        <parameter>transactional</parameter> specifies if the message should
+        be part of current transaction or if it should be written immediately
+        and decoded as soon as the logical decoding reads the record. The
+        <parameter>prefix</parameter> is textual prefix used by the logical
+        decoding plugins to easily recognize interesting messages for them.
+        The <parameter>content</parameter> is the text of the message.
+       </entry>
+      </row>
+
+      <row>
+       <entry id="pg-logical-emit-message-bytea">
+        <indexterm>
+         <primary>>pg_logical_emit_message</primary>
+        </indexterm>
+        <literal><function>>pg_logical_emit_message(<parameter>transactional</parameter> <type>bool</type>, <parameter>prefix</parameter> <type>text</type>, <parameter>content</parameter> <type>bytea</type>)</function></literal>
+       </entry>
+       <entry>
+        void
+       </entry>
+       <entry>
+        Emit binary logical decoding message. This can be used to pass generic
+        messages to logical decoding plugins through WAL. The parameter
+        <parameter>transactional</parameter> specifies if the message should
+        be part of current transaction or if it should be written immediately
+        and decoded as soon as the logical decoding reads the record. The
+        <parameter>prefix</parameter> is textual prefix used by the logical
+        decoding plugins to easily recognize interesting messages for them.
+        The <parameter>content</parameter> is the binary content of the
+        message.
+       </entry>
+      </row>
+
      </tbody>
     </tgroup>
    </table>
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml
index 45fdfeb..8306d9f 100644
--- a/doc/src/sgml/logicaldecoding.sgml
+++ b/doc/src/sgml/logicaldecoding.sgml
@@ -363,6 +363,7 @@ typedef struct OutputPluginCallbacks
     LogicalDecodeBeginCB begin_cb;
     LogicalDecodeChangeCB change_cb;
     LogicalDecodeCommitCB commit_cb;
+    LogicalDecodeMessageCB message_cb;
     LogicalDecodeFilterByOriginCB filter_by_origin_cb;
     LogicalDecodeShutdownCB shutdown_cb;
 } OutputPluginCallbacks;
@@ -602,6 +603,43 @@ typedef bool (*LogicalDecodeFilterByOriginCB) (
        more efficient.
      </para>
      </sect3>
+
+    <sect3 id="logicaldecoding-output-plugin-message">
+     <title>Generic Message Callback</title>
+
+     <para>
+      The optional <function>message_cb</function> callback is called whenever
+      a logical decoding message has been decoded.
+<programlisting>
+typedef void (*LogicalDecodeMessageCB) (
+    struct LogicalDecodingContext *,
+    ReorderBufferTXN *txn,
+    XLogRecPtr message_lsn,
+    bool transactional,
+    const char *prefix,
+    Size message_size,
+    const char *message
+);
+</programlisting>
+      The <parameter>txn</parameter> parameter contains meta information about
+      the transaction, like the time stamp at which it has been committed and
+      its XID. Note however that it can be NULL when the message is
+      non-transactional and the XID was not assigned yet in the transaction
+      which logged the message. The <parameter>lsn</parameter> has WAL
+      position of the message. The <parameter>transactional</parameter> says
+      if the message was sent as transactional or not.
+      The <parameter>prefix</parameter> is arbitrary null-terminated prefix
+      which can be used for identifying interesting messages for the current
+      plugin. And finally the <parameter>message</parameter> parameter holds
+      the actual message of <parameter>message_size</parameter> size.
+     </para>
+     <para>
+      Extra care should be taken to ensure that the prefix the output plugin
+      considers interesting is unique. Using name of the extension or the
+      output plugin itself is often a good choice.
+     </para>
+    </sect3>
+
    </sect2>
 
    <sect2 id="logicaldecoding-output-plugin-output">
diff --git a/src/backend/access/rmgrdesc/Makefile b/src/backend/access/rmgrdesc/Makefile
index c0e38fd..5514db1 100644
--- a/src/backend/access/rmgrdesc/Makefile
+++ b/src/backend/access/rmgrdesc/Makefile
@@ -9,8 +9,8 @@ top_builddir = ../../../..
 include $(top_builddir)/src/Makefile.global
 
 OBJS = brindesc.o clogdesc.o committsdesc.o dbasedesc.o genericdesc.o \
-	   gindesc.o gistdesc.o hashdesc.o heapdesc.o mxactdesc.o nbtdesc.o \
-	   relmapdesc.o replorigindesc.o seqdesc.o smgrdesc.o spgdesc.o \
-	   standbydesc.o tblspcdesc.o xactdesc.o xlogdesc.o
+	   gindesc.o gistdesc.o hashdesc.o heapdesc.o logicalmsgdesc.o \
+	   mxactdesc.o nbtdesc.o relmapdesc.o replorigindesc.o seqdesc.o \
+	   smgrdesc.o spgdesc.o standbydesc.o tblspcdesc.o xactdesc.o xlogdesc.o
 
 include $(top_srcdir)/src/backend/common.mk
diff --git a/src/backend/access/rmgrdesc/logicalmsgdesc.c b/src/backend/access/rmgrdesc/logicalmsgdesc.c
new file mode 100644
index 0000000..b194e14
--- /dev/null
+++ b/src/backend/access/rmgrdesc/logicalmsgdesc.c
@@ -0,0 +1,41 @@
+/*-------------------------------------------------------------------------
+ *
+ * logicalmsgdesc.c
+ *	  rmgr descriptor routines for replication/logical/message.c
+ *
+ * Portions Copyright (c) 2015-2016, PostgreSQL Global Development Group
+ *
+ *
+ * IDENTIFICATION
+ *	  src/backend/access/rmgrdesc/logicalmsgdesc.c
+ *
+ *-------------------------------------------------------------------------
+ */
+#include "postgres.h"
+
+#include "replication/message.h"
+
+void
+logicalmsg_desc(StringInfo buf, XLogReaderState *record)
+{
+	char	   *rec = XLogRecGetData(record);
+	uint8		info = XLogRecGetInfo(record) & ~XLR_INFO_MASK;
+
+	if (info == XLOG_LOGICAL_MESSAGE)
+	{
+		xl_logical_message *xlrec = (xl_logical_message *) rec;
+
+		appendStringInfo(buf, "%s message size %zu bytes",
+				   xlrec->transactional ? "transactional" : "nontransactional",
+						 xlrec->message_size);
+	}
+}
+
+const char *
+logicalmsg_identify(uint8 info)
+{
+	if ((info & ~XLR_INFO_MASK) == XLOG_LOGICAL_MESSAGE)
+		return "MESSAGE";
+
+	return NULL;
+}
diff --git a/src/backend/access/transam/rmgr.c b/src/backend/access/transam/rmgr.c
index 7b38c16..31c5fd1 100644
--- a/src/backend/access/transam/rmgr.c
+++ b/src/backend/access/transam/rmgr.c
@@ -24,6 +24,7 @@
 #include "commands/dbcommands_xlog.h"
 #include "commands/sequence.h"
 #include "commands/tablespace.h"
+#include "replication/message.h"
 #include "replication/origin.h"
 #include "storage/standby.h"
 #include "utils/relmapper.h"
diff --git a/src/backend/replication/logical/Makefile b/src/backend/replication/logical/Makefile
index 8adea13..1d7ca06 100644
--- a/src/backend/replication/logical/Makefile
+++ b/src/backend/replication/logical/Makefile
@@ -14,7 +14,7 @@ include $(top_builddir)/src/Makefile.global
 
 override CPPFLAGS := -I$(srcdir) $(CPPFLAGS)
 
-OBJS = decode.o logical.o logicalfuncs.o reorderbuffer.o origin.o \
+OBJS = decode.o logical.o logicalfuncs.o message.o origin.o reorderbuffer.o \
 	snapbuild.o
 
 include $(top_srcdir)/src/backend/common.mk
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index 7781ebc..3e80c4a 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -39,6 +39,7 @@
 
 #include "replication/decode.h"
 #include "replication/logical.h"
+#include "replication/message.h"
 #include "replication/reorderbuffer.h"
 #include "replication/origin.h"
 #include "replication/snapbuild.h"
@@ -58,6 +59,7 @@ static void DecodeHeapOp(LogicalDecodingContext *ctx, XLogRecordBuffer *buf);
 static void DecodeHeap2Op(LogicalDecodingContext *ctx, XLogRecordBuffer *buf);
 static void DecodeXactOp(LogicalDecodingContext *ctx, XLogRecordBuffer *buf);
 static void DecodeStandbyOp(LogicalDecodingContext *ctx, XLogRecordBuffer *buf);
+static void DecodeLogicalMsgOp(LogicalDecodingContext *ctx, XLogRecordBuffer *buf);
 
 /* individual record(group)'s handlers */
 static void DecodeInsert(LogicalDecodingContext *ctx, XLogRecordBuffer *buf);
@@ -123,6 +125,10 @@ LogicalDecodingProcessRecord(LogicalDecodingContext *ctx, XLogReaderState *recor
 			DecodeHeapOp(ctx, &buf);
 			break;
 
+		case RM_LOGICALMSG_ID:
+			DecodeLogicalMsgOp(ctx, &buf);
+			break;
+
 			/*
 			 * Rmgrs irrelevant for logical decoding; they describe stuff not
 			 * represented in logical decoding. Add new rmgrs in rmgrlist.h's
@@ -458,6 +464,46 @@ DecodeHeapOp(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
 	}
 }
 
+/*
+ * Handle rmgr LOGICALMSG_ID records for DecodeRecordIntoReorderBuffer().
+ */
+static void
+DecodeLogicalMsgOp(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
+{
+	SnapBuild	   *builder = ctx->snapshot_builder;
+	XLogReaderState *r = buf->record;
+	TransactionId	xid = XLogRecGetXid(r);
+	uint8			info = XLogRecGetInfo(r) & ~XLR_INFO_MASK;
+	Snapshot		snapshot;
+	xl_logical_message *message;
+
+	if (info != XLOG_LOGICAL_MESSAGE)
+		elog(ERROR, "unexpected RM_LOGICALMSG_ID record type: %u", info);
+
+	ReorderBufferProcessXid(ctx->reorder, XLogRecGetXid(r), buf->origptr);
+
+	/* No point in doing anything yet. */
+	if (SnapBuildCurrentState(builder) < SNAPBUILD_FULL_SNAPSHOT)
+		return;
+
+	message = (xl_logical_message *) XLogRecGetData(r);
+
+	if (message->transactional &&
+		!SnapBuildProcessChange(builder, xid, buf->origptr))
+		return;
+	else if (!message->transactional &&
+			 (SnapBuildCurrentState(builder) != SNAPBUILD_CONSISTENT ||
+			  SnapBuildXactNeedsSkip(builder, buf->origptr)))
+		return;
+
+	snapshot = SnapBuildGetOrBuildSnapshot(builder, xid);
+	ReorderBufferQueueMessage(ctx->reorder, xid, snapshot, buf->endptr,
+							  message->transactional,
+							  message->message, /* first part of message is prefix */
+							  message->message_size,
+							  message->message + message->prefix_size);
+}
+
 static inline bool
 FilterByOrigin(LogicalDecodingContext *ctx, RepOriginId origin_id)
 {
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index 2e6d3f9..c06b2fa 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -62,6 +62,9 @@ static void commit_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
 				  XLogRecPtr commit_lsn);
 static void change_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
 				  Relation relation, ReorderBufferChange *change);
+static void message_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
+				  XLogRecPtr message_lsn, bool transactional,
+				  const char *prefix, Size message_size, const char *message);
 
 static void LoadOutputPlugin(OutputPluginCallbacks *callbacks, char *plugin);
 
@@ -178,6 +181,7 @@ StartupDecodingContext(List *output_plugin_options,
 	ctx->reorder->begin = begin_cb_wrapper;
 	ctx->reorder->apply_change = change_cb_wrapper;
 	ctx->reorder->commit = commit_cb_wrapper;
+	ctx->reorder->message = message_cb_wrapper;
 
 	ctx->out = makeStringInfo();
 	ctx->prepare_write = prepare_write;
@@ -702,6 +706,40 @@ filter_by_origin_cb_wrapper(LogicalDecodingContext *ctx, RepOriginId origin_id)
 	return ret;
 }
 
+static void
+message_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
+				   XLogRecPtr message_lsn, bool transactional,
+				   const char *prefix, Size message_size, const char *message)
+{
+	LogicalDecodingContext *ctx = cache->private_data;
+	LogicalErrorCallbackState state;
+	ErrorContextCallback errcallback;
+
+	if (ctx->callbacks.message_cb == NULL)
+		return;
+
+	/* Push callback + info on the error context stack */
+	state.ctx = ctx;
+	state.callback_name = "message";
+	state.report_location = message_lsn;
+	errcallback.callback = output_plugin_error_callback;
+	errcallback.arg = (void *) &state;
+	errcallback.previous = error_context_stack;
+	error_context_stack = &errcallback;
+
+	/* set output state */
+	ctx->accept_writes = true;
+	ctx->write_xid = txn != NULL ? txn->xid : InvalidTransactionId;
+	ctx->write_location = message_lsn;
+
+	/* do the actual work: call callback */
+	ctx->callbacks.message_cb(ctx, txn, message_lsn, transactional, prefix,
+							  message_size, message);
+
+	/* Pop the error context stack */
+	error_context_stack = errcallback.previous;
+}
+
 /*
  * Set the required catalog xmin horizon for historic snapshots in the current
  * replication slot.
diff --git a/src/backend/replication/logical/logicalfuncs.c b/src/backend/replication/logical/logicalfuncs.c
index dd6cd62..69d2000 100644
--- a/src/backend/replication/logical/logicalfuncs.c
+++ b/src/backend/replication/logical/logicalfuncs.c
@@ -24,6 +24,8 @@
 #include "access/xlog_internal.h"
 #include "access/xlogutils.h"
 
+#include "access/xact.h"
+
 #include "catalog/pg_type.h"
 
 #include "nodes/makefuncs.h"
@@ -41,6 +43,7 @@
 #include "replication/decode.h"
 #include "replication/logical.h"
 #include "replication/logicalfuncs.h"
+#include "replication/message.h"
 
 #include "storage/fd.h"
 
@@ -380,3 +383,27 @@ pg_logical_slot_peek_binary_changes(PG_FUNCTION_ARGS)
 {
 	return pg_logical_slot_get_changes_guts(fcinfo, false, true);
 }
+
+
+/*
+ * SQL function for writing logical decding message into WAL.
+ */
+Datum
+pg_logical_emit_message_bytea(PG_FUNCTION_ARGS)
+{
+	bool		transactional = PG_GETARG_BOOL(0);
+	char	   *prefix = text_to_cstring(PG_GETARG_TEXT_PP(1));
+	bytea	   *data = PG_GETARG_BYTEA_PP(2);
+	XLogRecPtr	lsn;
+
+	lsn = LogLogicalMessage(prefix, VARDATA_ANY(data), VARSIZE_ANY_EXHDR(data),
+							transactional);
+	PG_RETURN_LSN(lsn);
+}
+
+Datum
+pg_logical_emit_message_text(PG_FUNCTION_ARGS)
+{
+	/* bytea and text are compatible */
+	return pg_logical_emit_message_bytea(fcinfo);
+}
diff --git a/src/backend/replication/logical/message.c b/src/backend/replication/logical/message.c
new file mode 100644
index 0000000..684f799
--- /dev/null
+++ b/src/backend/replication/logical/message.c
@@ -0,0 +1,87 @@
+/*-------------------------------------------------------------------------
+ *
+ * message.c
+ *	  Generic logical messages.
+ *
+ * Copyright (c) 2013-2016, PostgreSQL Global Development Group
+ *
+ * IDENTIFICATION
+ *	  src/backend/replication/logical/message.c
+ *
+ * NOTES
+ *
+ * Generic logical messages allow XLOG logging of arbitrary binary blobs that
+ * get passed to the logical decoding plugin. In normal XLOG processing they
+ * are same as NOOP.
+ *
+ * These messages can be either transactional or non-transactional.
+ * Transactional messages are part of current transaction and will be sent to
+ * decoding plugin using in a same way as DML operations.
+ * Non-transactional messages are sent to the plugin at the time when the
+ * logical decoding reads them from XLOG. This also means that transactional
+ * messages won't be delivered if the transaction was rolled back but the
+ * non-transactional one will be delivered always.
+ *
+ * Every message carries prefix to avoid conflicts between different decoding
+ * plugins. The plugin authors must take extra care to use unique prefix,
+ * good options seems to be for example to use the name of the extension.
+ *
+ * ---------------------------------------------------------------------------
+ */
+
+#include "postgres.h"
+
+#include "access/xact.h"
+
+#include "catalog/indexing.h"
+
+#include "nodes/execnodes.h"
+
+#include "replication/message.h"
+#include "replication/logical.h"
+
+#include "utils/memutils.h"
+
+/*
+ * Write logical decoding message into XLog.
+ */
+XLogRecPtr
+LogLogicalMessage(const char *prefix, const char *message, size_t size,
+				  bool transactional)
+{
+	xl_logical_message	xlrec;
+
+	/*
+	 * Force xid to be allocated if we're emitting a transactional message.
+	 */
+	if (transactional)
+	{
+		Assert(IsTransactionState());
+		GetCurrentTransactionId();
+	}
+
+	xlrec.transactional = transactional;
+	xlrec.prefix_size = strlen(prefix) + 1;
+	xlrec.message_size = size;
+
+	XLogBeginInsert();
+	XLogRegisterData((char *) &xlrec, SizeOfLogicalMessage);
+	XLogRegisterData((char *) prefix, xlrec.prefix_size);
+	XLogRegisterData((char *) message, size);
+
+	return XLogInsert(RM_LOGICALMSG_ID, XLOG_LOGICAL_MESSAGE);
+}
+
+/*
+ * Redo is basically just noop for logical decoding messages.
+ */
+void
+logicalmsg_redo(XLogReaderState *record)
+{
+	uint8		info = XLogRecGetInfo(record) & ~XLR_INFO_MASK;
+
+	if (info != XLOG_LOGICAL_MESSAGE)
+			elog(PANIC, "logicalmsg_redo: unknown op code %u", info);
+
+	/* This is only interesting for logical decoding, see decode.c. */
+}
diff --git a/src/backend/replication/logical/reorderbuffer.c b/src/backend/replication/logical/reorderbuffer.c
index 9d78c8c..52c6986 100644
--- a/src/backend/replication/logical/reorderbuffer.c
+++ b/src/backend/replication/logical/reorderbuffer.c
@@ -414,6 +414,14 @@ ReorderBufferReturnChange(ReorderBuffer *rb, ReorderBufferChange *change)
 				change->data.tp.oldtuple = NULL;
 			}
 			break;
+		case REORDER_BUFFER_CHANGE_MESSAGE:
+			if (change->data.msg.prefix != NULL)
+				pfree(change->data.msg.prefix);
+			change->data.msg.prefix = NULL;
+			if (change->data.msg.message != NULL)
+				pfree(change->data.msg.message);
+			change->data.msg.message = NULL;
+			break;
 		case REORDER_BUFFER_CHANGE_INTERNAL_SNAPSHOT:
 			if (change->data.snapshot)
 			{
@@ -627,6 +635,61 @@ ReorderBufferQueueChange(ReorderBuffer *rb, TransactionId xid, XLogRecPtr lsn,
 	ReorderBufferCheckSerializeTXN(rb, txn);
 }
 
+/*
+ * Queue message into a transaction so it can be processed upon commit.
+ */
+void
+ReorderBufferQueueMessage(ReorderBuffer *rb, TransactionId xid,
+						  Snapshot snapshot, XLogRecPtr lsn,
+						  bool transactional, const char *prefix,
+						  Size message_size, const char *message)
+{
+	if (transactional)
+	{
+		MemoryContext oldcontext;
+		ReorderBufferChange *change;
+
+		Assert(xid != InvalidTransactionId);
+
+		oldcontext = MemoryContextSwitchTo(rb->context);
+
+		change = ReorderBufferGetChange(rb);
+		change->action = REORDER_BUFFER_CHANGE_MESSAGE;
+		change->data.msg.prefix = pstrdup(prefix);
+		change->data.msg.message_size = message_size;
+		change->data.msg.message = palloc(message_size);
+		memcpy(change->data.msg.message, message, message_size);
+
+		ReorderBufferQueueChange(rb, xid, lsn, change);
+
+		MemoryContextSwitchTo(oldcontext);
+	}
+	else
+	{
+		ReorderBufferTXN   *txn = NULL;
+		volatile Snapshot	snapshot_now = snapshot;
+
+		if (xid != InvalidTransactionId)
+			txn = ReorderBufferTXNByXid(rb, xid, true, NULL, lsn, true);
+
+		/* setup snapshot to allow catalog access */
+		SetupHistoricSnapshot(snapshot_now, NULL);
+		PG_TRY();
+		{
+			rb->message(rb, txn, lsn, false, prefix, message_size, message);
+
+			TeardownHistoricSnapshot(false);
+		}
+		PG_CATCH();
+		{
+			TeardownHistoricSnapshot(true);
+			PG_RE_THROW();
+		}
+		PG_END_TRY();
+	}
+}
+
+
 static void
 AssertTXNLsnOrder(ReorderBuffer *rb)
 {
@@ -1493,6 +1556,13 @@ ReorderBufferCommit(ReorderBuffer *rb, TransactionId xid,
 					specinsert = change;
 					break;
 
+				case REORDER_BUFFER_CHANGE_MESSAGE:
+					rb->message(rb, txn, change->lsn, true,
+								change->data.msg.prefix,
+								change->data.msg.message_size,
+								change->data.msg.message);
+					break;
+
 				case REORDER_BUFFER_CHANGE_INTERNAL_SNAPSHOT:
 					/* get rid of the old */
 					TeardownHistoricSnapshot(false);
@@ -2159,6 +2229,33 @@ ReorderBufferSerializeChange(ReorderBuffer *rb, ReorderBufferTXN *txn,
 				}
 				break;
 			}
+		case REORDER_BUFFER_CHANGE_MESSAGE:
+			{
+				char	   *data;
+				Size		prefix_size = strlen(change->data.msg.prefix) + 1;
+
+				sz += prefix_size + change->data.msg.message_size +
+					sizeof(Size) + sizeof(Size);
+				ReorderBufferSerializeReserve(rb, sz);
+
+				data = ((char *) rb->outbuf) + sizeof(ReorderBufferDiskChange);
+
+				/* write the prefix including the size */
+				memcpy(data, &prefix_size, sizeof(Size));
+				data += sizeof(Size);
+				memcpy(data, change->data.msg.prefix,
+					   prefix_size);
+				data += prefix_size;
+
+				/* write the message including the size */
+				memcpy(data, &change->data.msg.message_size, sizeof(Size));
+				data += sizeof(Size);
+				memcpy(data, change->data.msg.message,
+					   change->data.msg.message_size);
+				data += change->data.msg.message_size;
+
+				break;
+			}
 		case REORDER_BUFFER_CHANGE_INTERNAL_SNAPSHOT:
 			{
 				Snapshot	snap;
@@ -2415,6 +2512,30 @@ ReorderBufferRestoreChange(ReorderBuffer *rb, ReorderBufferTXN *txn,
 			}
 
 			break;
+		case REORDER_BUFFER_CHANGE_MESSAGE:
+			{
+				Size		prefix_size;
+
+				/* read prefix */
+				memcpy(&prefix_size, data, sizeof(Size));
+				data += sizeof(Size);
+				change->data.msg.prefix = MemoryContextAlloc(rb->context,
+															 prefix_size);
+				memcpy(change->data.msg.prefix, data, prefix_size);
+				Assert(change->data.msg.prefix[prefix_size-1] == '\0');
+				data += prefix_size;
+
+				/* read the messsage */
+				memcpy(&change->data.msg.message_size, data, sizeof(Size));
+				data += sizeof(Size);
+				change->data.msg.message = MemoryContextAlloc(rb->context,
+												change->data.msg.message_size);
+				memcpy(change->data.msg.message, data,
+					   change->data.msg.message_size);
+				data += change->data.msg.message_size;
+
+				break;
+			}
 		case REORDER_BUFFER_CHANGE_INTERNAL_SNAPSHOT:
 			{
 				Snapshot	oldsnap;
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index 179b85a..b4dc617 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -605,6 +605,25 @@ SnapBuildExportSnapshot(SnapBuild *builder)
 }
 
 /*
+ * Ensure there is a snapshot and if not build one for current transaction.
+ */
+Snapshot
+SnapBuildGetOrBuildSnapshot(SnapBuild *builder, TransactionId xid)
+{
+	Assert(builder->state == SNAPBUILD_CONSISTENT);
+
+	/* only build a new snapshot if we don't have a prebuilt one */
+	if (builder->snapshot == NULL)
+	{
+		builder->snapshot = SnapBuildBuildSnapshot(builder, xid);
+		/* inrease refcount for the snapshot builder */
+		SnapBuildSnapIncRefcount(builder->snapshot);
+	}
+
+	return builder->snapshot;
+}
+
+/*
  * Reset a previously SnapBuildExportSnapshot()'ed snapshot if there is
  * any. Aborts the previously started transaction and resets the resource
  * owner back to its original value.
diff --git a/src/bin/pg_xlogdump/.gitignore b/src/bin/pg_xlogdump/.gitignore
index 33a1acf..c4783f1 100644
--- a/src/bin/pg_xlogdump/.gitignore
+++ b/src/bin/pg_xlogdump/.gitignore
@@ -1,23 +1,4 @@
 /pg_xlogdump
 # Source files copied from src/backend/access/rmgrdesc/
-/brindesc.c
-/clogdesc.c
-/committsdesc.c
-/dbasedesc.c
-/genericdesc.c
-/gindesc.c
-/gistdesc.c
-/hashdesc.c
-/heapdesc.c
-/mxactdesc.c
-/nbtdesc.c
-/relmapdesc.c
-/replorigindesc.c
-/seqdesc.c
-/smgrdesc.c
-/spgdesc.c
-/standbydesc.c
-/tblspcdesc.c
-/xactdesc.c
-/xlogdesc.c
+/*desc.c
 /xlogreader.c
diff --git a/src/bin/pg_xlogdump/rmgrdesc.c b/src/bin/pg_xlogdump/rmgrdesc.c
index cff7e59..017b9c5 100644
--- a/src/bin/pg_xlogdump/rmgrdesc.c
+++ b/src/bin/pg_xlogdump/rmgrdesc.c
@@ -26,6 +26,7 @@
 #include "commands/dbcommands_xlog.h"
 #include "commands/sequence.h"
 #include "commands/tablespace.h"
+#include "replication/message.h"
 #include "replication/origin.h"
 #include "rmgrdesc.h"
 #include "storage/standbydefs.h"
diff --git a/src/include/access/rmgrlist.h b/src/include/access/rmgrlist.h
index 3cfe6f7..a7a0ae2 100644
--- a/src/include/access/rmgrlist.h
+++ b/src/include/access/rmgrlist.h
@@ -46,3 +46,4 @@ PG_RMGR(RM_BRIN_ID, "BRIN", brin_redo, brin_desc, brin_identify, NULL, NULL)
 PG_RMGR(RM_COMMIT_TS_ID, "CommitTs", commit_ts_redo, commit_ts_desc, commit_ts_identify, NULL, NULL)
 PG_RMGR(RM_REPLORIGIN_ID, "ReplicationOrigin", replorigin_redo, replorigin_desc, replorigin_identify, NULL, NULL)
 PG_RMGR(RM_GENERIC_ID, "Generic", generic_redo, generic_desc, generic_identify, NULL, NULL)
+PG_RMGR(RM_LOGICALMSG_ID, "LogicalMessage", logicalmsg_redo, logicalmsg_desc, logicalmsg_identify, NULL, NULL)
diff --git a/src/include/catalog/pg_proc.h b/src/include/catalog/pg_proc.h
index c86b920..e5d20f0 100644
--- a/src/include/catalog/pg_proc.h
+++ b/src/include/catalog/pg_proc.h
@@ -5125,6 +5125,10 @@ DATA(insert OID = 3784 (  pg_logical_slot_peek_changes PGNSP PGUID 12 1000 1000
 DESCR("peek at changes from replication slot");
 DATA(insert OID = 3785 (  pg_logical_slot_peek_binary_changes PGNSP PGUID 12 1000 1000 25 0 f f f f f t v u 4 0 2249 "19 3220 23 1009" "{19,3220,23,1009,3220,28,17}" "{i,i,i,v,o,o,o}" "{slot_name,upto_lsn,upto_nchanges,options,location,xid,data}" _null_ _null_ pg_logical_slot_peek_binary_changes _null_ _null_ _null_ ));
 DESCR("peek at binary changes from replication slot");
+DATA(insert OID = 3577 (  pg_logical_emit_message PGNSP PGUID 12 1 0 0 0 f f f f t f v u 3 0 3220 "16 25 25" _null_ _null_ _null_ _null_ _null_ pg_logical_emit_message_text _null_ _null_ _null_ ));
+DESCR("emit a textual logical decoding message");
+DATA(insert OID = 3578 (  pg_logical_emit_message PGNSP PGUID 12 1 0 0 0 f f f f t f v u 3 0 3220 "16 25 17" _null_ _null_ _null_ _null_ _null_ pg_logical_emit_message_bytea _null_ _null_ _null_ ));
+DESCR("emit a binary logical decoding message");
 
 /* event triggers */
 DATA(insert OID = 3566 (  pg_event_trigger_dropped_objects		PGNSP PGUID 12 10 100 0 0 f f f f t t s s 0 0 2249 "" "{26,26,23,16,16,16,25,25,25,25,1009,1009}" "{o,o,o,o,o,o,o,o,o,o,o,o}" "{classid, objid, objsubid, original, normal, is_temporary, object_type, schema_name, object_name, object_identity, address_names, address_args}" _null_ _null_ pg_event_trigger_dropped_objects _null_ _null_ _null_ ));
diff --git a/src/include/replication/logicalfuncs.h b/src/include/replication/logicalfuncs.h
index c87a1df..5540414 100644
--- a/src/include/replication/logicalfuncs.h
+++ b/src/include/replication/logicalfuncs.h
@@ -21,4 +21,6 @@ extern Datum pg_logical_slot_get_binary_changes(PG_FUNCTION_ARGS);
 extern Datum pg_logical_slot_peek_changes(PG_FUNCTION_ARGS);
 extern Datum pg_logical_slot_peek_binary_changes(PG_FUNCTION_ARGS);
 
+extern Datum pg_logical_emit_message_bytea(PG_FUNCTION_ARGS);
+extern Datum pg_logical_emit_message_text(PG_FUNCTION_ARGS);
 #endif
diff --git a/src/include/replication/message.h b/src/include/replication/message.h
new file mode 100644
index 0000000..8b968d5
--- /dev/null
+++ b/src/include/replication/message.h
@@ -0,0 +1,41 @@
+/*-------------------------------------------------------------------------
+ * message.h
+ *	   Exports from replication/logical/message.c
+ *
+ * Copyright (c) 2013-2016, PostgreSQL Global Development Group
+ *
+ * src/include/replication/message.h
+ *-------------------------------------------------------------------------
+ */
+#ifndef PG_LOGICAL_MESSAGE_H
+#define PG_LOGICAL_MESSAGE_H
+
+#include "access/xlog.h"
+#include "access/xlogdefs.h"
+#include "access/xlogreader.h"
+
+/*
+ * Generic logical decoding message wal record.
+ */
+typedef struct xl_logical_message
+{
+	bool		transactional;					/* is message transactional? */
+	Size		prefix_size;					/* length of prefix */
+	Size		message_size;					/* size of the message */
+	char		message[FLEXIBLE_ARRAY_MEMBER];	/* message including the null
+												 * terminated prefix of length
+												 * prefix_size */
+} xl_logical_message;
+
+#define SizeOfLogicalMessage	(offsetof(xl_logical_message, message))
+
+extern XLogRecPtr LogLogicalMessage(const char *prefix, const char *message,
+									size_t size, bool transactional);
+
+/* RMGR API*/
+#define XLOG_LOGICAL_MESSAGE	0x00
+void		logicalmsg_redo(XLogReaderState *record);
+void		logicalmsg_desc(StringInfo buf, XLogReaderState *record);
+const char *logicalmsg_identify(uint8 info);
+
+#endif   /* PG_LOGICAL_MESSAGE_H */
diff --git a/src/include/replication/output_plugin.h b/src/include/replication/output_plugin.h
index 577b12e..3a2ca98 100644
--- a/src/include/replication/output_plugin.h
+++ b/src/include/replication/output_plugin.h
@@ -74,6 +74,18 @@ typedef void (*LogicalDecodeCommitCB) (
 												   XLogRecPtr commit_lsn);
 
 /*
+ * Called for the generic logical decoding messages.
+ */
+typedef void (*LogicalDecodeMessageCB) (
+											 struct LogicalDecodingContext *,
+											 ReorderBufferTXN *txn,
+											 XLogRecPtr message_lsn,
+											 bool transactional,
+											 const char *prefix,
+											 Size message_size,
+											 const char *message);
+
+/*
  * Filter changes by origin.
  */
 typedef bool (*LogicalDecodeFilterByOriginCB) (
@@ -96,6 +108,7 @@ typedef struct OutputPluginCallbacks
 	LogicalDecodeBeginCB begin_cb;
 	LogicalDecodeChangeCB change_cb;
 	LogicalDecodeCommitCB commit_cb;
+	LogicalDecodeMessageCB message_cb;
 	LogicalDecodeFilterByOriginCB filter_by_origin_cb;
 	LogicalDecodeShutdownCB shutdown_cb;
 } OutputPluginCallbacks;
diff --git a/src/include/replication/reorderbuffer.h b/src/include/replication/reorderbuffer.h
index b52d06a..4c54953 100644
--- a/src/include/replication/reorderbuffer.h
+++ b/src/include/replication/reorderbuffer.h
@@ -54,6 +54,7 @@ enum ReorderBufferChangeType
 	REORDER_BUFFER_CHANGE_INSERT,
 	REORDER_BUFFER_CHANGE_UPDATE,
 	REORDER_BUFFER_CHANGE_DELETE,
+	REORDER_BUFFER_CHANGE_MESSAGE,
 	REORDER_BUFFER_CHANGE_INTERNAL_SNAPSHOT,
 	REORDER_BUFFER_CHANGE_INTERNAL_COMMAND_ID,
 	REORDER_BUFFER_CHANGE_INTERNAL_TUPLECID,
@@ -98,6 +99,14 @@ typedef struct ReorderBufferChange
 			ReorderBufferTupleBuf *newtuple;
 		}			tp;
 
+		/* Message with arbitrary data. */
+		struct
+		{
+			char   *prefix;
+			Size	message_size;
+			char   *message;
+		} msg;
+
 		/* New snapshot, set when action == *_INTERNAL_SNAPSHOT */
 		Snapshot	snapshot;
 
@@ -274,6 +283,15 @@ typedef void (*ReorderBufferCommitCB) (
 												   ReorderBufferTXN *txn,
 												   XLogRecPtr commit_lsn);
 
+/* message callback signature */
+typedef void (*ReorderBufferMessageCB) (
+												   ReorderBuffer *rb,
+												   ReorderBufferTXN *txn,
+												   XLogRecPtr message_lsn,
+												   bool transactional,
+												   const char *prefix, Size sz,
+												   const char *message);
+
 struct ReorderBuffer
 {
 	/*
@@ -300,6 +318,7 @@ struct ReorderBuffer
 	ReorderBufferBeginCB begin;
 	ReorderBufferApplyChangeCB apply_change;
 	ReorderBufferCommitCB commit;
+	ReorderBufferMessageCB message;
 
 	/*
 	 * Pointer that will be passed untouched to the callbacks.
@@ -350,6 +369,9 @@ ReorderBufferChange *ReorderBufferGetChange(ReorderBuffer *);
 void		ReorderBufferReturnChange(ReorderBuffer *, ReorderBufferChange *);
 
 void		ReorderBufferQueueChange(ReorderBuffer *, TransactionId, XLogRecPtr lsn, ReorderBufferChange *);
+void		ReorderBufferQueueMessage(ReorderBuffer *, TransactionId, Snapshot snapshot, XLogRecPtr lsn,
+									  bool transactional, const char *prefix,
+									  Size message_size, const char *message);
 void ReorderBufferCommit(ReorderBuffer *, TransactionId,
 					XLogRecPtr commit_lsn, XLogRecPtr end_lsn,
 	  TimestampTz commit_time, RepOriginId origin_id, XLogRecPtr origin_lsn);
diff --git a/src/include/replication/snapbuild.h b/src/include/replication/snapbuild.h
index 75955af..c4127a1 100644
--- a/src/include/replication/snapbuild.h
+++ b/src/include/replication/snapbuild.h
@@ -63,6 +63,8 @@ extern const char *SnapBuildExportSnapshot(SnapBuild *snapstate);
 extern void SnapBuildClearExportedSnapshot(void);
 
 extern SnapBuildState SnapBuildCurrentState(SnapBuild *snapstate);
+extern Snapshot SnapBuildGetOrBuildSnapshot(SnapBuild *builder,
+											TransactionId xid);
 
 extern bool SnapBuildXactNeedsSkip(SnapBuild *snapstate, XLogRecPtr ptr);
 
-- 
1.9.1

diff --git a/contrib/test_decoding/expected/messages.out b/contrib/test_decoding/expected/messages.out
index 70130e9..a5b13c5 100644
--- a/contrib/test_decoding/expected/messages.out
+++ b/contrib/test_decoding/expected/messages.out
@@ -1,6 +1,5 @@
 -- predictability
 SET synchronous_commit = on;
-SET client_encoding = 'utf8';
 SELECT 'init' FROM pg_create_logical_replication_slot('regression_slot', 'test_decoding');
  ?column? 
 ----------
@@ -71,9 +70,32 @@ SELECT data FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'for
  message: transactional: 1 prefix: test, sz: 11 content:czechtastic
 (7 rows)
 
-SELECT 'init' FROM pg_drop_replication_slot('regression_slot');
+-- test db filtering
+CREATE DATABASE test_logical_messages;
+\set prevdb :DBNAME
+\c test_logical_messages
+SELECT 'otherdb1' FROM pg_logical_emit_message(false, 'test', 'otherdb1');
  ?column? 
 ----------
- init
+ otherdb1
+(1 row)
+
+SELECT 'otherdb2' FROM pg_logical_emit_message(true, 'test', 'otherdb2');
+ ?column? 
+----------
+ otherdb2
+(1 row)
+
+\c :prevdb
+SELECT data FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'force-binary', '0', 'skip-empty-xacts', '1');
+ data 
+------
+(0 rows)
+
+DROP DATABASE test_logical_messages;
+SELECT 'cleanup' FROM pg_drop_replication_slot('regression_slot');
+ ?column? 
+----------
+ cleanup
 (1 row)
 
diff --git a/contrib/test_decoding/expected/replorigin.out b/contrib/test_decoding/expected/replorigin.out
index c0f5125..8e8889d 100644
--- a/contrib/test_decoding/expected/replorigin.out
+++ b/contrib/test_decoding/expected/replorigin.out
@@ -59,6 +59,12 @@ SELECT pg_replication_origin_session_setup('test_decoding: regression_slot');
 -- ensure we prevent duplicate setup
 SELECT pg_replication_origin_session_setup('test_decoding: regression_slot');
 ERROR:  cannot setup replication origin when one is already setup
+SELECT 'this message will not be decoded' FROM pg_logical_emit_message(false, 'test', 'this message will not be decoded');
+             ?column?             
+----------------------------------
+ this message will not be decoded
+(1 row)
+
 BEGIN;
 -- setup transaction origin
 SELECT pg_replication_origin_xact_setup('0/aabbccdd', '2013-01-01 00:00');
diff --git a/contrib/test_decoding/sql/messages.sql b/contrib/test_decoding/sql/messages.sql
index 4aedb04..eba7d7a 100644
--- a/contrib/test_decoding/sql/messages.sql
+++ b/contrib/test_decoding/sql/messages.sql
@@ -1,6 +1,5 @@
 -- predictability
 SET synchronous_commit = on;
-SET client_encoding = 'utf8';
 
 SELECT 'init' FROM pg_create_logical_replication_slot('regression_slot', 'test_decoding');
 
@@ -22,4 +21,17 @@ SELECT 'ignorethis' FROM pg_logical_emit_message(true, 'test', 'czechtastic');
 
 SELECT data FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'force-binary', '0', 'skip-empty-xacts', '1');
 
-SELECT 'init' FROM pg_drop_replication_slot('regression_slot');
+-- test db filtering
+CREATE DATABASE test_logical_messages;
+\set prevdb :DBNAME
+\c test_logical_messages
+
+SELECT 'otherdb1' FROM pg_logical_emit_message(false, 'test', 'otherdb1');
+SELECT 'otherdb2' FROM pg_logical_emit_message(true, 'test', 'otherdb2');
+
+\c :prevdb
+SELECT data FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'force-binary', '0', 'skip-empty-xacts', '1');
+
+DROP DATABASE test_logical_messages;
+
+SELECT 'cleanup' FROM pg_drop_replication_slot('regression_slot');
diff --git a/contrib/test_decoding/sql/replorigin.sql b/contrib/test_decoding/sql/replorigin.sql
index e12404e..a33e460bb 100644
--- a/contrib/test_decoding/sql/replorigin.sql
+++ b/contrib/test_decoding/sql/replorigin.sql
@@ -31,6 +31,8 @@ SELECT pg_replication_origin_session_setup('test_decoding: regression_slot');
 -- ensure we prevent duplicate setup
 SELECT pg_replication_origin_session_setup('test_decoding: regression_slot');
 
+SELECT 'this message will not be decoded' FROM pg_logical_emit_message(false, 'test', 'this message will not be decoded');
+
 BEGIN;
 -- setup transaction origin
 SELECT pg_replication_origin_xact_setup('0/aabbccdd', '2013-01-01 00:00');
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index 3e80c4a..0cdb0b8 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -464,6 +464,15 @@ DecodeHeapOp(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
 	}
 }
 
+static inline bool
+FilterByOrigin(LogicalDecodingContext *ctx, RepOriginId origin_id)
+{
+	if (ctx->callbacks.filter_by_origin_cb == NULL)
+		return false;
+
+	return filter_by_origin_cb_wrapper(ctx, origin_id);
+}
+
 /*
  * Handle rmgr LOGICALMSG_ID records for DecodeRecordIntoReorderBuffer().
  */
@@ -474,6 +483,7 @@ DecodeLogicalMsgOp(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
 	XLogReaderState *r = buf->record;
 	TransactionId	xid = XLogRecGetXid(r);
 	uint8			info = XLogRecGetInfo(r) & ~XLR_INFO_MASK;
+	RepOriginId		origin_id = XLogRecGetOrigin(r);
 	Snapshot		snapshot;
 	xl_logical_message *message;
 
@@ -488,6 +498,10 @@ DecodeLogicalMsgOp(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
 
 	message = (xl_logical_message *) XLogRecGetData(r);
 
+	if (message->dbId != ctx->slot->data.database ||
+		FilterByOrigin(ctx, origin_id))
+		return;
+
 	if (message->transactional &&
 		!SnapBuildProcessChange(builder, xid, buf->origptr))
 		return;
@@ -504,15 +518,6 @@ DecodeLogicalMsgOp(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
 							  message->message + message->prefix_size);
 }
 
-static inline bool
-FilterByOrigin(LogicalDecodingContext *ctx, RepOriginId origin_id)
-{
-	if (ctx->callbacks.filter_by_origin_cb == NULL)
-		return false;
-
-	return filter_by_origin_cb_wrapper(ctx, origin_id);
-}
-
 /*
  * Consolidated commit record handling between the different form of commit
  * records.
diff --git a/src/backend/replication/logical/message.c b/src/backend/replication/logical/message.c
index 684f799..efcc25a 100644
--- a/src/backend/replication/logical/message.c
+++ b/src/backend/replication/logical/message.c
@@ -31,6 +31,8 @@
 
 #include "postgres.h"
 
+#include "miscadmin.h"
+
 #include "access/xact.h"
 
 #include "catalog/indexing.h"
@@ -60,6 +62,7 @@ LogLogicalMessage(const char *prefix, const char *message, size_t size,
 		GetCurrentTransactionId();
 	}
 
+	xlrec.dbId = MyDatabaseId;
 	xlrec.transactional = transactional;
 	xlrec.prefix_size = strlen(prefix) + 1;
 	xlrec.message_size = size;
@@ -69,6 +72,9 @@ LogLogicalMessage(const char *prefix, const char *message, size_t size,
 	XLogRegisterData((char *) prefix, xlrec.prefix_size);
 	XLogRegisterData((char *) message, size);
 
+	/* allow origin filtering */
+	XLogIncludeOrigin();
+
 	return XLogInsert(RM_LOGICALMSG_ID, XLOG_LOGICAL_MESSAGE);
 }
 
diff --git a/src/include/replication/message.h b/src/include/replication/message.h
index 8b968d5..c9fd477 100644
--- a/src/include/replication/message.h
+++ b/src/include/replication/message.h
@@ -19,6 +19,7 @@
  */
 typedef struct xl_logical_message
 {
+	Oid         dbId;							/* Oid of the database */
 	bool		transactional;					/* is message transactional? */
 	Size		prefix_size;					/* length of prefix */
 	Size		message_size;					/* size of the message */

diff --git a/contrib/test_decoding/expected/messages.out b/contrib/test_decoding/expected/messages.out
index 70130e9..c75d401 100644
--- a/contrib/test_decoding/expected/messages.out
+++ b/contrib/test_decoding/expected/messages.out
@@ -1,6 +1,5 @@
 -- predictability
 SET synchronous_commit = on;
-SET client_encoding = 'utf8';
 SELECT 'init' FROM pg_create_logical_replication_slot('regression_slot', 'test_decoding');
  ?column? 
 ----------
@@ -71,9 +70,30 @@ SELECT data FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'for
  message: transactional: 1 prefix: test, sz: 11 content:czechtastic
 (7 rows)
 
-SELECT 'init' FROM pg_drop_replication_slot('regression_slot');
+-- test db filtering
+\set prevdb :DBNAME
+\c template1
+SELECT 'otherdb1' FROM pg_logical_emit_message(false, 'test', 'otherdb1');
  ?column? 
 ----------
- init
+ otherdb1
+(1 row)
+
+SELECT 'otherdb2' FROM pg_logical_emit_message(true, 'test', 'otherdb2');
+ ?column? 
+----------
+ otherdb2
+(1 row)
+
+\c :prevdb
+SELECT data FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'force-binary', '0', 'skip-empty-xacts', '1');
+ data 
+------
+(0 rows)
+
+SELECT 'cleanup' FROM pg_drop_replication_slot('regression_slot');
+ ?column? 
+----------
+ cleanup
 (1 row)
 
diff --git a/contrib/test_decoding/expected/replorigin.out b/contrib/test_decoding/expected/replorigin.out
index c0f5125..8e8889d 100644
--- a/contrib/test_decoding/expected/replorigin.out
+++ b/contrib/test_decoding/expected/replorigin.out
@@ -59,6 +59,12 @@ SELECT pg_replication_origin_session_setup('test_decoding: regression_slot');
 -- ensure we prevent duplicate setup
 SELECT pg_replication_origin_session_setup('test_decoding: regression_slot');
 ERROR:  cannot setup replication origin when one is already setup
+SELECT 'this message will not be decoded' FROM pg_logical_emit_message(false, 'test', 'this message will not be decoded');
+             ?column?             
+----------------------------------
+ this message will not be decoded
+(1 row)
+
 BEGIN;
 -- setup transaction origin
 SELECT pg_replication_origin_xact_setup('0/aabbccdd', '2013-01-01 00:00');
diff --git a/contrib/test_decoding/sql/messages.sql b/contrib/test_decoding/sql/messages.sql
index 4aedb04..cf3f773 100644
--- a/contrib/test_decoding/sql/messages.sql
+++ b/contrib/test_decoding/sql/messages.sql
@@ -1,6 +1,5 @@
 -- predictability
 SET synchronous_commit = on;
-SET client_encoding = 'utf8';
 
 SELECT 'init' FROM pg_create_logical_replication_slot('regression_slot', 'test_decoding');
 
@@ -22,4 +21,14 @@ SELECT 'ignorethis' FROM pg_logical_emit_message(true, 'test', 'czechtastic');
 
 SELECT data FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'force-binary', '0', 'skip-empty-xacts', '1');
 
-SELECT 'init' FROM pg_drop_replication_slot('regression_slot');
+-- test db filtering
+\set prevdb :DBNAME
+\c template1
+
+SELECT 'otherdb1' FROM pg_logical_emit_message(false, 'test', 'otherdb1');
+SELECT 'otherdb2' FROM pg_logical_emit_message(true, 'test', 'otherdb2');
+
+\c :prevdb
+SELECT data FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'force-binary', '0', 'skip-empty-xacts', '1');
+
+SELECT 'cleanup' FROM pg_drop_replication_slot('regression_slot');
diff --git a/contrib/test_decoding/sql/replorigin.sql b/contrib/test_decoding/sql/replorigin.sql
index e12404e..a33e460bb 100644
--- a/contrib/test_decoding/sql/replorigin.sql
+++ b/contrib/test_decoding/sql/replorigin.sql
@@ -31,6 +31,8 @@ SELECT pg_replication_origin_session_setup('test_decoding: regression_slot');
 -- ensure we prevent duplicate setup
 SELECT pg_replication_origin_session_setup('test_decoding: regression_slot');
 
+SELECT 'this message will not be decoded' FROM pg_logical_emit_message(false, 'test', 'this message will not be decoded');
+
 BEGIN;
 -- setup transaction origin
 SELECT pg_replication_origin_xact_setup('0/aabbccdd', '2013-01-01 00:00');
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index 3e80c4a..0cdb0b8 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -464,6 +464,15 @@ DecodeHeapOp(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
 	}
 }
 
+static inline bool
+FilterByOrigin(LogicalDecodingContext *ctx, RepOriginId origin_id)
+{
+	if (ctx->callbacks.filter_by_origin_cb == NULL)
+		return false;
+
+	return filter_by_origin_cb_wrapper(ctx, origin_id);
+}
+
 /*
  * Handle rmgr LOGICALMSG_ID records for DecodeRecordIntoReorderBuffer().
  */
@@ -474,6 +483,7 @@ DecodeLogicalMsgOp(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
 	XLogReaderState *r = buf->record;
 	TransactionId	xid = XLogRecGetXid(r);
 	uint8			info = XLogRecGetInfo(r) & ~XLR_INFO_MASK;
+	RepOriginId		origin_id = XLogRecGetOrigin(r);
 	Snapshot		snapshot;
 	xl_logical_message *message;
 
@@ -488,6 +498,10 @@ DecodeLogicalMsgOp(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
 
 	message = (xl_logical_message *) XLogRecGetData(r);
 
+	if (message->dbId != ctx->slot->data.database ||
+		FilterByOrigin(ctx, origin_id))
+		return;
+
 	if (message->transactional &&
 		!SnapBuildProcessChange(builder, xid, buf->origptr))
 		return;
@@ -504,15 +518,6 @@ DecodeLogicalMsgOp(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
 							  message->message + message->prefix_size);
 }
 
-static inline bool
-FilterByOrigin(LogicalDecodingContext *ctx, RepOriginId origin_id)
-{
-	if (ctx->callbacks.filter_by_origin_cb == NULL)
-		return false;
-
-	return filter_by_origin_cb_wrapper(ctx, origin_id);
-}
-
 /*
  * Consolidated commit record handling between the different form of commit
  * records.
diff --git a/src/backend/replication/logical/message.c b/src/backend/replication/logical/message.c
index 684f799..efcc25a 100644
--- a/src/backend/replication/logical/message.c
+++ b/src/backend/replication/logical/message.c
@@ -31,6 +31,8 @@
 
 #include "postgres.h"
 
+#include "miscadmin.h"
+
 #include "access/xact.h"
 
 #include "catalog/indexing.h"
@@ -60,6 +62,7 @@ LogLogicalMessage(const char *prefix, const char *message, size_t size,
 		GetCurrentTransactionId();
 	}
 
+	xlrec.dbId = MyDatabaseId;
 	xlrec.transactional = transactional;
 	xlrec.prefix_size = strlen(prefix) + 1;
 	xlrec.message_size = size;
@@ -69,6 +72,9 @@ LogLogicalMessage(const char *prefix, const char *message, size_t size,
 	XLogRegisterData((char *) prefix, xlrec.prefix_size);
 	XLogRegisterData((char *) message, size);
 
+	/* allow origin filtering */
+	XLogIncludeOrigin();
+
 	return XLogInsert(RM_LOGICALMSG_ID, XLOG_LOGICAL_MESSAGE);
 }
 
diff --git a/src/include/replication/message.h b/src/include/replication/message.h
index 8b968d5..c9fd477 100644
--- a/src/include/replication/message.h
+++ b/src/include/replication/message.h
@@ -19,6 +19,7 @@
  */
 typedef struct xl_logical_message
 {
+	Oid         dbId;							/* Oid of the database */
 	bool		transactional;					/* is message transactional? */
 	Size		prefix_size;					/* length of prefix */
 	Size		message_size;					/* size of the message */