Override compile time log levels of specific messages/modules

diff --git a/GNUmakefile.in b/GNUmakefile.in
index 15fba9f..1a5dbfc 100644
--- a/GNUmakefile.in
+++ b/GNUmakefile.in
@@ -50,6 +50,8 @@ clean:
 	rm -rf tmp_install/
 # Garbage from autoconf:
 	@rm -rf autom4te.cache/
+# Remove MSGIDS file too
+	rm -f MSGIDS
 
 # Important: distclean `src' last, otherwise Makefile.global
 # will be gone too soon.
@@ -62,6 +64,7 @@ distclean maintainer-clean:
 # Garbage from autoconf:
 	@rm -rf autom4te.cache/
 	rm -f config.cache config.log config.status GNUmakefile
+	rm -f MSGIDS MSGMODULES
 
 check check-tests installcheck installcheck-parallel installcheck-tests:
 	$(MAKE) -C src/test/regress $@
diff --git a/config/create_msgids.sh b/config/create_msgids.sh
new file mode 100755
index 0000000..eb3391b
--- /dev/null
+++ b/config/create_msgids.sh
@@ -0,0 +1,55 @@
+#/usr/bin/env sh
+
+#
+# Run this script when configuring with --enable-genmsgids
+#
+# Recurse through all subdiectories, collecting information about all subdirs
+# which has a Makefile/GNUmakefile with "subdir = <subdir_name>" entry and
+# assign a module_id for all such subdirs. The Makefile.global then looks up
+# this catalog and uses the module_id configured.
+#
+# The script assumes that every subdir's Makefile has a specific pattern of
+# "^subdir = .*", which is thankfully true for subdirs that we care for
+#
+# We could be a lot smarter than what we are doing, especially avoiding
+# module_id assignment for subdirs which do not directly compile any files with
+# elog() messages.
+#
+MSG_MODULE=0
+handle_dir()
+{
+	MSG_MODULE=`expr $2 + 1`
+	for subdir in `ls $1`; do
+		if [ -d $1/$subdir ]; then
+			makefile1=$1/$subdir/Makefile
+			makefile2=$1/$subdir/GNUmakefile
+			if [ -f $makefile1 ]; then
+				cat $makefile1 | grep -E "^subdir = " > /dev/null
+				if [ $? -ne 0 ]; then
+					if [ -f $makefile2 ]; then
+						cat $makefile2 | grep -E "^subdir = " > /dev/null
+						if [ $? -eq 0 ]; then
+							makefile=$makefile2
+						else
+							continue
+						fi
+					else
+						continue
+					fi
+				else
+					makefile=$makefile1
+				fi
+			else
+				continue
+			fi
+			cat $makefile | grep -E "^subdir = " > /dev/null
+			if [ $? -eq 0 ]; then
+				moduledir=`cat $makefile | grep -E '^subdir = '`
+				echo $moduledir:${MSG_MODULE}
+			fi
+			handle_dir "$1/$subdir" $MSG_MODULE
+		fi
+	done
+}
+
+handle_dir "." $MSG_MODULE
diff --git a/configure b/configure
index 45c8eef..f5c2562 100755
--- a/configure
+++ b/configure
@@ -719,6 +719,7 @@ with_tcl
 enable_thread_safety
 INCLUDES
 autodepend
+genmsgids
 TAS
 GCC
 CPP
@@ -818,6 +819,7 @@ with_wal_blocksize
 with_wal_segsize
 with_CC
 enable_depend
+enable_genmsgids
 enable_cassert
 enable_thread_safety
 with_tcl
@@ -5234,6 +5236,35 @@ else
 
 fi
 
+#
+# Automatic msgids generation
+#
+
+
+# Check whether --enable-genmsgids was given.
+if test "${enable_genmsgids+set}" = set; then :
+  enableval=$enable_genmsgids;
+  case $enableval in
+    yes)
+
+$as_echo "#define USE_MODULE_MSGIDS 1" >>confdefs.h
+     
+      genmsgids=yes
+	  $srcdir/config/create_msgids.sh > MSGMODULES 2>&1
+
+      ;;
+    no)
+      :
+      ;;
+    *)
+      as_fn_error $? "no argument expected for --enable-genmsgids option" "$LINENO" 5
+      ;;
+  esac
+
+else
+  enable_genmsgids=no
+
+fi
 
 
 
diff --git a/configure.in b/configure.in
index c878b4e..f06bef9 100644
--- a/configure.in
+++ b/configure.in
@@ -555,7 +555,6 @@ PGAC_ARG_BOOL(enable, depend, no, [turn on automatic dependency tracking],
               [autodepend=yes])
 AC_SUBST(autodepend)
 
-
 #
 # Enable assert checks
 #
@@ -565,6 +564,14 @@ PGAC_ARG_BOOL(enable, cassert, no, [enable assertion checks (for debugging)],
 
 
 #
+# Enable module msgids
+#
+PGAC_ARG_BOOL(enable, genmsgids, no, [enable module msgids (for debugging)],
+              [AC_DEFINE([USE_MODULE_MSGIDS], 1,
+                         [Define to 1 to build with module msgids.  (--enable-genmsgids)])])
+AC_SUBST(genmsgids)
+
+#
 # Include directories
 #
 ac_save_IFS=$IFS
diff --git a/src/Makefile.global.in b/src/Makefile.global.in
index c211a2d..660431b 100644
--- a/src/Makefile.global.in
+++ b/src/Makefile.global.in
@@ -756,7 +756,6 @@ recurse = $(foreach target,$(if $1,$1,$(standard_targets)),$(foreach subdir,$(if
 # $3: target to run in subdir (defaults to current element of $1)
 recurse_always = $(foreach target,$(if $1,$1,$(standard_always_targets)),$(foreach subdir,$(if $2,$2,$(ALWAYS_SUBDIRS)),$(eval $(call _create_recursive_target,$(target),$(subdir),$(if $3,$3,$(target))))))
 
-
 ##########################################################################
 #
 # Automatic dependency generation
@@ -873,3 +872,41 @@ coverage-clean:
 	rm -f `find . -name '*.gcda' -print`
 
 endif # enable_coverage
+
+genmsgids = @genmsgids@
+
+ifeq ($(genmsgids), yes)
+PREPROCESS.c = $(CC) $(CFLAGS) $(CPPFLAGS) -E -P
+
+PGXL_MSG_FILEID := 1
+PGXL_MSG_MODULE := $(shell cat $(top_builddir)/MSGMODULES | grep -E "^subdir = $(subdir):" | cut -d ':' -f 2)
+
+ifeq ($(PGXL_MSG_MODULE)no, no)
+PGXL_MSG_MODULE := 255
+endif
+
+ifeq ($(autodepend), yes)
+ifeq ($(GCC), yes)
+
+# GCC allows us to create object and dependency file in one invocation.
+%.o : %.c
+	@if test ! -d $(DEPDIR); then mkdir -p $(DEPDIR); fi
+	$(PREPROCESS.c) -DPGXL_MSG_MODULE=$(PGXL_MSG_MODULE) -DPGXL_MSG_FILEID=$(PGXL_MSG_FILEID)  -o $@.E $< -MMD -MP -MF $(DEPDIR)/$(*F).Po
+	-cat $@.E | grep -E "do .*errstart|do .*elog_start" >> $(top_srcdir)/MSGIDS
+	-rm -f $@.E
+	$(COMPILE.c) -DPGXL_MSG_MODULE=$(PGXL_MSG_MODULE) -DPGXL_MSG_FILEID=$(PGXL_MSG_FILEID) -o $@ $< -MMD -MP -MF $(DEPDIR)/$(*F).Po
+	$(eval PGXL_MSG_FILEID := $(shell expr $(PGXL_MSG_FILEID) + 1))
+endif # GCC
+else
+ifeq ($(GCC), yes)
+%.o : %.c
+	$(PREPROCESS.c) -DPGXL_MSG_MODULE=$(PGXL_MSG_MODULE) -DPGXL_MSG_FILEID=$(PGXL_MSG_FILEID)  -o $@.E $<
+	-cat $@.E | grep -E "do .*errstart|do .*elog_start" >> $(top_srcdir)/MSGIDS
+	-rm -f $@.E
+	$(COMPILE.c) -DPGXL_MSG_MODULE=$(PGXL_MSG_MODULE) -DPGXL_MSG_FILEID=$(PGXL_MSG_FILEID) -o $@ $<
+	$(eval PGXL_MSG_FILEID := $(shell expr $(PGXL_MSG_FILEID) + 1))
+endif # GCC
+
+endif # autodepend
+
+endif # enable_genmsgids
diff --git a/src/backend/storage/ipc/ipci.c b/src/backend/storage/ipc/ipci.c
index c04b17f..2b7459c 100644
--- a/src/backend/storage/ipc/ipci.c
+++ b/src/backend/storage/ipc/ipci.c
@@ -145,6 +145,10 @@ CreateSharedMemoryAndSemaphores(bool makePrivate, int port)
 		size = add_size(size, ShmemBackendArraySize());
 #endif
 
+#ifdef USE_MODULE_MSGIDS
+		size = add_size(size, MsgModuleShmemSize());
+#endif
+
 		/* freeze the addin request size and include it */
 		addin_request_allowed = false;
 		size = add_size(size, total_addin_request);
@@ -263,6 +267,10 @@ CreateSharedMemoryAndSemaphores(bool makePrivate, int port)
 		ShmemBackendArrayAllocation();
 #endif
 
+#ifdef USE_MODULE_MSGIDS
+	MsgModuleShmemInit();
+#endif
+
 	/* Initialize dynamic shared memory facilities. */
 	if (!IsUnderPostmaster)
 		dsm_postmaster_startup(shim);
diff --git a/src/backend/tcop/postgres.c b/src/backend/tcop/postgres.c
index b185c1b..3b9b055 100644
--- a/src/backend/tcop/postgres.c
+++ b/src/backend/tcop/postgres.c
@@ -3804,6 +3804,10 @@ PostgresMain(int argc, char *argv[],
 	if (!IsUnderPostmaster)
 		PgStartTime = GetCurrentTimestamp();
 
+#ifdef USE_MODULE_MSGIDS
+	AtProcStart_MsgModule();
+#endif
+
 	/*
 	 * POSTGRES main processing loop begins here
 	 *
diff --git a/src/backend/utils/error/elog.c b/src/backend/utils/error/elog.c
index 78d441d..84ffabf 100644
--- a/src/backend/utils/error/elog.c
+++ b/src/backend/utils/error/elog.c
@@ -73,7 +73,9 @@
 #include "postmaster/syslogger.h"
 #include "storage/ipc.h"
 #include "storage/proc.h"
+#include "storage/procarray.h"
 #include "tcop/tcopprot.h"
+#include "utils/builtins.h"
 #include "utils/guc.h"
 #include "utils/memutils.h"
 #include "utils/ps_status.h"
@@ -84,6 +86,10 @@
 
 static const char *err_gettext(const char *str) pg_attribute_format_arg(1);
 static void set_errdata_field(MemoryContextData *cxt, char **ptr, const char *str);
+#ifdef USE_MODULE_MSGIDS
+static void AtProcExit_MsgModule(int code, Datum arg);
+static bool pg_msgmodule_enable_disable(int32 pid, bool enable);
+#endif
 
 /* Global variables */
 ErrorContextCallback *error_context_stack = NULL;
@@ -178,12 +184,41 @@ static const char *useful_strerror(int errnum);
 static const char *get_errno_symbol(int errnum);
 static const char *error_severity(int elevel);
 static void append_with_tabs(StringInfo buf, const char *str);
-static bool is_log_level_output(int elevel, int log_min_level);
+static bool is_log_level_output(int elevel,
+#ifdef USE_MODULE_MSGIDS
+		int moduleid,
+		int fileid,
+		int msgid,
+#endif
+		int log_min_level);
 static void write_pipe_chunks(char *data, int len, int dest);
 static void write_csvlog(ErrorData *edata);
 static void setup_formatted_log_time(void);
 static void setup_formatted_start_time(void);
 
+#ifdef USE_MODULE_MSGIDS
+typedef struct MsgModuleCtlStruct
+{
+	bool	mm_enabled;
+	bool	mm_persistent;
+	char	mm_flags[FLEXIBLE_ARRAY_MEMBER];
+} MsgModuleCtlStruct;
+
+#define StartOfBackendFlags 	\
+	( \
+	  PGXL_MSG_MAX_MODULES * \
+	  PGXL_MSG_MAX_FILEIDS_PER_MODULE * \
+	  PGXL_MSG_MAX_MSGIDS_PER_FILE \
+	)
+
+#define SizeOfMsgModuleCtlStruct	\
+	( \
+	  offsetof(MsgModuleCtlStruct, mm_flags) + \
+	  StartOfBackendFlags + \
+	  MaxBackends \
+	)
+static MsgModuleCtlStruct *MsgModuleCtl;
+#endif
 
 /*
  * in_error_recursion_trouble --- are we at risk of infinite error recursion?
@@ -231,6 +266,9 @@ err_gettext(const char *str)
  */
 bool
 errstart(int elevel, const char *filename, int lineno,
+#ifdef USE_MODULE_MSGIDS
+		int moduleid, int fileid, int msgid,
+#endif
 		 const char *funcname, const char *domain)
 {
 	ErrorData  *edata;
@@ -290,7 +328,13 @@ errstart(int elevel, const char *filename, int lineno,
 	 */
 
 	/* Determine whether message is enabled for server log output */
-	output_to_server = is_log_level_output(elevel, log_min_messages);
+	output_to_server = is_log_level_output(elevel,
+#ifdef USE_MODULE_MSGIDS
+			moduleid,
+			fileid,
+			msgid,
+#endif
+			log_min_messages);
 
 	/* Determine whether message is enabled for client output */
 	if (whereToSendOutput == DestRemote && elevel != LOG_SERVER_ONLY)
@@ -1295,7 +1339,11 @@ getinternalerrposition(void)
  * evaluating the format arguments if we do that.)
  */
 void
-elog_start(const char *filename, int lineno, const char *funcname)
+elog_start(const char *filename, int lineno,
+#ifdef USE_MODULE_MSGIDS
+		int moduleid, int fileid, int msgid,
+#endif
+		const char *funcname)
 {
 	ErrorData  *edata;
 
@@ -1334,6 +1382,11 @@ elog_start(const char *filename, int lineno, const char *funcname)
 	edata->filename = filename;
 	edata->lineno = lineno;
 	edata->funcname = funcname;
+#ifdef USE_MODULE_MSGIDS
+	edata->moduleid = moduleid;
+	edata->fileid = fileid;
+	edata->msgid = msgid;
+#endif
 	/* errno is saved now so that error parameter eval can't change it */
 	edata->saved_errno = errno;
 
@@ -1357,7 +1410,12 @@ elog_finish(int elevel, const char *fmt,...)
 	 */
 	errordata_stack_depth--;
 	errno = edata->saved_errno;
-	if (!errstart(elevel, edata->filename, edata->lineno, edata->funcname, NULL))
+	if (!errstart(elevel, edata->filename, edata->lineno,
+#ifdef USE_MODULE_MSGIDS
+				edata->moduleid,
+				edata->fileid, edata->msgid,
+#endif
+				edata->funcname, NULL))
 		return;					/* nothing to do */
 
 	/*
@@ -1612,6 +1670,10 @@ ThrowErrorData(ErrorData *edata)
 	MemoryContext oldcontext;
 
 	if (!errstart(edata->elevel, edata->filename, edata->lineno,
+#ifdef USE_MODULE_MSGIDS
+				edata->moduleid,
+				edata->fileid, edata->msgid,
+#endif
 				  edata->funcname, NULL))
 		return;
 
@@ -1745,7 +1807,12 @@ pg_re_throw(void)
 		 */
 		if (IsPostmasterEnvironment)
 			edata->output_to_server = is_log_level_output(FATAL,
-														  log_min_messages);
+#ifdef USE_MODULE_MSGIDS
+					0,
+					0,
+					0,
+#endif
+					log_min_messages);
 		else
 			edata->output_to_server = (FATAL >= log_min_messages);
 		if (whereToSendOutput == DestRemote)
@@ -2781,7 +2848,13 @@ write_csvlog(ErrorData *edata)
 	appendStringInfoChar(&buf, ',');
 
 	/* user query --- only reported if not disabled by the caller */
-	if (is_log_level_output(edata->elevel, log_min_error_statement) &&
+	if (is_log_level_output(edata->elevel,
+#ifdef USE_MODULE_MSGIDS
+				edata->moduleid,
+				edata->fileid,
+				edata->msgid,
+#endif
+				log_min_error_statement) &&
 		debug_query_string != NULL &&
 		!edata->hide_stmt)
 		print_stmt = true;
@@ -2939,7 +3012,13 @@ send_message_to_server_log(ErrorData *edata)
 	/*
 	 * If the user wants the query that generated this error logged, do it.
 	 */
-	if (is_log_level_output(edata->elevel, log_min_error_statement) &&
+	if (is_log_level_output(edata->elevel,
+#ifdef USE_MODULE_MSGIDS
+				edata->moduleid,
+				edata->fileid,
+				edata->msgid,
+#endif
+				log_min_error_statement) &&
 		debug_query_string != NULL &&
 		!edata->hide_stmt)
 	{
@@ -3687,6 +3766,70 @@ write_stderr(const char *fmt,...)
 	va_end(ap);
 }
 
+#ifdef USE_MODULE_MSGIDS
+static int
+get_overridden_log_level(int moduleid, int fileid, int msgid, int origlevel)
+{
+	uint32 position;
+	int value, relative, change, elevel;
+
+	/*
+	 * The shared memory may not set during init processing or in a stand alone
+	 * backend.
+	 */
+	if (!IsPostmasterEnvironment || IsInitProcessingMode())
+		return origlevel;
+
+	if (!MsgModuleCtl->mm_enabled)
+		return origlevel;
+
+	/*
+	 * Reject invalid bounds
+	 */
+	if ((moduleid <= 0 || moduleid >= PGXL_MSG_MAX_MODULES) ||
+		(fileid <= 0 || fileid >= PGXL_MSG_MAX_FILEIDS_PER_MODULE) ||
+		(msgid <= 0 || msgid >= PGXL_MSG_MAX_MSGIDS_PER_FILE))
+		return origlevel;
+
+	if (origlevel < DEBUG5 || origlevel >= LOG)
+		return origlevel;
+
+	if (!(MsgModuleCtl->mm_flags[StartOfBackendFlags + MyBackendId]))
+		return origlevel;
+
+	elevel = origlevel;
+
+	/*
+	 * Get the overridden log level and return it back
+	 */
+	position = (moduleid - 1) * PGXL_MSG_MAX_FILEIDS_PER_MODULE *
+			PGXL_MSG_MAX_MSGIDS_PER_FILE +
+			(fileid - 1) * PGXL_MSG_MAX_MSGIDS_PER_FILE +
+			(msgid - 1);
+	
+	/* Read once */
+	value = MsgModuleCtl->mm_flags[position];
+
+	relative = value & 0x80;
+	change = value & 0x7f;
+
+	if (value)
+	{
+		if (relative)
+		{
+			elevel = elevel + change;
+			if (elevel < DEBUG5)
+				elevel = DEBUG5;
+			else if (elevel >= LOG)
+				elevel = LOG;
+		}
+		else
+			elevel = change;
+		return elevel;
+	}
+	return origlevel;
+}
+#endif
 
 /*
  * is_log_level_output -- is elevel logically >= log_min_level?
@@ -3697,9 +3840,34 @@ write_stderr(const char *fmt,...)
  * test is correct for testing whether the message should go to the client.
  */
 static bool
-is_log_level_output(int elevel, int log_min_level)
+is_log_level_output(int elevel,
+#ifdef USE_MODULE_MSGIDS
+		int moduleid,
+		int fileid,
+		int msgid,
+#endif
+		int log_min_level)
 {
-	if (elevel == LOG || elevel == LOG_SERVER_ONLY)
+#ifdef USE_MODULE_MSGIDS
+	/* 
+	 * Check if the message's compile time value has been changed during the
+	 * run time.
+	 *
+	 * Currently, we only support increasing the log level of messages and that
+	 * too only for deciding whether the message should go to the server log or
+	 * not. A message which would otherwise not qualify to go to the server
+	 * log, thus can be forced to be logged. 
+	 *
+	 * In future, we may also want to go otherway round i.e. supressing a log
+	 * message or also change severity of log messages. The latter may
+	 * especially be useful to turn some specific ERROR messages into FATAL or
+	 * PANIC to be able to get a core dump for analysis.
+	 */
+	elevel = get_overridden_log_level(moduleid, fileid, msgid,
+			elevel);
+#endif
+
+	if (elevel == LOG || elevel == COMMERROR)
 	{
 		if (log_min_level == LOG || log_min_level <= ERROR)
 			return true;
@@ -3741,3 +3909,362 @@ trace_recovery(int trace_level)
 
 	return trace_level;
 }
+
+#ifdef USE_MODULE_MSGIDS
+Size
+MsgModuleShmemSize(void)
+{
+	/*
+	 * One byte per message to store overridden log level.
+	 * !!TODO We don't really need a byte and a few bits would be enough. So
+	 * look for improving this/
+	 *
+	 * What we have done is a very simplisitic representation of msg-ids. The
+	 * overall memory requirement of this representation is too large as
+	 * compared to the actual number of msgs. For example, both
+	 * PGXL_MSG_MAX_MSGIDS_PER_FILE and PGXL_MSG_MAX_FILEIDS_PER_MODULE are set
+	 * to the largest value that any one module uses, but the actual values are
+	 * much smaller
+	 *
+	 * Also have a separate area for MaxBackends so that caller can selectively
+	 * change logging for individual backends. Note that we don't support
+	 * having different logging levels for different backends. So either a
+	 * backend honours the module/file/msg level overrides or it does not.
+	 */
+	return SizeOfMsgModuleCtlStruct;
+}
+
+void
+MsgModuleShmemInit(void)
+{
+	bool found;
+
+	MsgModuleCtl = ShmemInitStruct("Message Module Struct",
+								   SizeOfMsgModuleCtlStruct,
+								   &found);
+}
+
+void
+AtProcStart_MsgModule(void)
+{
+	if (MsgModuleCtl->mm_persistent)
+		MsgModuleCtl->mm_flags[StartOfBackendFlags + MyBackendId] = true;
+	else
+		MsgModuleCtl->mm_flags[StartOfBackendFlags + MyBackendId] = false;
+	before_shmem_exit(AtProcExit_MsgModule, 0);
+}
+
+static bool
+pg_msgmodule_internal(int32 moduleid, int32 fileid, int32 msgid, char value)
+{
+	uint32 start_position;
+	uint32 len;
+
+	if (!superuser())
+		ereport(ERROR,
+				(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
+			 (errmsg("must be superuser to change elog message level"))));
+
+
+	if (moduleid <= 0 || moduleid >= PGXL_MSG_MAX_MODULES)
+		ereport(ERROR, (errmsg_internal("Invalid module id %d, allowed values 1-%d",
+						moduleid, PGXL_MSG_MAX_MODULES)));
+
+	if (fileid == -1)
+	{
+		/*
+		 * All messages in the given module to be overridden with the given
+		 * level
+		 */
+		len = PGXL_MSG_MAX_FILEIDS_PER_MODULE * PGXL_MSG_MAX_MSGIDS_PER_FILE;
+		start_position = (moduleid - 1) * len;
+		memset(MsgModuleCtl->mm_flags + start_position, value, len);
+		goto success;
+	}
+	else
+	{
+		if (fileid <= 0 || fileid >= PGXL_MSG_MAX_FILEIDS_PER_MODULE)
+			ereport(ERROR, (errmsg_internal("Invalid file id %d, allowed values 1-%d",
+							fileid, PGXL_MSG_MAX_FILEIDS_PER_MODULE)));
+		
+		/*
+		 * All messages in the given <module, file> to be overridden with the
+		 * given level
+		 */
+		if (msgid == -1)
+		{
+			len = PGXL_MSG_MAX_MSGIDS_PER_FILE;
+			start_position = ((moduleid - 1) * PGXL_MSG_MAX_FILEIDS_PER_MODULE * PGXL_MSG_MAX_MSGIDS_PER_FILE) +
+						(fileid - 1) * PGXL_MSG_MAX_MSGIDS_PER_FILE;
+			memset(MsgModuleCtl->mm_flags + start_position, value, len);
+			goto success;
+		}
+
+		if (msgid <= 0 || msgid >= PGXL_MSG_MAX_MSGIDS_PER_FILE)
+			ereport(ERROR, (errmsg_internal("Invalid msg id %d, allowed values 1-%d",
+							fileid, PGXL_MSG_MAX_MSGIDS_PER_FILE)));
+
+		/*
+		 * Deal with a specific <module, file, msg>
+		 */
+		len = sizeof (char);
+		start_position = ((moduleid - 1) * PGXL_MSG_MAX_FILEIDS_PER_MODULE * PGXL_MSG_MAX_MSGIDS_PER_FILE) +
+			((fileid - 1) * PGXL_MSG_MAX_MSGIDS_PER_FILE) +
+			(msgid - 1);
+		memset(MsgModuleCtl->mm_flags + start_position, value, len);
+		goto success;
+	}
+
+success:
+	return true;
+}
+
+Datum
+pg_msgmodule_set(PG_FUNCTION_ARGS)
+{
+	int32 moduleid = PG_GETARG_INT32(0);
+	int32 fileid = PG_GETARG_INT32(1);
+	int32 msgid = PG_GETARG_INT32(2);
+	const char *levelstr = PG_GETARG_CSTRING(3);
+	int32 level;
+
+	if (!superuser())
+		ereport(ERROR,
+				(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
+			 (errmsg("must be superuser to change elog message level"))));
+
+	/*
+	 * The only accepted values for the log levels are - LOG, DEBUG[1-5] and
+	 * DEFAULT
+	 */
+	if (strcasecmp(levelstr, "LOG") == 0)
+		level = LOG;
+	else if (strcasecmp(levelstr, "DEFAULT") == 0)
+		level = 0;
+	else if (strcasecmp(levelstr, "DEBUG1") == 0)
+		level = DEBUG1;
+	else if (strcasecmp(levelstr, "DEBUG2") == 0)
+		level = DEBUG2;
+	else if (strcasecmp(levelstr, "DEBUG3") == 0)
+		level = DEBUG3;
+	else if (strcasecmp(levelstr, "DEBUG4") == 0)
+		level = DEBUG4;
+	else if (strcasecmp(levelstr, "DEBUG5") == 0)
+		level = DEBUG5;
+	else
+		ereport(ERROR,
+				(errcode(ERRCODE_INTERNAL_ERROR),
+				 (errmsg("Invalid value \"%s\" for log level", levelstr))));
+
+	PG_RETURN_BOOL(pg_msgmodule_internal(moduleid, fileid, msgid, level));
+}
+
+Datum
+pg_msgmodule_change(PG_FUNCTION_ARGS)
+{
+	int32 moduleid = PG_GETARG_INT32(0);
+	int32 fileid = PG_GETARG_INT32(1);
+	int32 msgid = PG_GETARG_INT32(2);
+	int32 change = PG_GETARG_INT32(3);
+	int level;
+
+	if (!superuser())
+		ereport(ERROR,
+				(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
+			 (errmsg("must be superuser to change elog message level"))));
+	
+	if ((change < (DEBUG5 - LOG)) || (change > (LOG - DEBUG5)))
+		ereport(ERROR,
+				(errcode(ERRCODE_INTERNAL_ERROR),
+			 (errmsg("accepted values are between %d and +%d", DEBUG5 - LOG, LOG -
+					 DEBUG5))));
+
+	level = 0x80 | change;
+
+	PG_RETURN_BOOL(pg_msgmodule_internal(moduleid, fileid, msgid, level));
+}
+
+static bool
+pg_msgmodule_enable_disable(int32 pid, bool enable)
+{
+	BackendId backendId;
+	/*
+	 * pid == -1 implies the action is applied for all backends
+	 */
+	if (pid != -1)
+	{
+		volatile PGPROC *proc = BackendPidGetProc(pid);
+		if (proc == NULL)
+			ereport(ERROR,
+					(errcode(ERRCODE_INTERNAL_ERROR),
+					 (errmsg("PID %d is not a PostgreSQL server process", pid))));
+		backendId = proc->backendId;
+		MsgModuleCtl->mm_flags[StartOfBackendFlags + backendId] = enable ? true :
+			false;
+	}
+	else
+	{
+		/*
+		 * All backends should not honour the current settings
+		 */
+		memset(MsgModuleCtl->mm_flags + StartOfBackendFlags, true,
+				MaxBackends);
+	}
+
+	/*
+	 * If we are disabling the last backend and no new backends are going to
+	 * participate in the facility, then just disable the entire facility so
+	 * that subsequent backends can quickly bail out
+	 *
+	 * XXX There is a race possible here if another call to turn on the logging
+	 * comes just after we had passed over tje slot. We should possibly protect
+	 * access to the shared memory, but doesn't seem like worth the effort
+	 * right now
+	 */
+	if (!enable && !MsgModuleCtl->mm_persistent)
+	{
+		int i;
+		for (i = 0; i < MaxBackends; i++)
+			if (MsgModuleCtl->mm_flags[StartOfBackendFlags + i])
+				break;
+		if (i == MaxBackends)
+			MsgModuleCtl->mm_enabled = false;
+	}
+	else
+		MsgModuleCtl->mm_enabled = true;
+
+	return true;
+}
+
+Datum
+pg_msgmodule_enable(PG_FUNCTION_ARGS)
+{
+	int32 pid = PG_GETARG_INT32(0);
+
+	if (!superuser())
+		ereport(ERROR,
+				(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
+			 (errmsg("must be superuser to change elog message level"))));
+
+	PG_RETURN_BOOL(pg_msgmodule_enable_disable(pid, true));
+}
+
+Datum
+pg_msgmodule_disable(PG_FUNCTION_ARGS)
+{
+	int32 pid = PG_GETARG_INT32(0);
+
+	if (!superuser())
+		ereport(ERROR,
+				(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
+			 (errmsg("must be superuser to change elog message level"))));
+
+	PG_RETURN_BOOL(pg_msgmodule_enable_disable(pid, false));
+}
+
+/*
+ * pg_msgmodule_enable_all(bool persistent)
+ *
+ * All processes to start honouring the current settings of overridden log
+ * levels. If "persistent" is set to true, then all future processes will also
+ * honour the settings.
+ */
+Datum
+pg_msgmodule_enable_all(PG_FUNCTION_ARGS)
+{
+	bool persistent = PG_GETARG_BOOL(0);
+
+	if (!superuser())
+		ereport(ERROR,
+				(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
+			 (errmsg("must be superuser to change elog message level"))));
+
+	MsgModuleCtl->mm_persistent = persistent;
+	if (persistent)
+	{
+		MsgModuleCtl->mm_enabled = true;
+		memset(MsgModuleCtl->mm_flags + StartOfBackendFlags, true,
+				MaxBackends);
+		PG_RETURN_BOOL(true);
+	}
+	else
+		PG_RETURN_BOOL(pg_msgmodule_enable_disable(-1, true));
+}
+
+/*
+ * Disable all current and future processes from honouring the overridden log
+ * levels
+ */
+Datum
+pg_msgmodule_disable_all(PG_FUNCTION_ARGS)
+{
+	if (!superuser())
+		ereport(ERROR,
+				(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
+			 (errmsg("must be superuser to change elog message level"))));
+
+	MsgModuleCtl->mm_enabled = false;
+	MsgModuleCtl->mm_persistent = false;
+	memset(MsgModuleCtl->mm_flags + StartOfBackendFlags, false,
+			MaxBackends);
+	PG_RETURN_BOOL(true);
+}
+
+/*
+ * Handle proc exit. If persistent flag is not set then also check if we are
+ * the last process using the facility and if so, disable it. The current log
+ * settings are retained and will be used when newer processes are enabled for
+ * the facility
+ */
+static void
+AtProcExit_MsgModule(int code, Datum arg)
+{
+	MsgModuleCtl->mm_flags[StartOfBackendFlags + MyBackendId] = false;
+	if (!MsgModuleCtl->mm_persistent)
+	{
+		int i;
+		for (i = 0; i < MaxBackends; i++)
+			if (MsgModuleCtl->mm_flags[StartOfBackendFlags + i])
+				break;
+		if (i == MaxBackends)
+			MsgModuleCtl->mm_enabled = false;
+	}
+}
+#else
+Datum
+pg_msgmodule_set(PG_FUNCTION_ARGS)
+{
+	ereport(ERROR, (errmsg_internal("Module msgid support not available. "
+					"Please recompile with --enable-genmsgids")));
+}
+Datum
+pg_msgmodule_change(PG_FUNCTION_ARGS)
+{
+	ereport(ERROR, (errmsg_internal("Module msgid support not available. "
+					"Please recompile with --enable-genmsgids")));
+}
+Datum
+pg_msgmodule_enable(PG_FUNCTION_ARGS)
+{
+	ereport(ERROR, (errmsg_internal("Module msgid support not available. "
+					"Please recompile with --enable-genmsgids")));
+}
+Datum
+pg_msgmodule_disable(PG_FUNCTION_ARGS)
+{
+	ereport(ERROR, (errmsg_internal("Module msgid support not available. "
+					"Please recompile with --enable-genmsgids")));
+}
+Datum
+pg_msgmodule_enable_all(PG_FUNCTION_ARGS)
+{
+	ereport(ERROR, (errmsg_internal("Module msgid support not available. "
+					"Please recompile with --enable-genmsgids")));
+}
+Datum
+pg_msgmodule_disable_all(PG_FUNCTION_ARGS)
+{
+	ereport(ERROR, (errmsg_internal("Module msgid support not available. "
+					"Please recompile with --enable-genmsgids")));
+}
+#endif
diff --git a/src/common/Makefile b/src/common/Makefile
index 72b7369..84735f3 100644
--- a/src/common/Makefile
+++ b/src/common/Makefile
@@ -74,8 +74,15 @@ libpgcommon_srv.a: $(OBJS_SRV)
 # their *.o siblings as well, which do have proper dependencies.  It's
 # a hack that might fail someday if there is a *_srv.o without a
 # corresponding *.o, but it works for now.
+ifeq ($(genmsgids), yes)
+PGXL_MSG_FILEID := 1
+%_srv.o: %.c %.o
+	$(CC) $(CFLAGS) -DPGXL_MSG_MODULE=$(PGXL_MSG_MODULE) -DPGXL_MSG_FILEID=$(PGXL_MSG_FILEID) $(subst -DFRONTEND,, $(CPPFLAGS)) -c $< -o $@
+	$(eval PGXL_MSG_FILEID := $(shell expr $(PGXL_MSG_FILEID) + 1))
+else
 %_srv.o: %.c %.o
 	$(CC) $(CFLAGS) $(subst -DFRONTEND ,, $(CPPFLAGS)) -c $< -o $@
+endif
 
 $(OBJS_SRV): | submake-errcodes
 
diff --git a/src/include/catalog/pg_proc.h b/src/include/catalog/pg_proc.h
index e2d08ba..e41f1fe 100644
--- a/src/include/catalog/pg_proc.h
+++ b/src/include/catalog/pg_proc.h
@@ -5344,6 +5344,21 @@ DESCR("pg_controldata recovery state information as a function");
 DATA(insert OID = 3444 ( pg_control_init PGNSP PGUID 12 1 0 0 0 f f f f t f v s 0 0 2249 "" "{23,23,23,23,23,23,23,23,23,16,16,16,23}" "{o,o,o,o,o,o,o,o,o,o,o,o,o}" "{max_data_alignment,database_block_size,blocks_per_segment,wal_block_size,bytes_per_wal_segment,max_identifier_length,max_index_columns,max_toast_chunk_size,large_object_chunk_size,bigint_timestamps,float4_pass_by_value,float8_pass_by_value,data_page_checksum_version}" _null_ _null_ pg_control_init _null_ _null_ _null_ ));
 DESCR("pg_controldata init state information as a function");
 
+#ifdef USE_MODULE_MSGIDS
+DATA(insert OID = 6015 ( pg_msgmodule_set PGNSP PGUID 12 1 1 0 0 f f f f t t i s 4 0 16 "20 20 20 2275" _null_ _null_ _null_ _null_ _null_ pg_msgmodule_set _null_ _null_ _null_ ));
+DESCR("set debugging level for module/file/msg");
+DATA(insert OID = 6016 ( pg_msgmodule_change PGNSP PGUID 12 1 1 0 0 f f f f t t i s 4 0 16 "20 20 20 20" _null_ _null_ _null_ _null_ _null_ pg_msgmodule_change _null_ _null_ _null_ ));
+DESCR("change debugging level for module/file/msg");
+DATA(insert OID = 6017 ( pg_msgmodule_enable PGNSP PGUID 12 1 1 0 0 f f f f t t i s 1 0 16 "20" _null_ _null_ _null_ _null_ _null_ pg_msgmodule_enable _null_ _null_ _null_ ));
+DESCR("pid to honour overriden log levels");
+DATA(insert OID = 6018 ( pg_msgmodule_disable PGNSP PGUID 12 1 1 0 0 f f f f t t i s 1 0 16 "20" _null_ _null_ _null_ _null_ _null_ pg_msgmodule_disable _null_ _null_ _null_ ));
+DESCR("pid to ignore overriden log levels");
+DATA(insert OID = 6019 ( pg_msgmodule_enable_all PGNSP PGUID 12 1 1 0 0 f f f f t t i s 1 0 16 "16" _null_ _null_ _null_ _null_ _null_ pg_msgmodule_enable_all _null_ _null_ _null_ ));
+DESCR("all current/future processes to honour overriden log levels");
+DATA(insert OID = 6020 ( pg_msgmodule_disable_all PGNSP PGUID 12 1 1 0 0 f f f f t t i s 0 0 16 "" _null_ _null_ _null_ _null_ _null_ pg_msgmodule_disable_all _null_ _null_ _null_ ));
+DESCR("all processes to ignore overriden log levels");
+#endif
+
 /*
  * Symbolic values for provolatile column: these indicate whether the result
  * of a function is dependent *only* on the values of its explicit arguments,
diff --git a/src/include/pg_config.h.in b/src/include/pg_config.h.in
index b621ff2..b5f88db 100644
--- a/src/include/pg_config.h.in
+++ b/src/include/pg_config.h.in
@@ -790,6 +790,9 @@
 /* Define to 1 to build with assertion checks. (--enable-cassert) */
 #undef USE_ASSERT_CHECKING
 
+/* Define to 1 to build with module msgids. (--enable-genmsgids) */
+#undef USE_MODULE_MSGIDS
+
 /* Define to 1 to build with Bonjour support. (--with-bonjour) */
 #undef USE_BONJOUR
 
diff --git a/src/include/utils/builtins.h b/src/include/utils/builtins.h
index 2ae212a..50bc8db 100644
--- a/src/include/utils/builtins.h
+++ b/src/include/utils/builtins.h
@@ -1332,4 +1332,12 @@ extern Datum pg_prepared_statement(PG_FUNCTION_ARGS);
 /* utils/mmgr/portalmem.c */
 extern Datum pg_cursor(PG_FUNCTION_ARGS);
 
+#ifdef USE_MODULE_MSGIDS
+extern Datum pg_msgmodule_set(PG_FUNCTION_ARGS);
+extern Datum pg_msgmodule_change(PG_FUNCTION_ARGS);
+extern Datum pg_msgmodule_enable(PG_FUNCTION_ARGS);
+extern Datum pg_msgmodule_disable(PG_FUNCTION_ARGS);
+extern Datum pg_msgmodule_enable_all(PG_FUNCTION_ARGS);
+extern Datum pg_msgmodule_disable_all(PG_FUNCTION_ARGS);
+#endif
 #endif   /* BUILTINS_H */
diff --git a/src/include/utils/elog.h b/src/include/utils/elog.h
index f4ff03e..fe2dd50 100644
--- a/src/include/utils/elog.h
+++ b/src/include/utils/elog.h
@@ -100,6 +100,26 @@
  * prevents gcc from making the unreachability deduction at optlevel -O0.
  *----------
  */
+#ifdef USE_MODULE_MSGIDS
+#ifdef HAVE__BUILTIN_CONSTANT_P
+#define ereport_domain(elevel, domain, rest)	\
+	do { \
+		if (errstart(elevel, __FILE__, __LINE__, PGXL_MSG_MODULE, PGXL_MSG_FILEID, __COUNTER__, PG_FUNCNAME_MACRO, domain)) \
+			errfinish rest; \
+		if (__builtin_constant_p(elevel) && (elevel) >= ERROR) \
+			pg_unreachable(); \
+	} while(0)
+#else							/* !HAVE__BUILTIN_CONSTANT_P */
+#define ereport_domain(elevel, domain, rest)	\
+	do { \
+		const int elevel_ = (elevel); \
+		if (errstart(elevel, __FILE__, __LINE__, PGXL_MSG_MODULE, PGXL_MSG_FILEID, __COUNTER__, PG_FUNCNAME_MACRO, domain)) \
+			errfinish rest; \
+		if (elevel_ >= ERROR) \
+			pg_unreachable(); \
+	} while(0)
+#endif   /* HAVE__BUILTIN_CONSTANT_P */
+#else
 #ifdef HAVE__BUILTIN_CONSTANT_P
 #define ereport_domain(elevel, domain, rest)	\
 	do { \
@@ -112,12 +132,13 @@
 #define ereport_domain(elevel, domain, rest)	\
 	do { \
 		const int elevel_ = (elevel); \
-		if (errstart(elevel_, __FILE__, __LINE__, PG_FUNCNAME_MACRO, domain)) \
+		if (errstart(elevel, __FILE__, __LINE__, PG_FUNCNAME_MACRO, domain)) \
 			errfinish rest; \
 		if (elevel_ >= ERROR) \
 			pg_unreachable(); \
 	} while(0)
 #endif   /* HAVE__BUILTIN_CONSTANT_P */
+#endif
 
 #define ereport(elevel, rest)	\
 	ereport_domain(elevel, TEXTDOMAIN, rest)
@@ -125,7 +146,11 @@
 #define TEXTDOMAIN NULL
 
 extern bool errstart(int elevel, const char *filename, int lineno,
-		 const char *funcname, const char *domain);
+#ifdef USE_MODULE_MSGIDS
+		 int moduleid, int fileid, int msgid,
+#endif
+		 const char *funcname, const char *domain
+		 );
 extern void errfinish(int dummy,...);
 
 extern int	errcode(int sqlerrcode);
@@ -188,6 +213,7 @@ extern int	getinternalerrposition(void);
  *		elog(ERROR, "portal \"%s\" not found", stmt->portalname);
  *----------
  */
+#ifdef USE_MODULE_MSGIDS
 #ifdef HAVE__VA_ARGS
 /*
  * If we have variadic macros, we can give the compiler a hint about the
@@ -198,6 +224,34 @@ extern int	getinternalerrposition(void);
 #ifdef HAVE__BUILTIN_CONSTANT_P
 #define elog(elevel, ...)  \
 	do { \
+		elog_start(__FILE__, __LINE__, PGXL_MSG_MODULE, PGXL_MSG_FILEID, __COUNTER__, PG_FUNCNAME_MACRO); \
+		elog_finish(elevel, __VA_ARGS__); \
+		if (__builtin_constant_p(elevel) && (elevel) >= ERROR) \
+			pg_unreachable(); \
+	} while(0)
+#else							/* !HAVE__BUILTIN_CONSTANT_P */
+#define elog(elevel, ...)  \
+	do { \
+		int		elevel_; \
+		elog_start(__FILE__, __LINE__, PGXL_MSG_MODULE, PGXL_MSG_FILEID, __COUNTER__, PG_FUNCNAME_MACRO); \
+		elevel_ = (elevel); \
+		elog_finish(elevel_, __VA_ARGS__); \
+		if (elevel_ >= ERROR) \
+			pg_unreachable(); \
+	} while(0)
+#endif   /* HAVE__BUILTIN_CONSTANT_P */
+#else							/* !HAVE__VA_ARGS */
+#define elog  \
+	do { \
+		elog_start(__FILE__, __LINE__, PGXL_MSG_MODULE, PGXL_MSG_FILEID, __COUNTER__, PG_FUNCNAME_MACRO); \
+	} while (0); \
+	elog_finish
+#endif   /* HAVE__VA_ARGS */
+#else
+#ifdef HAVE__VA_ARGS
+#ifdef HAVE__BUILTIN_CONSTANT_P
+#define elog(elevel, ...)  \
+	do { \
 		elog_start(__FILE__, __LINE__, PG_FUNCNAME_MACRO); \
 		elog_finish(elevel, __VA_ARGS__); \
 		if (__builtin_constant_p(elevel) && (elevel) >= ERROR) \
@@ -216,11 +270,19 @@ extern int	getinternalerrposition(void);
 #endif   /* HAVE__BUILTIN_CONSTANT_P */
 #else							/* !HAVE__VA_ARGS */
 #define elog  \
-	elog_start(__FILE__, __LINE__, PG_FUNCNAME_MACRO), \
+	do { \
+		elog_start(__FILE__, __LINE__, PG_FUNCNAME_MACRO); \
+	} while (0); \
 	elog_finish
 #endif   /* HAVE__VA_ARGS */
+#endif
 
-extern void elog_start(const char *filename, int lineno, const char *funcname);
+extern void elog_start(const char *filename, int lineno,
+#ifdef USE_MODULE_MSGIDS
+		int moduleid, int flieid, int msgid,
+#endif
+		const char *funcname
+		);
 extern void elog_finish(int elevel, const char *fmt,...) pg_attribute_printf(2, 3);
 
 
@@ -354,11 +416,26 @@ typedef struct ErrorData
 	int			internalpos;	/* cursor index into internalquery */
 	char	   *internalquery;	/* text of internally-generated query */
 	int			saved_errno;	/* errno at entry */
+#ifdef USE_MODULE_MSGIDS
+	int			moduleid;
+	int			fileid;
+	int			msgid;			/* msgid */
+#endif
 
 	/* context containing associated non-constant strings */
 	struct MemoryContextData *assoc_context;
 } ErrorData;
 
+#ifdef USE_MODULE_MSGIDS
+#define PGXL_MSG_MAX_MODULES			256
+#define PGXL_MSG_MAX_FILEIDS_PER_MODULE	100
+#define PGXL_MSG_MAX_MSGIDS_PER_FILE	300
+
+extern Size MsgModuleShmemSize(void);
+extern void MsgModuleShmemInit(void);
+extern void AtProcStart_MsgModule(void);
+#endif
+
 extern void EmitErrorReport(void);
 extern ErrorData *CopyErrorData(void);
 extern void FreeErrorData(ErrorData *edata);
diff --git a/src/port/Makefile b/src/port/Makefile
index bc9b63a..2aca390 100644
--- a/src/port/Makefile
+++ b/src/port/Makefile
@@ -76,8 +76,15 @@ libpgport_srv.a: $(OBJS_SRV)
 # a hack that might fail someday if there is a *_srv.o without a
 # corresponding *.o, but it works for now (and those would probably go
 # into src/backend/port/ anyway).
+ifeq ($(genmsgids), yes)
+PGXL_MSG_FILEID := 1
+%_srv.o: %.c %.o
+	$(CC) $(CFLAGS) -DPGXL_MSG_MODULE=$(PGXL_MSG_MODULE) -DPGXL_MSG_FILEID=$(PGXL_MSG_FILEID) $(subst -DFRONTEND,, $(CPPFLAGS)) -c $< -o $@
+	$(eval PGXL_MSG_FILEID := $(shell expr $(PGXL_MSG_FILEID) + 1))
+else
 %_srv.o: %.c %.o
 	$(CC) $(CFLAGS) $(subst -DFRONTEND,, $(CPPFLAGS)) -c $< -o $@
+endif
 
 $(OBJS_SRV): | submake-errcodes