From 2edd0ada13b4749487d0f046191ef2bcf8b11ca3 Mon Sep 17 00:00:00 2001
From: "Andrey V. Lepikhov" <a.lepikhov@postgrespro.ru>
Date: Tue, 2 Apr 2019 09:42:59 +0500
Subject: [PATCH 1/4] Relation-into-WAL-function

---
 src/backend/access/transam/generic_xlog.c | 63 +++++++++++++++++++++++
 src/include/access/generic_xlog.h         |  3 ++
 2 files changed, 66 insertions(+)

diff --git a/src/backend/access/transam/generic_xlog.c b/src/backend/access/transam/generic_xlog.c
index 5b00b7275b..0d5025f78a 100644
--- a/src/backend/access/transam/generic_xlog.c
+++ b/src/backend/access/transam/generic_xlog.c
@@ -16,6 +16,7 @@
 #include "access/bufmask.h"
 #include "access/generic_xlog.h"
 #include "access/xlogutils.h"
+#include "catalog/pg_control.h"
 #include "miscadmin.h"
 #include "utils/memutils.h"
 
@@ -542,3 +543,65 @@ generic_mask(char *page, BlockNumber blkno)
 
 	mask_unused_space(page);
 }
+
+/*
+ * Function for WAL-logging all pages of a relation.
+ * Caller is responsible for locking the relation exclusively.
+ */
+void
+log_relation(Relation rel)
+{
+	BlockNumber 		blkno = 0;
+	BlockNumber 		nblocks;
+	Buffer				bufpack[XLR_MAX_BLOCK_ID];
+
+	CHECK_FOR_INTERRUPTS();
+
+	/*
+	 * Iterate over all index pages and WAL-logging it. Pages are grouping into
+	 * the packages before adding to a WAL-record. Zero pages are not logged.
+	 */
+	nblocks = RelationGetNumberOfBlocks(rel);
+	while (blkno < nblocks)
+	{
+		XLogRecPtr recptr;
+		int8 nbufs = 0;
+		int8 i;
+
+		/*
+		 * Assemble package of relation blocks. Try to combine the maximum
+		 * possible number of blocks in one record.
+		 */
+		while (nbufs < XLR_MAX_BLOCK_ID && blkno < nblocks)
+		{
+			Buffer buf = ReadBuffer(rel, blkno);
+
+			if (!PageIsNew(BufferGetPage(buf)))
+				bufpack[nbufs++] = buf;
+			else
+				ReleaseBuffer(buf);
+			blkno++;
+		}
+
+		XLogBeginInsert();
+		XLogEnsureRecordSpace(nbufs, 0);
+
+		START_CRIT_SECTION();
+		for (i = 0; i < nbufs; i++)
+		{
+			LockBuffer(bufpack[i], BUFFER_LOCK_EXCLUSIVE);
+			XLogRegisterBuffer(i, bufpack[i], REGBUF_FORCE_IMAGE | REGBUF_STANDARD);
+		}
+
+		recptr = XLogInsert(RM_XLOG_ID, XLOG_FPI);
+
+		for (i = 0; i < nbufs; i++)
+		{
+			Page page = BufferGetPage(bufpack[i]);
+			PageSetLSN(page, recptr);
+			MarkBufferDirty(bufpack[i]);
+			UnlockReleaseBuffer(bufpack[i]);
+		}
+		END_CRIT_SECTION();
+	}
+}
diff --git a/src/include/access/generic_xlog.h b/src/include/access/generic_xlog.h
index cb5b5b713a..8abfa486c7 100644
--- a/src/include/access/generic_xlog.h
+++ b/src/include/access/generic_xlog.h
@@ -42,4 +42,7 @@ extern const char *generic_identify(uint8 info);
 extern void generic_desc(StringInfo buf, XLogReaderState *record);
 extern void generic_mask(char *pagedata, BlockNumber blkno);
 
+/* other utils */
+extern void log_relation(Relation rel);
+
 #endif							/* GENERIC_XLOG_H */
-- 
2.17.1