Generate less WAL during GiST, GIN and SP-GiST index build.

Instead of WAL-logging every modification during the build separately,
first build the index without any WAL-logging, and make a separate pass
through the index at the end, to write all pages to the WAL. This
significantly reduces the amount of WAL generated, and is usually also
faster, despite the extra I/O needed for the extra scan through the index.
WAL generated this way is also faster to replay.

For GiST, the LSN-NSN interlock makes this a little tricky. All pages must
be marked with a valid (i.e. non-zero) LSN, so that the parent-child
LSN-NSN interlock works correctly. We now use magic value 1 for that during
index build. Change the fake LSN counter to begin from 1000, so that 1 is
safely smaller than any real or fake LSN. 2 would've been enough for our
purposes, but let's reserve a bigger range, in case we need more special
values in the future.

Author: Anastasia Lubennikova, Andrey V. Lepikhov
Reviewed-by: Heikki Linnakangas, Dmitry Dolgov

7 files changed, 25 insertions, 62 deletions

diff --git a/src/backend/access/gin/ginbtree.c b/src/backend/access/gin/ginbtree.c
index 533949e46a4..9f82eef8c39 100644
--- a/src/backend/access/gin/ginbtree.c
+++ b/src/backend/access/gin/ginbtree.c
@@ -396,7 +396,7 @@ ginPlaceToPage(GinBtree btree, GinBtreeStack *stack,
 		/* It will fit, perform the insertion */
 		START_CRIT_SECTION();
 
-		if (RelationNeedsWAL(btree->index))
+		if (RelationNeedsWAL(btree->index) && !btree->isBuild)
 		{
 			XLogBeginInsert();
 			XLogRegisterBuffer(0, stack->buffer, REGBUF_STANDARD);
@@ -417,7 +417,7 @@ ginPlaceToPage(GinBtree btree, GinBtreeStack *stack,
 			MarkBufferDirty(childbuf);
 		}
 
-		if (RelationNeedsWAL(btree->index))
+		if (RelationNeedsWAL(btree->index) && !btree->isBuild)
 		{
 			XLogRecPtr	recptr;
 			ginxlogInsert xlrec;
@@ -595,7 +595,7 @@ ginPlaceToPage(GinBtree btree, GinBtreeStack *stack,
 		}
 
 		/* write WAL record */
-		if (RelationNeedsWAL(btree->index))
+		if (RelationNeedsWAL(btree->index) && !btree->isBuild)
 		{
 			XLogRecPtr	recptr;
 
diff --git a/src/backend/access/gin/gindatapage.c b/src/backend/access/gin/gindatapage.c
index 3ad8b767102..fb085c7dd84 100644
--- a/src/backend/access/gin/gindatapage.c
+++ b/src/backend/access/gin/gindatapage.c
@@ -593,7 +593,7 @@ dataBeginPlaceToPageLeaf(GinBtree btree, Buffer buf, GinBtreeStack *stack,
 		 * Great, all the items fit on a single page.  If needed, prepare data
 		 * for a WAL record describing the changes we'll make.
 		 */
-		if (RelationNeedsWAL(btree->index))
+		if (RelationNeedsWAL(btree->index) && !btree->isBuild)
 			computeLeafRecompressWALData(leaf);
 
 		/*
@@ -719,7 +719,7 @@ dataExecPlaceToPageLeaf(GinBtree btree, Buffer buf, GinBtreeStack *stack,
 	dataPlaceToPageLeafRecompress(buf, leaf);
 
 	/* If needed, register WAL data built by computeLeafRecompressWALData */
-	if (RelationNeedsWAL(btree->index))
+	if (RelationNeedsWAL(btree->index) && !btree->isBuild)
 	{
 		XLogRegisterBufData(0, leaf->walinfo, leaf->walinfolen);
 	}
@@ -1152,7 +1152,7 @@ dataExecPlaceToPageInternal(GinBtree btree, Buffer buf, GinBtreeStack *stack,
 	pitem = (PostingItem *) insertdata;
 	GinDataPageAddPostingItem(page, pitem, off);
 
-	if (RelationNeedsWAL(btree->index))
+	if (RelationNeedsWAL(btree->index) && !btree->isBuild)
 	{
 		/*
 		 * This must be static, because it has to survive until XLogInsert,
@@ -1773,6 +1773,7 @@ createPostingTree(Relation index, ItemPointerData *items, uint32 nitems,
 	Pointer		ptr;
 	int			nrootitems;
 	int			rootsize;
+	bool		is_build = (buildStats != NULL);
 
 	/* Construct the new root page in memory first. */
 	tmppage = (Page) palloc(BLCKSZ);
@@ -1826,7 +1827,7 @@ createPostingTree(Relation index, ItemPointerData *items, uint32 nitems,
 	PageRestoreTempPage(tmppage, page);
 	MarkBufferDirty(buffer);
 
-	if (RelationNeedsWAL(index))
+	if (RelationNeedsWAL(index) && !is_build)
 	{
 		XLogRecPtr	recptr;
 		ginxlogCreatePostingTree data;
diff --git a/src/backend/access/gin/ginentrypage.c b/src/backend/access/gin/ginentrypage.c
index 4889de2a4f5..1f5ba33d512 100644
--- a/src/backend/access/gin/ginentrypage.c
+++ b/src/backend/access/gin/ginentrypage.c
@@ -571,7 +571,7 @@ entryExecPlaceToPage(GinBtree btree, Buffer buf, GinBtreeStack *stack,
 		elog(ERROR, "failed to add item to index page in \"%s\"",
 			 RelationGetRelationName(btree->index));
 
-	if (RelationNeedsWAL(btree->index))
+	if (RelationNeedsWAL(btree->index) && !btree->isBuild)
 	{
 		/*
 		 * This must be static, because it has to survive until XLogInsert,
diff --git a/src/backend/access/gin/gininsert.c b/src/backend/access/gin/gininsert.c
index edc353a7fe0..55eab146173 100644
--- a/src/backend/access/gin/gininsert.c
+++ b/src/backend/access/gin/gininsert.c
@@ -195,6 +195,7 @@ ginEntryInsert(GinState *ginstate,
 		buildStats->nEntries++;
 
 	ginPrepareEntryScan(&btree, attnum, key, category, ginstate);
+	btree.isBuild = (buildStats != NULL);
 
 	stack = ginFindLeafPage(&btree, false, false, NULL);
 	page = BufferGetPage(stack->buffer);
@@ -347,23 +348,6 @@ ginbuild(Relation heap, Relation index, IndexInfo *indexInfo)
 	GinInitBuffer(RootBuffer, GIN_LEAF);
 	MarkBufferDirty(RootBuffer);
 
-	if (RelationNeedsWAL(index))
-	{
-		XLogRecPtr	recptr;
-		Page		page;
-
-		XLogBeginInsert();
-		XLogRegisterBuffer(0, MetaBuffer, REGBUF_WILL_INIT | REGBUF_STANDARD);
-		XLogRegisterBuffer(1, RootBuffer, REGBUF_WILL_INIT);
-
-		recptr = XLogInsert(RM_GIN_ID, XLOG_GIN_CREATE_INDEX);
-
-		page = BufferGetPage(RootBuffer);
-		PageSetLSN(page, recptr);
-
-		page = BufferGetPage(MetaBuffer);
-		PageSetLSN(page, recptr);
-	}
 
 	UnlockReleaseBuffer(MetaBuffer);
 	UnlockReleaseBuffer(RootBuffer);
@@ -419,7 +403,18 @@ ginbuild(Relation heap, Relation index, IndexInfo *indexInfo)
 	 * Update metapage stats
 	 */
 	buildstate.buildStats.nTotalPages = RelationGetNumberOfBlocks(index);
-	ginUpdateStats(index, &buildstate.buildStats);
+	ginUpdateStats(index, &buildstate.buildStats, true);
+
+	/*
+	 * We didn't write WAL records as we built the index, so if WAL-logging is
+	 * required, write all pages to the WAL now.
+	 */
+	if (RelationNeedsWAL(index))
+	{
+		log_newpage_range(index, MAIN_FORKNUM,
+						  0, RelationGetNumberOfBlocks(index),
+						  true);
+	}
 
 	/*
 	 * Return statistics
diff --git a/src/backend/access/gin/ginutil.c b/src/backend/access/gin/ginutil.c
index d2360eeafb0..cf9699ad18e 100644
--- a/src/backend/access/gin/ginutil.c
+++ b/src/backend/access/gin/ginutil.c
@@ -662,7 +662,7 @@ ginGetStats(Relation index, GinStatsData *stats)
  * Note: nPendingPages and ginVersion are *not* copied over
  */
 void
-ginUpdateStats(Relation index, const GinStatsData *stats)
+ginUpdateStats(Relation index, const GinStatsData *stats, bool is_build)
 {
 	Buffer		metabuffer;
 	Page		metapage;
@@ -692,7 +692,7 @@ ginUpdateStats(Relation index, const GinStatsData *stats)
 
 	MarkBufferDirty(metabuffer);
 
-	if (RelationNeedsWAL(index))
+	if (RelationNeedsWAL(index) && !is_build)
 	{
 		XLogRecPtr	recptr;
 		ginxlogUpdateMeta data;
diff --git a/src/backend/access/gin/ginvacuum.c b/src/backend/access/gin/ginvacuum.c
index dfe885b1017..b9a28d18633 100644
--- a/src/backend/access/gin/ginvacuum.c
+++ b/src/backend/access/gin/ginvacuum.c
@@ -759,7 +759,7 @@ ginvacuumcleanup(IndexVacuumInfo *info, IndexBulkDeleteResult *stats)
 
 	/* Update the metapage with accurate page and entry counts */
 	idxStat.nTotalPages = npages;
-	ginUpdateStats(info->index, &idxStat);
+	ginUpdateStats(info->index, &idxStat, false);
 
 	/* Finally, vacuum the FSM */
 	IndexFreeSpaceMapVacuum(info->index);
diff --git a/src/backend/access/gin/ginxlog.c b/src/backend/access/gin/ginxlog.c
index c467ffa346d..b648af1ff65 100644
--- a/src/backend/access/gin/ginxlog.c
+++ b/src/backend/access/gin/ginxlog.c
@@ -41,36 +41,6 @@ ginRedoClearIncompleteSplit(XLogReaderState *record, uint8 block_id)
 }
 
 static void
-ginRedoCreateIndex(XLogReaderState *record)
-{
-	XLogRecPtr	lsn = record->EndRecPtr;
-	Buffer		RootBuffer,
-				MetaBuffer;
-	Page		page;
-
-	MetaBuffer = XLogInitBufferForRedo(record, 0);
-	Assert(BufferGetBlockNumber(MetaBuffer) == GIN_METAPAGE_BLKNO);
-	page = (Page) BufferGetPage(MetaBuffer);
-
-	GinInitMetabuffer(MetaBuffer);
-
-	PageSetLSN(page, lsn);
-	MarkBufferDirty(MetaBuffer);
-
-	RootBuffer = XLogInitBufferForRedo(record, 1);
-	Assert(BufferGetBlockNumber(RootBuffer) == GIN_ROOT_BLKNO);
-	page = (Page) BufferGetPage(RootBuffer);
-
-	GinInitBuffer(RootBuffer, GIN_LEAF);
-
-	PageSetLSN(page, lsn);
-	MarkBufferDirty(RootBuffer);
-
-	UnlockReleaseBuffer(RootBuffer);
-	UnlockReleaseBuffer(MetaBuffer);
-}
-
-static void
 ginRedoCreatePTree(XLogReaderState *record)
 {
 	XLogRecPtr	lsn = record->EndRecPtr;
@@ -767,9 +737,6 @@ gin_redo(XLogReaderState *record)
 	oldCtx = MemoryContextSwitchTo(opCtx);
 	switch (info)
 	{
-		case XLOG_GIN_CREATE_INDEX:
-			ginRedoCreateIndex(record);
-			break;
 		case XLOG_GIN_CREATE_PTREE:
 			ginRedoCreatePTree(record);
 			break;