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

1 files changed, 0 insertions, 35 deletions

diff --git a/src/backend/access/spgist/spgxlog.c b/src/backend/access/spgist/spgxlog.c
index 71836ee8a5b..ebe6ae8715b 100644
--- a/src/backend/access/spgist/spgxlog.c
+++ b/src/backend/access/spgist/spgxlog.c
@@ -73,38 +73,6 @@ addOrReplaceTuple(Page page, Item tuple, int size, OffsetNumber offset)
 }
 
 static void
-spgRedoCreateIndex(XLogReaderState *record)
-{
-	XLogRecPtr	lsn = record->EndRecPtr;
-	Buffer		buffer;
-	Page		page;
-
-	buffer = XLogInitBufferForRedo(record, 0);
-	Assert(BufferGetBlockNumber(buffer) == SPGIST_METAPAGE_BLKNO);
-	page = (Page) BufferGetPage(buffer);
-	SpGistInitMetapage(page);
-	PageSetLSN(page, lsn);
-	MarkBufferDirty(buffer);
-	UnlockReleaseBuffer(buffer);
-
-	buffer = XLogInitBufferForRedo(record, 1);
-	Assert(BufferGetBlockNumber(buffer) == SPGIST_ROOT_BLKNO);
-	SpGistInitBuffer(buffer, SPGIST_LEAF);
-	page = (Page) BufferGetPage(buffer);
-	PageSetLSN(page, lsn);
-	MarkBufferDirty(buffer);
-	UnlockReleaseBuffer(buffer);
-
-	buffer = XLogInitBufferForRedo(record, 2);
-	Assert(BufferGetBlockNumber(buffer) == SPGIST_NULL_BLKNO);
-	SpGistInitBuffer(buffer, SPGIST_LEAF | SPGIST_NULLS);
-	page = (Page) BufferGetPage(buffer);
-	PageSetLSN(page, lsn);
-	MarkBufferDirty(buffer);
-	UnlockReleaseBuffer(buffer);
-}
-
-static void
 spgRedoAddLeaf(XLogReaderState *record)
 {
 	XLogRecPtr	lsn = record->EndRecPtr;
@@ -976,9 +944,6 @@ spg_redo(XLogReaderState *record)
 	oldCxt = MemoryContextSwitchTo(opCtx);
 	switch (info)
 	{
-		case XLOG_SPGIST_CREATE_INDEX:
-			spgRedoCreateIndex(record);
-			break;
 		case XLOG_SPGIST_ADD_LEAF:
 			spgRedoAddLeaf(record);
 			break;