From ccadf73163ca88bdaa74b8223d4dde05d17f550b Mon Sep 17 00:00:00 2001 From: Heikki Linnakangas Date: Wed, 23 Aug 2023 17:21:31 +0300 Subject: [PATCH] Use the buffer cache when initializing an unlogged index. Some of the ambuildempty functions used smgrwrite() directly, followed by smgrimmedsync(). A few small problems with that: Firstly, one is supposed to use smgrextend() when extending a relation, not smgrwrite(). It doesn't make much difference in production builds. smgrextend() updates the relation size cache, so you miss that, but that's harmless because we never use the cached relation size of an init fork. But if you compile with CHECK_WRITE_VS_EXTEND, you get an assertion failure. Secondly, the smgrwrite() calls were performed before WAL-logging, so the page image written to disk had 0/0 as the LSN, not the LSN of the WAL record. That's also harmless in practice, but seems sloppy. Thirdly, it's better to use the buffer cache, because then you don't need to smgrimmedsync() the relation to disk, which adds latency. Bypassing the cache makes sense for bulk operations like index creation, but not when you're just initializing an empty index. Creation of unlogged tables is hardly performance bottleneck in any real world applications, but nevertheless. Backpatch to v16, but no further. These issues should be harmless in practice, so better to not rock the boat in older branches. Reviewed-by: Robert Haas Discussion: https://www.postgresql.org/message-id/6e5bbc08-cdfc-b2b3-9e23-1a914b9850a9@iki.fi --- contrib/bloom/blinsert.c | 29 ++---------- contrib/bloom/bloom.h | 2 +- contrib/bloom/blutils.c | 8 ++-- src/backend/access/nbtree/nbtree.c | 41 ++++++++--------- src/backend/access/spgist/spginsert.c | 63 ++++++++++++--------------- 5 files changed, 58 insertions(+), 85 deletions(-) diff --git a/contrib/bloom/blinsert.c b/contrib/bloom/blinsert.c index b42b9e6c41..b90145148d 100644 --- a/contrib/bloom/blinsert.c +++ b/contrib/bloom/blinsert.c @@ -129,7 +129,7 @@ blbuild(Relation heap, Relation index, IndexInfo *indexInfo) RelationGetRelationName(index)); /* Initialize the meta page */ - BloomInitMetapage(index); + BloomInitMetapage(index, MAIN_FORKNUM); /* Initialize the bloom build state */ memset(&buildstate, 0, sizeof(buildstate)); @@ -163,31 +163,8 @@ blbuild(Relation heap, Relation index, IndexInfo *indexInfo) void blbuildempty(Relation index) { - Page metapage; - - /* Construct metapage. */ - metapage = (Page) palloc_aligned(BLCKSZ, PG_IO_ALIGN_SIZE, 0); - BloomFillMetapage(index, metapage); - - /* - * Write the page and log it. It might seem that an immediate sync would - * be sufficient to guarantee that the file exists on disk, but recovery - * itself might remove it while replaying, for example, an - * XLOG_DBASE_CREATE* or XLOG_TBLSPC_CREATE record. Therefore, we need - * this even when wal_level=minimal. - */ - PageSetChecksumInplace(metapage, BLOOM_METAPAGE_BLKNO); - smgrwrite(RelationGetSmgr(index), INIT_FORKNUM, BLOOM_METAPAGE_BLKNO, - metapage, true); - log_newpage(&(RelationGetSmgr(index))->smgr_rlocator.locator, INIT_FORKNUM, - BLOOM_METAPAGE_BLKNO, metapage, true); - - /* - * An immediate sync is required even if we xlog'd the page, because the - * write did not go through shared_buffers and therefore a concurrent - * checkpoint may have moved the redo pointer past our xlog record. - */ - smgrimmedsync(RelationGetSmgr(index), INIT_FORKNUM); + /* Initialize the meta page */ + BloomInitMetapage(index, INIT_FORKNUM); } /* diff --git a/contrib/bloom/bloom.h b/contrib/bloom/bloom.h index efdf9415d1..330811ec60 100644 --- a/contrib/bloom/bloom.h +++ b/contrib/bloom/bloom.h @@ -177,7 +177,7 @@ typedef BloomScanOpaqueData *BloomScanOpaque; /* blutils.c */ extern void initBloomState(BloomState *state, Relation index); extern void BloomFillMetapage(Relation index, Page metaPage); -extern void BloomInitMetapage(Relation index); +extern void BloomInitMetapage(Relation index, ForkNumber forknum); extern void BloomInitPage(Page page, uint16 flags); extern Buffer BloomNewBuffer(Relation index); extern void signValue(BloomState *state, BloomSignatureWord *sign, Datum value, int attno); diff --git a/contrib/bloom/blutils.c b/contrib/bloom/blutils.c index a017d58bbe..f23fbb1d9e 100644 --- a/contrib/bloom/blutils.c +++ b/contrib/bloom/blutils.c @@ -443,7 +443,7 @@ BloomFillMetapage(Relation index, Page metaPage) * Initialize metapage for bloom index. */ void -BloomInitMetapage(Relation index) +BloomInitMetapage(Relation index, ForkNumber forknum) { Buffer metaBuffer; Page metaPage; @@ -451,9 +451,11 @@ BloomInitMetapage(Relation index) /* * Make a new page; since it is first page it should be associated with - * block number 0 (BLOOM_METAPAGE_BLKNO). + * block number 0 (BLOOM_METAPAGE_BLKNO). No need to hold the extension + * lock because there cannot be concurrent inserters yet. */ - metaBuffer = BloomNewBuffer(index); + metaBuffer = ReadBufferExtended(index, forknum, P_NEW, RBM_NORMAL, NULL); + LockBuffer(metaBuffer, BUFFER_LOCK_EXCLUSIVE); Assert(BufferGetBlockNumber(metaBuffer) == BLOOM_METAPAGE_BLKNO); /* Initialize contents of meta page */ diff --git a/src/backend/access/nbtree/nbtree.c b/src/backend/access/nbtree/nbtree.c index 4553aaee53..ad07b80f75 100644 --- a/src/backend/access/nbtree/nbtree.c +++ b/src/backend/access/nbtree/nbtree.c @@ -151,31 +151,32 @@ bthandler(PG_FUNCTION_ARGS) void btbuildempty(Relation index) { + Buffer metabuf; Page metapage; - /* Construct metapage. */ - metapage = (Page) palloc_aligned(BLCKSZ, PG_IO_ALIGN_SIZE, 0); + /* + * Initalize the metapage. + * + * Regular index build bypasses the buffer manager and uses smgr functions + * directly, with an smgrimmedsync() call at the end. That makes sense + * when the index is large, but for an empty index, it's better to use the + * buffer cache to avoid the smgrimmedsync(). + */ + metabuf = ReadBufferExtended(index, INIT_FORKNUM, P_NEW, RBM_NORMAL, NULL); + Assert(BufferGetBlockNumber(metabuf) == BTREE_METAPAGE); + _bt_lockbuf(index, metabuf, BT_WRITE); + + START_CRIT_SECTION(); + + metapage = BufferGetPage(metabuf); _bt_initmetapage(metapage, P_NONE, 0, _bt_allequalimage(index, false)); + MarkBufferDirty(metabuf); + log_newpage_buffer(metabuf, true); - /* - * Write the page and log it. It might seem that an immediate sync would - * be sufficient to guarantee that the file exists on disk, but recovery - * itself might remove it while replaying, for example, an - * XLOG_DBASE_CREATE* or XLOG_TBLSPC_CREATE record. Therefore, we need - * this even when wal_level=minimal. - */ - PageSetChecksumInplace(metapage, BTREE_METAPAGE); - smgrwrite(RelationGetSmgr(index), INIT_FORKNUM, BTREE_METAPAGE, - metapage, true); - log_newpage(&RelationGetSmgr(index)->smgr_rlocator.locator, INIT_FORKNUM, - BTREE_METAPAGE, metapage, true); + END_CRIT_SECTION(); - /* - * An immediate sync is required even if we xlog'd the page, because the - * write did not go through shared_buffers and therefore a concurrent - * checkpoint may have moved the redo pointer past our xlog record. - */ - smgrimmedsync(RelationGetSmgr(index), INIT_FORKNUM); + _bt_unlockbuf(index, metabuf); + ReleaseBuffer(metabuf); } /* diff --git a/src/backend/access/spgist/spginsert.c b/src/backend/access/spgist/spginsert.c index 72d2e1551c..4443f1918d 100644 --- a/src/backend/access/spgist/spginsert.c +++ b/src/backend/access/spgist/spginsert.c @@ -155,49 +155,42 @@ spgbuild(Relation heap, Relation index, IndexInfo *indexInfo) void spgbuildempty(Relation index) { - Page page; - - /* Construct metapage. */ - page = (Page) palloc_aligned(BLCKSZ, PG_IO_ALIGN_SIZE, 0); - SpGistInitMetapage(page); + Buffer metabuffer, + rootbuffer, + nullbuffer; /* - * Write the page and log it unconditionally. This is important - * particularly for indexes created on tablespaces and databases whose - * creation happened after the last redo pointer as recovery removes any - * of their existing content when the corresponding create records are - * replayed. + * Initialize the meta page and root pages */ - PageSetChecksumInplace(page, SPGIST_METAPAGE_BLKNO); - smgrwrite(RelationGetSmgr(index), INIT_FORKNUM, SPGIST_METAPAGE_BLKNO, - page, true); - log_newpage(&(RelationGetSmgr(index))->smgr_rlocator.locator, INIT_FORKNUM, - SPGIST_METAPAGE_BLKNO, page, true); + metabuffer = ReadBufferExtended(index, INIT_FORKNUM, P_NEW, RBM_NORMAL, NULL); + LockBuffer(metabuffer, BUFFER_LOCK_EXCLUSIVE); + rootbuffer = ReadBufferExtended(index, INIT_FORKNUM, P_NEW, RBM_NORMAL, NULL); + LockBuffer(rootbuffer, BUFFER_LOCK_EXCLUSIVE); + nullbuffer = ReadBufferExtended(index, INIT_FORKNUM, P_NEW, RBM_NORMAL, NULL); + LockBuffer(nullbuffer, BUFFER_LOCK_EXCLUSIVE); - /* Likewise for the root page. */ - SpGistInitPage(page, SPGIST_LEAF); + Assert(BufferGetBlockNumber(metabuffer) == SPGIST_METAPAGE_BLKNO); + Assert(BufferGetBlockNumber(rootbuffer) == SPGIST_ROOT_BLKNO); + Assert(BufferGetBlockNumber(nullbuffer) == SPGIST_NULL_BLKNO); - PageSetChecksumInplace(page, SPGIST_ROOT_BLKNO); - smgrwrite(RelationGetSmgr(index), INIT_FORKNUM, SPGIST_ROOT_BLKNO, - page, true); - log_newpage(&(RelationGetSmgr(index))->smgr_rlocator.locator, INIT_FORKNUM, - SPGIST_ROOT_BLKNO, page, true); + START_CRIT_SECTION(); - /* Likewise for the null-tuples root page. */ - SpGistInitPage(page, SPGIST_LEAF | SPGIST_NULLS); + SpGistInitMetapage(BufferGetPage(metabuffer)); + MarkBufferDirty(metabuffer); + SpGistInitBuffer(rootbuffer, SPGIST_LEAF); + MarkBufferDirty(rootbuffer); + SpGistInitBuffer(nullbuffer, SPGIST_LEAF | SPGIST_NULLS); + MarkBufferDirty(nullbuffer); - PageSetChecksumInplace(page, SPGIST_NULL_BLKNO); - smgrwrite(RelationGetSmgr(index), INIT_FORKNUM, SPGIST_NULL_BLKNO, - page, true); - log_newpage(&(RelationGetSmgr(index))->smgr_rlocator.locator, INIT_FORKNUM, - SPGIST_NULL_BLKNO, page, true); + log_newpage_buffer(metabuffer, true); + log_newpage_buffer(rootbuffer, true); + log_newpage_buffer(nullbuffer, true); - /* - * An immediate sync is required even if we xlog'd the pages, because the - * writes did not go through shared buffers and therefore a concurrent - * checkpoint may have moved the redo pointer past our xlog record. - */ - smgrimmedsync(RelationGetSmgr(index), INIT_FORKNUM); + END_CRIT_SECTION(); + + UnlockReleaseBuffer(metabuffer); + UnlockReleaseBuffer(rootbuffer); + UnlockReleaseBuffer(nullbuffer); } /*