From 377c195bccf2dd2529e64d0d453104485f7662b7 Mon Sep 17 00:00:00 2001 From: Melanie Plageman Date: Fri, 4 Mar 2022 15:52:45 -0500 Subject: [PATCH v6 4/4] Use shared buffers when possible for index build When there are not too many tuples, building the index in shared buffers makes sense. It allows the buffer manager to handle how best to do the IO. --- src/backend/access/nbtree/nbtree.c | 32 ++-- src/backend/access/nbtree/nbtsort.c | 273 +++++++++++++++++++++------- 2 files changed, 223 insertions(+), 82 deletions(-) diff --git a/src/backend/access/nbtree/nbtree.c b/src/backend/access/nbtree/nbtree.c index fc5cce4603..d3982b9388 100644 --- a/src/backend/access/nbtree/nbtree.c +++ b/src/backend/access/nbtree/nbtree.c @@ -152,34 +152,24 @@ void btbuildempty(Relation index) { Page metapage; - UnBufferedWriteState wstate; + Buffer metabuf; /* - * Though this is an unlogged relation, pass do_wal=true since the init - * fork of an unlogged index must be wal-logged and fsync'd. This currently - * has no effect, as unbuffered_write() does not do log_newpage() - * internally. However, were this to be replaced with unbuffered_extend(), - * do_wal must be true to ensure the data is logged and fsync'd. + * Allocate a buffer for metapage and initialize metapage. */ - unbuffered_prep(&wstate, true, true); - - /* Construct metapage. */ - metapage = (Page) palloc(BLCKSZ); + metabuf = ReadBufferExtended(index, INIT_FORKNUM, P_NEW, RBM_ZERO_AND_LOCK, + NULL); + metapage = BufferGetPage(metabuf); _bt_initmetapage(metapage, P_NONE, 0, _bt_allequalimage(index, false)); /* - * 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. + * Mark metapage buffer as dirty and XLOG it */ - unbuffered_write(&wstate, RelationGetSmgr(index), INIT_FORKNUM, - BTREE_METAPAGE, metapage); - log_newpage(&RelationGetSmgr(index)->smgr_rnode.node, INIT_FORKNUM, - BTREE_METAPAGE, metapage, true); - - unbuffered_finish(&wstate, RelationGetSmgr(index), INIT_FORKNUM); + START_CRIT_SECTION(); + MarkBufferDirty(metabuf); + log_newpage_buffer(metabuf, true); + END_CRIT_SECTION(); + _bt_relbuf(index, metabuf); } /* diff --git a/src/backend/access/nbtree/nbtsort.c b/src/backend/access/nbtree/nbtsort.c index f1b9e2e24e..35ded6e4a1 100644 --- a/src/backend/access/nbtree/nbtsort.c +++ b/src/backend/access/nbtree/nbtsort.c @@ -23,13 +23,15 @@ * many upper pages if the keys are reasonable-size) without risking a lot of * cascading splits during early insertions. * - * Formerly the index pages being built were kept in shared buffers, but that - * is of no value (since other backends have no interest in them yet) and it - * created locking problems for CHECKPOINT, because the upper-level pages were - * held exclusive-locked for long periods. Now we just build the pages in - * local memory and write or extend them with directmgr as we finish them. - * They will need to be re-read into shared buffers on first use after the - * build finishes. + * If indexing little enough data, it can be built efficiently in shared + * buffers, leaving checkpointer to deal with fsync'ing the data at its + * convenience. However, if indexing many pages, building the index in shared + * buffers could delay CHECKPOINTs--since the upper-level pages are + * exclusive-locked for long periods. In that case, build the pages in local + * memory and write or extend them with directmgr as they are finished. If a + * CHECKPOINT has begun since the build started, directmgr will fsync the + * relation file itself after finishing the build. The index will then need to + * be re-read into shared buffers on first use after the build finishes. * * This code isn't concerned about the FSM at all. The caller is responsible * for initializing that. @@ -236,6 +238,7 @@ typedef struct BTPageState { Page btps_page; /* workspace for page building */ BlockNumber btps_blkno; /* block # to write this page at */ + Buffer btps_buf; /* buffer to write this page to */ IndexTuple btps_lowkey; /* page's strict lower bound pivot tuple */ OffsetNumber btps_lastoff; /* last item offset loaded */ Size btps_lastextra; /* last item's extra posting list space */ @@ -253,10 +256,26 @@ typedef struct BTWriteState Relation index; BTScanInsert inskey; /* generic insertion scankey */ bool btws_use_wal; /* dump pages to WAL? */ - BlockNumber btws_pages_alloced; /* # pages allocated */ - BlockNumber btws_pages_written; /* # pages written out */ + BlockNumber btws_pages_alloced; /* # pages allocated for index builds outside SB */ + BlockNumber btws_pages_written; /* # pages written out for index builds outside SB */ Page btws_zeropage; /* workspace for filling zeroes */ UnBufferedWriteState ub_wstate; + /* + * Allocate a new btree page. This does not initialize the page. + */ + Page (*_bt_bl_alloc_page) (struct BTWriteState *wstate, BlockNumber + *blockno, Buffer *buf); + /* + * Emit a completed btree page, and release the working storage. + */ + void (*_bt_blwritepage) (struct BTWriteState *wstate, Page page, + BlockNumber blkno, Buffer buf); + + void (*_bt_bl_unbuffered_prep) (UnBufferedWriteState *wstate, bool do_wal, + bool do_optimization); + + void (*_bt_bl_unbuffered_finish) (UnBufferedWriteState *wstate, + SMgrRelation smgrrel, ForkNumber forknum); } BTWriteState; @@ -265,10 +284,22 @@ static double _bt_spools_heapscan(Relation heap, Relation index, static void _bt_spooldestroy(BTSpool *btspool); static void _bt_spool(BTSpool *btspool, ItemPointer self, Datum *values, bool *isnull); -static void _bt_leafbuild(BTSpool *btspool, BTSpool *btspool2); +static void _bt_leafbuild(BTWriteState *wstate, BTSpool *btspool, BTSpool *btspool2); static void _bt_build_callback(Relation index, ItemPointer tid, Datum *values, bool *isnull, bool tupleIsAlive, void *state); -static Page _bt_blnewpage(uint32 level); + +static Page +_bt_bl_alloc_page_direct(BTWriteState *wstate, BlockNumber *blockno, Buffer *buf); +static Page +_bt_bl_alloc_page_shared(BTWriteState *wstate, BlockNumber *blockno, Buffer *buf); + +static Page _bt_blnewpage(uint32 level, Page page); + +static void +_bt_blwritepage_direct(BTWriteState *wstate, Page page, BlockNumber blkno, Buffer buf); +static void +_bt_blwritepage_shared(BTWriteState *wstate, Page page, BlockNumber blkno, Buffer buf); + static BTPageState *_bt_pagestate(BTWriteState *wstate, uint32 level); static void _bt_slideleft(Page rightmostpage); static void _bt_sortaddtup(Page page, Size itemsize, @@ -279,9 +310,10 @@ static void _bt_buildadd(BTWriteState *wstate, BTPageState *state, static void _bt_sort_dedup_finish_pending(BTWriteState *wstate, BTPageState *state, BTDedupState dstate); -static void _bt_uppershutdown(BTWriteState *wstate, BTPageState *state); static void _bt_load(BTWriteState *wstate, BTSpool *btspool, BTSpool *btspool2); +static void _bt_uppershutdown(BTWriteState *wstate, BTPageState *state, Buffer + metabuf, Page metapage); static void _bt_begin_parallel(BTBuildState *buildstate, bool isconcurrent, int request); static void _bt_end_parallel(BTLeader *btleader); @@ -294,6 +326,21 @@ static void _bt_parallel_scan_and_sort(BTSpool *btspool, BTSpool *btspool2, Sharedsort *sharedsort2, int sortmem, bool progress); +#define BT_BUILD_SB_THRESHOLD 1024 + +static const BTWriteState wstate_shared = { + ._bt_bl_alloc_page = _bt_bl_alloc_page_shared, + ._bt_blwritepage = _bt_blwritepage_shared, + ._bt_bl_unbuffered_prep = NULL, + ._bt_bl_unbuffered_finish = NULL, +}; + +static const BTWriteState wstate_direct = { + ._bt_bl_alloc_page = _bt_bl_alloc_page_direct, + ._bt_blwritepage = _bt_blwritepage_direct, + ._bt_bl_unbuffered_prep = unbuffered_prep, + ._bt_bl_unbuffered_finish = unbuffered_finish, +}; /* * btbuild() -- build a new btree index. @@ -303,6 +350,7 @@ btbuild(Relation heap, Relation index, IndexInfo *indexInfo) { IndexBuildResult *result; BTBuildState buildstate; + BTWriteState writestate; double reltuples; #ifdef BTREE_BUILD_STATS @@ -333,8 +381,12 @@ btbuild(Relation heap, Relation index, IndexInfo *indexInfo) * Finish the build by (1) completing the sort of the spool file, (2) * inserting the sorted tuples into btree pages and (3) building the upper * levels. Finally, it may also be necessary to end use of parallelism. + * + * Don't use shared buffers if the number of tuples is too large. */ - _bt_leafbuild(buildstate.spool, buildstate.spool2); + writestate = reltuples < BT_BUILD_SB_THRESHOLD ? wstate_shared : wstate_direct; + + _bt_leafbuild(&writestate, buildstate.spool, buildstate.spool2); _bt_spooldestroy(buildstate.spool); if (buildstate.spool2) _bt_spooldestroy(buildstate.spool2); @@ -542,10 +594,8 @@ _bt_spool(BTSpool *btspool, ItemPointer self, Datum *values, bool *isnull) * create an entire btree. */ static void -_bt_leafbuild(BTSpool *btspool, BTSpool *btspool2) +_bt_leafbuild(BTWriteState *wstate, BTSpool *btspool, BTSpool *btspool2) { - BTWriteState wstate; - #ifdef BTREE_BUILD_STATS if (log_btree_build_stats) { @@ -565,21 +615,38 @@ _bt_leafbuild(BTSpool *btspool, BTSpool *btspool2) tuplesort_performsort(btspool2->sortstate); } - wstate.heap = btspool->heap; - wstate.index = btspool->index; - wstate.inskey = _bt_mkscankey(wstate.index, NULL); - /* _bt_mkscankey() won't set allequalimage without metapage */ - wstate.inskey->allequalimage = _bt_allequalimage(wstate.index, true); - wstate.btws_use_wal = RelationNeedsWAL(wstate.index); + wstate->heap = btspool->heap; + wstate->index = btspool->index; + wstate->inskey = _bt_mkscankey(wstate->index, NULL); + /* _bt-mkscankey() won't set allequalimage without metapage */ + wstate->inskey->allequalimage = _bt_allequalimage(wstate->index, true); + wstate->btws_use_wal = RelationNeedsWAL(wstate->index); /* reserve the metapage */ - wstate.btws_pages_alloced = BTREE_METAPAGE + 1; - wstate.btws_pages_written = 0; - wstate.btws_zeropage = NULL; /* until needed */ + wstate->btws_pages_alloced = 0; + wstate->btws_pages_written = 0; + wstate->btws_zeropage = NULL; pgstat_progress_update_param(PROGRESS_CREATEIDX_SUBPHASE, PROGRESS_BTREE_PHASE_LEAF_LOAD); - _bt_load(&wstate, btspool, btspool2); + + /* + * If not using shared buffers, for a WAL-logged relation, save the redo + * pointer location in case a checkpoint begins during the index build. + */ + if (wstate->_bt_bl_unbuffered_prep) + wstate->_bt_bl_unbuffered_prep(&wstate->ub_wstate, + wstate->btws_use_wal, wstate->btws_use_wal); + + _bt_load(wstate, btspool, btspool2); + + /* + * If not using shared buffers, for a WAL-logged relation, check if backend + * must fsync the page itself. + */ + if (wstate->_bt_bl_unbuffered_finish) + wstate->_bt_bl_unbuffered_finish(&wstate->ub_wstate, + RelationGetSmgr(wstate->index), MAIN_FORKNUM); } /* @@ -612,15 +679,15 @@ _bt_build_callback(Relation index, } /* - * allocate workspace for a new, clean btree page, not linked to any siblings. + * Set up workspace for a new, clean btree page, not linked to any siblings. + * Caller must allocate the passed in page. */ static Page -_bt_blnewpage(uint32 level) +_bt_blnewpage(uint32 level, Page page) { - Page page; BTPageOpaque opaque; - page = (Page) palloc(BLCKSZ); + Assert(page); /* Zero the page and set up standard page header info */ _bt_pageinit(page, BLCKSZ); @@ -638,11 +705,8 @@ _bt_blnewpage(uint32 level) return page; } -/* - * emit a completed btree page, and release the working storage. - */ static void -_bt_blwritepage(BTWriteState *wstate, Page page, BlockNumber blkno) +_bt_blwritepage_direct(BTWriteState *wstate, Page page, BlockNumber blkno, Buffer buf) { /* * If we have to write pages nonsequentially, fill in the space with @@ -685,6 +749,61 @@ _bt_blwritepage(BTWriteState *wstate, Page page, BlockNumber blkno) pfree(page); } +static void +_bt_blwritepage_shared(BTWriteState *wstate, Page page, BlockNumber blkno, Buffer buf) +{ + /* + * Indexes built in shared buffers need only to mark the buffer as dirty + * and XLOG it. + */ + Assert(buf); + START_CRIT_SECTION(); + MarkBufferDirty(buf); + if (wstate->btws_use_wal) + log_newpage_buffer(buf, true); + END_CRIT_SECTION(); + _bt_relbuf(wstate->index, buf); +} + +static Page +_bt_bl_alloc_page_direct(BTWriteState *wstate, BlockNumber *blockno, Buffer *buf) +{ + /* buf is only used when using shared buffers, so set it to InvalidBuffer */ + *buf = InvalidBuffer; + + /* + * Assign block number for the page. + * This will be used to link to sibling page(s) later and, if this is the + * initial page in the level, saved in the BTPageState + */ + *blockno = wstate->btws_pages_alloced++; + + /* now allocate and set up the new page */ + return palloc(BLCKSZ); +} + +static Page +_bt_bl_alloc_page_shared(BTWriteState *wstate, BlockNumber *blockno, Buffer *buf) +{ + /* + * Find a shared buffer for the page. Pass mode RBM_ZERO_AND_LOCK to get an + * exclusive lock on the buffer content. No lock on the relation as a whole + * is needed (as in LockRelationForExtension()) because the initial index + * build is not yet complete. + */ + *buf = ReadBufferExtended(wstate->index, MAIN_FORKNUM, P_NEW, + RBM_ZERO_AND_LOCK, NULL); + + /* + * bufmgr will assign a block number for the new page. + * This will be used to link to sibling page(s) later and, if this is the + * initial page in the level, saved in the BTPageState + */ + *blockno = BufferGetBlockNumber(*buf); + + return BufferGetPage(*buf); +} + /* * allocate and initialize a new BTPageState. the returned structure * is suitable for immediate use by _bt_buildadd. @@ -692,13 +811,20 @@ _bt_blwritepage(BTWriteState *wstate, Page page, BlockNumber blkno) static BTPageState * _bt_pagestate(BTWriteState *wstate, uint32 level) { + Buffer buf; + BlockNumber blockno; + BTPageState *state = (BTPageState *) palloc0(sizeof(BTPageState)); - /* create initial page for level */ - state->btps_page = _bt_blnewpage(level); + /* + * Allocate and initialize initial page for the level, and if using shared + * buffers, extend the relation and allocate a shared buffer for the block. + */ + state->btps_page = _bt_blnewpage(level, wstate->_bt_bl_alloc_page(wstate, + &blockno, &buf)); - /* and assign it a page position */ - state->btps_blkno = wstate->btws_pages_alloced++; + state->btps_blkno = blockno; + state->btps_buf = buf; state->btps_lowkey = NULL; /* initialize lastoff so first item goes into P_FIRSTKEY */ @@ -833,6 +959,7 @@ _bt_buildadd(BTWriteState *wstate, BTPageState *state, IndexTuple itup, { Page npage; BlockNumber nblkno; + Buffer nbuf; OffsetNumber last_off; Size last_truncextra; Size pgspc; @@ -847,6 +974,7 @@ _bt_buildadd(BTWriteState *wstate, BTPageState *state, IndexTuple itup, npage = state->btps_page; nblkno = state->btps_blkno; + nbuf = state->btps_buf; last_off = state->btps_lastoff; last_truncextra = state->btps_lastextra; state->btps_lastextra = truncextra; @@ -903,15 +1031,14 @@ _bt_buildadd(BTWriteState *wstate, BTPageState *state, IndexTuple itup, */ Page opage = npage; BlockNumber oblkno = nblkno; + Buffer obuf = nbuf; ItemId ii; ItemId hii; IndexTuple oitup; - /* Create new page of same level */ - npage = _bt_blnewpage(state->btps_level); - - /* and assign it a page position */ - nblkno = wstate->btws_pages_alloced++; + /* Create and initialize a new page of same level */ + npage = _bt_blnewpage(state->btps_level, + wstate->_bt_bl_alloc_page(wstate, &nblkno, &nbuf)); /* * We copy the last item on the page into the new page, and then @@ -1021,9 +1148,12 @@ _bt_buildadd(BTWriteState *wstate, BTPageState *state, IndexTuple itup, /* * Write out the old page. We never need to touch it again, so we can - * free the opage workspace too. + * free the opage workspace too. obuf has been released and is no longer + * valid. */ - _bt_blwritepage(wstate, opage, oblkno); + wstate->_bt_blwritepage(wstate, opage, oblkno, obuf); + obuf = InvalidBuffer; + opage = NULL; /* * Reset last_off to point to new page @@ -1058,6 +1188,7 @@ _bt_buildadd(BTWriteState *wstate, BTPageState *state, IndexTuple itup, state->btps_page = npage; state->btps_blkno = nblkno; + state->btps_buf = nbuf; state->btps_lastoff = last_off; } @@ -1103,12 +1234,12 @@ _bt_sort_dedup_finish_pending(BTWriteState *wstate, BTPageState *state, * Finish writing out the completed btree. */ static void -_bt_uppershutdown(BTWriteState *wstate, BTPageState *state) +_bt_uppershutdown(BTWriteState *wstate, BTPageState *state, Buffer metabuf, + Page metapage) { BTPageState *s; BlockNumber rootblkno = P_NONE; uint32 rootlevel = 0; - Page metapage; /* * Each iteration of this loop completes one more level of the tree. @@ -1154,20 +1285,24 @@ _bt_uppershutdown(BTWriteState *wstate, BTPageState *state) * back one slot. Then we can dump out the page. */ _bt_slideleft(s->btps_page); - _bt_blwritepage(wstate, s->btps_page, s->btps_blkno); + wstate->_bt_blwritepage(wstate, s->btps_page, s->btps_blkno, s->btps_buf); + s->btps_buf = InvalidBuffer; s->btps_page = NULL; /* writepage freed the workspace */ } /* - * As the last step in the process, construct the metapage and make it + * As the last step in the process, initialize the metapage and make it * point to the new root (unless we had no data at all, in which case it's * set to point to "P_NONE"). This changes the index to the "valid" state * by filling in a valid magic number in the metapage. + * After this, metapage will have been freed or invalid and metabuf, if ever + * valid, will have been released. */ - metapage = (Page) palloc(BLCKSZ); _bt_initmetapage(metapage, rootblkno, rootlevel, wstate->inskey->allequalimage); - _bt_blwritepage(wstate, metapage, BTREE_METAPAGE); + wstate->_bt_blwritepage(wstate, metapage, BTREE_METAPAGE, metabuf); + metabuf = InvalidBuffer; + metapage = NULL; } /* @@ -1177,6 +1312,10 @@ _bt_uppershutdown(BTWriteState *wstate, BTPageState *state) static void _bt_load(BTWriteState *wstate, BTSpool *btspool, BTSpool *btspool2) { + Page metapage; + BlockNumber metablkno; + Buffer metabuf; + BTPageState *state = NULL; bool merge = (btspool2 != NULL); IndexTuple itup, @@ -1189,15 +1328,30 @@ _bt_load(BTWriteState *wstate, BTSpool *btspool, BTSpool *btspool2) int64 tuples_done = 0; bool deduplicate; - /* - * The fsync optimization done by directmgr is only relevant if - * WAL-logging, so pass btws_use_wal for this parameter. - */ - unbuffered_prep(&wstate->ub_wstate, wstate->btws_use_wal, wstate->btws_use_wal); - deduplicate = wstate->inskey->allequalimage && !btspool->isunique && BTGetDeduplicateItems(wstate->index); + /* + * Reserve block 0 for the metapage up front. + * + * When using the shared buffers API it is easier to allocate the buffer + * for block 0 first instead of trying skip block 0 and allocate it at the + * end of index build. + * + * When not using the shared buffers API, there is no harm in allocating + * the metapage first. When block 1 is written, the direct writepage + * function will zero-fill block 0. When writing out the metapage at the + * end of index build, it will overwrite that block 0. + * + * The metapage will be initialized and written out at the end of the index + * build when all of the information needed to do so is available. + * + * The block number will always be BTREE_METAPAGE, so the metablkno + * variable is unused and only created to avoid a special case in the + * direct alloc function. + */ + metapage = wstate->_bt_bl_alloc_page(wstate, &metablkno, &metabuf); + if (merge) { /* @@ -1419,10 +1573,7 @@ _bt_load(BTWriteState *wstate, BTSpool *btspool, BTSpool *btspool2) } /* Close down final pages and write the metapage */ - _bt_uppershutdown(wstate, state); - - unbuffered_finish(&wstate->ub_wstate, RelationGetSmgr(wstate->index), - MAIN_FORKNUM); + _bt_uppershutdown(wstate, state, metabuf, metapage); } /* -- 2.30.2