From ecad16b0bc692180d098bcf39fecfd3d0163c7d9 Mon Sep 17 00:00:00 2001 From: Peter Geoghegan Date: Thu, 7 Nov 2024 16:21:03 -0500 Subject: [PATCH v2] Fix confusion with nbtree parallel scan currPos state. Author: Peter Geoghegan Reported-By: Masahiro Ikeda Diagnosed-By: Masahiro Ikeda Discussion: https://postgr.es/m/f8efb9c0f8d1a71b44fd7f8e42e49c25@oss.nttdata.com --- src/backend/access/nbtree/nbtree.c | 31 ++++++--- src/backend/access/nbtree/nbtsearch.c | 97 +++++++++++---------------- 2 files changed, 62 insertions(+), 66 deletions(-) diff --git a/src/backend/access/nbtree/nbtree.c b/src/backend/access/nbtree/nbtree.c index 2919b1263..cd3c6f4f7 100644 --- a/src/backend/access/nbtree/nbtree.c +++ b/src/backend/access/nbtree/nbtree.c @@ -596,9 +596,7 @@ btparallelrescan(IndexScanDesc scan) * scan, and *last_curr_page returns the page that *next_scan_page came from. * An invalid *next_scan_page means the scan hasn't yet started, or that * caller needs to start the next primitive index scan (if it's the latter - * case we'll set so.needPrimScan). The first time a participating process - * reaches the last page, it will return true and set *next_scan_page to - * P_NONE; after that, further attempts to seize the scan will return false. + * case we'll set so.needPrimScan). * * Callers should ignore the value of *next_scan_page and *last_curr_page if * the return value is false. @@ -724,6 +722,9 @@ _bt_parallel_seize(IndexScanDesc scan, BlockNumber *next_scan_page, * that it can be passed to _bt_parallel_primscan_schedule, should caller * determine that another primitive index scan is required. * + * If caller's next_scan_page is P_NONE, the scan has reached the index's + * rightmost/leftmost page. We'll end the parallel scan right away. + * * Note: unlike the serial case, parallel scans don't need to remember both * sibling links. next_scan_page is whichever link is next given the scan's * direction. That's all we'll ever need, since the direction of a parallel @@ -735,16 +736,30 @@ _bt_parallel_release(IndexScanDesc scan, BlockNumber next_scan_page, { ParallelIndexScanDesc parallel_scan = scan->parallel_scan; BTParallelScanDesc btscan; + bool ended_scan = false; + + Assert(BlockNumberIsValid(next_scan_page)); btscan = (BTParallelScanDesc) OffsetToPointer((void *) parallel_scan, parallel_scan->ps_offset); SpinLockAcquire(&btscan->btps_mutex); - btscan->btps_nextScanPage = next_scan_page; - btscan->btps_lastCurrPage = curr_page; - btscan->btps_pageStatus = BTPARALLEL_IDLE; + if (next_scan_page == P_NONE) + { + btscan->btps_pageStatus = BTPARALLEL_DONE; + ended_scan = true; + } + else + { + btscan->btps_nextScanPage = next_scan_page; + btscan->btps_lastCurrPage = curr_page; + btscan->btps_pageStatus = BTPARALLEL_IDLE; + } SpinLockRelease(&btscan->btps_mutex); - ConditionVariableSignal(&btscan->btps_cv); + if (ended_scan) + ConditionVariableBroadcast(&btscan->btps_cv); + else + ConditionVariableSignal(&btscan->btps_cv); } /* @@ -770,7 +785,7 @@ _bt_parallel_done(IndexScanDesc scan) /* * Should not mark parallel scan done when there's still a pending - * primitive index scan (defensive) + * primitive index scan */ if (so->needPrimScan) return; diff --git a/src/backend/access/nbtree/nbtsearch.c b/src/backend/access/nbtree/nbtsearch.c index 1608dd49d..a3f215e17 100644 --- a/src/backend/access/nbtree/nbtsearch.c +++ b/src/backend/access/nbtree/nbtsearch.c @@ -46,7 +46,8 @@ static bool _bt_steppage(IndexScanDesc scan, ScanDirection dir); static bool _bt_readfirstpage(IndexScanDesc scan, OffsetNumber offnum, ScanDirection dir); static bool _bt_readnextpage(IndexScanDesc scan, BlockNumber blkno, - BlockNumber lastcurrblkno, ScanDirection dir); + BlockNumber lastcurrblkno, ScanDirection dir, + bool seized); static Buffer _bt_lock_and_validate_left(Relation rel, BlockNumber *blkno, BlockNumber lastcurrblkno); static bool _bt_endpoint(IndexScanDesc scan, ScanDirection dir); @@ -924,9 +925,9 @@ _bt_first(IndexScanDesc scan, ScanDirection dir) { BlockNumber blkno, lastcurrblkno; - bool status; - status = _bt_parallel_seize(scan, &blkno, &lastcurrblkno, true); + if (!_bt_parallel_seize(scan, &blkno, &lastcurrblkno, true)) + return false; /* * Initialize arrays (when _bt_parallel_seize didn't already set up @@ -935,14 +936,7 @@ _bt_first(IndexScanDesc scan, ScanDirection dir) if (so->numArrayKeys && !so->needPrimScan) _bt_start_array_keys(scan, dir); - if (!status) - return false; - else if (blkno == P_NONE) - { - _bt_parallel_done(scan); - return false; - } - else if (blkno != InvalidBlockNumber) + if (blkno != InvalidBlockNumber) { Assert(!so->needPrimScan); @@ -950,7 +944,7 @@ _bt_first(IndexScanDesc scan, ScanDirection dir) * We anticipated starting another primitive scan, but some other * worker bet us to it */ - if (!_bt_readnextpage(scan, blkno, lastcurrblkno, dir)) + if (!_bt_readnextpage(scan, blkno, lastcurrblkno, dir, true)) return false; goto readcomplete; } @@ -2012,12 +2006,8 @@ _bt_savepostingitem(BTScanOpaque so, int itemIndex, OffsetNumber offnum, * a valid block, in any case. * * This is a wrapper on _bt_readnextpage that performs final steps for the - * current page. It sets up the _bt_readnextpage call using either local - * state saved in so->currPos by the most recent _bt_readpage call, or using - * shared parallel scan state (obtained by seizing the parallel scan here). - * - * Parallel scan callers that have already seized the scan should directly - * call _bt_readnextpage, rather than calling here. + * current page. It sets up the _bt_readnextpage call using local state saved + * in so->currPos by the most recent _bt_readpage call. */ static bool _bt_steppage(IndexScanDesc scan, ScanDirection dir) @@ -2081,37 +2071,22 @@ _bt_steppage(IndexScanDesc scan, ScanDirection dir) BTScanPosUnpinIfPinned(so->currPos); /* Walk to the next page with data */ - if (!scan->parallel_scan) - { - /* Not parallel, so use local state set by the last _bt_readpage */ - if (ScanDirectionIsForward(dir)) - blkno = so->currPos.nextPage; - else - blkno = so->currPos.prevPage; - lastcurrblkno = so->currPos.currPage; - - /* - * Cancel primitive index scans that were scheduled when the call to - * _bt_readpage for currPos happened to use the opposite direction to - * the one that we're stepping in now. (It's okay to leave the scan's - * array keys as-is, since the next _bt_readpage will advance them.) - */ - if (so->currPos.dir != dir) - so->needPrimScan = false; - } + if (ScanDirectionIsForward(dir)) + blkno = so->currPos.nextPage; else - { - /* - * Seize the scan to get the nextPage and currPage from shared - * parallel state (saved from parallel scan's last _bt_readpage) - */ - if (!_bt_parallel_seize(scan, &blkno, &lastcurrblkno, false)) - return false; + blkno = so->currPos.prevPage; + lastcurrblkno = so->currPos.currPage; - Assert(!so->needPrimScan); - } + /* + * Cancel primitive index scans that were scheduled when the call to + * _bt_readpage for currPos happened to use the opposite direction to the + * one that we're stepping in now. (It's okay to leave the scan's array + * keys as-is, since the next _bt_readpage will advance them.) + */ + if (so->currPos.dir != dir) + so->needPrimScan = false; - return _bt_readnextpage(scan, blkno, lastcurrblkno, dir); + return _bt_readnextpage(scan, blkno, lastcurrblkno, dir, false); } /* @@ -2203,8 +2178,13 @@ _bt_readfirstpage(IndexScanDesc scan, OffsetNumber offnum, ScanDirection dir) * * On entry, caller shouldn't hold any locks or pins on any page (we work * directly off of blkno and lastcurrblkno instead). Parallel scan callers - * must have seized the scan before calling here (blkno and lastcurrblkno - * arguments should come from the seized scan). + * that seized the scan before calling here should pass seized=true; such a + * caller's blkno and lastcurrblkno arguments come from the seized scan. + * seized=false parallel scan callers just pass us the blkno/lastcurrblkno + * taken from their so->currPos, which can be used to end the scan, but will + * never be used to determine which page to read next (we must seize the scan + * to get the blkno that we have to read next, since the correct page to read + * might already be beyond a seized=false caller's blkno). * * On success exit, so->currPos is updated to contain data from the next * interesting page, and we return true (parallel scan callers should not use @@ -2220,12 +2200,12 @@ _bt_readfirstpage(IndexScanDesc scan, OffsetNumber offnum, ScanDirection dir) */ static bool _bt_readnextpage(IndexScanDesc scan, BlockNumber blkno, - BlockNumber lastcurrblkno, ScanDirection dir) + BlockNumber lastcurrblkno, ScanDirection dir, bool seized) { Relation rel = scan->indexRelation; BTScanOpaque so = (BTScanOpaque) scan->opaque; - Assert(so->currPos.currPage == lastcurrblkno || scan->parallel_scan != NULL); + Assert(so->currPos.currPage == lastcurrblkno || seized); Assert(!BTScanPosIsPinned(so->currPos)); /* @@ -2254,6 +2234,14 @@ _bt_readnextpage(IndexScanDesc scan, BlockNumber blkno, Assert(!so->needPrimScan); + /* parallel scan must never actually visit so->currPos blkno */ + if (!seized && scan->parallel_scan != NULL && + !_bt_parallel_seize(scan, &blkno, &lastcurrblkno, false)) + { + BTScanPosInvalidate(so->currPos); + return false; + } + if (ScanDirectionIsForward(dir)) { /* read blkno, but check for interrupts first */ @@ -2308,14 +2296,7 @@ _bt_readnextpage(IndexScanDesc scan, BlockNumber blkno, /* no matching tuples on this page */ _bt_relbuf(rel, so->currPos.buf); - - /* parallel scan seizes another page (won't use so->currPos blkno) */ - if (scan->parallel_scan != NULL && - !_bt_parallel_seize(scan, &blkno, &lastcurrblkno, false)) - { - BTScanPosInvalidate(so->currPos); - return false; - } + seized = false; /* released by _bt_readpage (or by us) */ } /* -- 2.45.2