From a97bbe1f1df9eba0b18207c321c67de80b33db16 Mon Sep 17 00:00:00 2001 From: Andres Freund Date: Sat, 6 Apr 2024 20:51:07 -0700 Subject: [PATCH] Reduce branches in heapgetpage()'s per-tuple loop Until now, heapgetpage()'s loop over all tuples performed some conditional checks for each tuple, even though condition did not change across the loop. This commit fixes that by moving the loop into an inline function. By calling it with different constant arguments, the compiler can generate an optimized loop for the different conditions, at the price of two per-page checks. For cases of all-visible tables and an isolation level other than serializable, speedups of up to 25% have been measured. Reviewed-by: John Naylor Reviewed-by: Zhang Mingli Tested-by: Quan Zongliang Discussion: https://postgr.es/m/20230716015656.xjvemfbp5fysjiea@awork3.anarazel.de Discussion: https://postgr.es/m/2ef7ff1b-3d18-2283-61b1-bbd25fc6c7ce@yeah.net --- src/backend/access/heap/heapam.c | 102 ++++++++++++++++++++++--------- 1 file changed, 74 insertions(+), 28 deletions(-) diff --git a/src/backend/access/heap/heapam.c b/src/backend/access/heap/heapam.c index 01bb2f4cc16..a32acc90473 100644 --- a/src/backend/access/heap/heapam.c +++ b/src/backend/access/heap/heapam.c @@ -364,6 +364,56 @@ heap_setscanlimits(TableScanDesc sscan, BlockNumber startBlk, BlockNumber numBlk scan->rs_numblocks = numBlks; } +/* + * Per-tuple loop for heapgetpage() in pagemode. Pulled out so it can be + * called multiple times, with constant arguments for all_visible, + * check_serializable. + */ +pg_attribute_always_inline +static int +heapgetpage_collect(HeapScanDesc scan, Snapshot snapshot, + Page page, Buffer buffer, + BlockNumber block, int lines, + bool all_visible, bool check_serializable) +{ + int ntup = 0; + OffsetNumber lineoff; + + for (lineoff = FirstOffsetNumber; lineoff <= lines; lineoff++) + { + ItemId lpp = PageGetItemId(page, lineoff); + HeapTupleData loctup; + bool valid; + + if (!ItemIdIsNormal(lpp)) + continue; + + loctup.t_data = (HeapTupleHeader) PageGetItem(page, lpp); + loctup.t_len = ItemIdGetLength(lpp); + loctup.t_tableOid = RelationGetRelid(scan->rs_base.rs_rd); + ItemPointerSet(&(loctup.t_self), block, lineoff); + + if (all_visible) + valid = true; + else + valid = HeapTupleSatisfiesVisibility(&loctup, snapshot, buffer); + + if (check_serializable) + HeapCheckForSerializableConflictOut(valid, scan->rs_base.rs_rd, + &loctup, buffer, snapshot); + + if (valid) + { + scan->rs_vistuples[ntup] = lineoff; + ntup++; + } + } + + Assert(ntup <= MaxHeapTuplesPerPage); + + return ntup; +} + /* * heap_prepare_pagescan - Prepare current scan page to be scanned in pagemode * @@ -379,9 +429,8 @@ heap_prepare_pagescan(TableScanDesc sscan) Snapshot snapshot; Page page; int lines; - int ntup; - OffsetNumber lineoff; bool all_visible; + bool check_serializable; Assert(BufferGetBlockNumber(buffer) == block); @@ -403,7 +452,6 @@ heap_prepare_pagescan(TableScanDesc sscan) page = BufferGetPage(buffer); lines = PageGetMaxOffsetNumber(page); - ntup = 0; /* * If the all-visible flag indicates that all tuples on the page are @@ -426,37 +474,35 @@ heap_prepare_pagescan(TableScanDesc sscan) * tuple for visibility the hard way. */ all_visible = PageIsAllVisible(page) && !snapshot->takenDuringRecovery; + check_serializable = + CheckForSerializableConflictOutNeeded(scan->rs_base.rs_rd, snapshot); - for (lineoff = FirstOffsetNumber; lineoff <= lines; lineoff++) + /* + * We call heapgetpage_collect() with constant arguments, to get the + * compiler to constant fold the constant arguments. Separate calls with + * constant arguments, rather than variables, are needed on several + * compilers to actually perform constant folding. + */ + if (likely(all_visible)) { - ItemId lpp = PageGetItemId(page, lineoff); - HeapTupleData loctup; - bool valid; - - if (!ItemIdIsNormal(lpp)) - continue; - - loctup.t_tableOid = RelationGetRelid(scan->rs_base.rs_rd); - loctup.t_data = (HeapTupleHeader) PageGetItem(page, lpp); - loctup.t_len = ItemIdGetLength(lpp); - ItemPointerSet(&(loctup.t_self), block, lineoff); - - if (all_visible) - valid = true; + if (likely(!check_serializable)) + scan->rs_ntuples = heapgetpage_collect(scan, snapshot, page, buffer, + block, lines, true, false); else - valid = HeapTupleSatisfiesVisibility(&loctup, snapshot, buffer); - - HeapCheckForSerializableConflictOut(valid, scan->rs_base.rs_rd, - &loctup, buffer, snapshot); - - if (valid) - scan->rs_vistuples[ntup++] = lineoff; + scan->rs_ntuples = heapgetpage_collect(scan, snapshot, page, buffer, + block, lines, true, true); + } + else + { + if (likely(!check_serializable)) + scan->rs_ntuples = heapgetpage_collect(scan, snapshot, page, buffer, + block, lines, false, false); + else + scan->rs_ntuples = heapgetpage_collect(scan, snapshot, page, buffer, + block, lines, false, true); } LockBuffer(buffer, BUFFER_LOCK_UNLOCK); - - Assert(ntup <= MaxHeapTuplesPerPage); - scan->rs_ntuples = ntup; } /*