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Remove the "snapshot too old" feature.

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Remove the old_snapshot_threshold setting and mechanism for producing
the error "snapshot too old", originally added by commit 848ef42b.
Unfortunately it had a number of known problems in terms of correctness
and performance, mostly reported by Andres in the course of his work on
snapshot scalability.  We agreed to remove it, after a long period
without an active plan to fix it.

This is certainly a desirable feature, and someone might propose a new
or improved implementation in the future.

Reported-by: Andres Freund <andres@anarazel.de>
Discussion: https://postgr.es/m/CACG%3DezYV%2BEvO135fLRdVn-ZusfVsTY6cH1OZqWtezuEYH6ciQA%40mail.gmail.com
Discussion: https://postgr.es/m/20200401064008.qob7bfnnbu4w5cw4%40alap3.anarazel.de
Discussion: https://postgr.es/m/CA%2BTgmoY%3Daqf0zjTD%2B3dUWYkgMiNDegDLFjo%2B6ze%3DWtpik%2B3XqA%40mail.gmail.com
This commit is contained in:
Thomas Munro
2023-09-05 18:26:12 +12:00
parent aa0d350456
commit f691f5b80a
50 changed files with 21 additions and 1425 deletions
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2
src/backend/access/gin/ginbtree.c
View File

@@ -100,7 +100,6 @@ ginFindLeafPage(GinBtree btree, bool searchMode,
stack->off = InvalidOffsetNumber;
page = BufferGetPage(stack->buffer);
TestForOldSnapshot(snapshot, btree->index, page);
access = ginTraverseLock(stack->buffer, searchMode);
@@ -127,7 +126,6 @@ ginFindLeafPage(GinBtree btree, bool searchMode,
stack->buffer = ginStepRight(stack->buffer, btree->index, access);
stack->blkno = rightlink;
page = BufferGetPage(stack->buffer);
TestForOldSnapshot(snapshot, btree->index, page);
if (!searchMode && GinPageIsIncompleteSplit(page))
ginFinishSplit(btree, stack, false, NULL);

4
src/backend/access/gin/ginget.c
View File

@@ -158,7 +158,6 @@ collectMatchBitmap(GinBtreeData *btree, GinBtreeStack *stack,
return true;
page = BufferGetPage(stack->buffer);
TestForOldSnapshot(snapshot, btree->index, page);
itup = (IndexTuple) PageGetItem(page, PageGetItemId(page, stack->off));
/*
@@ -1460,7 +1459,6 @@ scanGetCandidate(IndexScanDesc scan, pendingPosition *pos)
for (;;)
{
page = BufferGetPage(pos->pendingBuffer);
TestForOldSnapshot(scan->xs_snapshot, scan->indexRelation, page);
maxoff = PageGetMaxOffsetNumber(page);
if (pos->firstOffset > maxoff)
@@ -1641,7 +1639,6 @@ collectMatchesForHeapRow(IndexScanDesc scan, pendingPosition *pos)
sizeof(bool) * (pos->lastOffset - pos->firstOffset));
page = BufferGetPage(pos->pendingBuffer);
TestForOldSnapshot(scan->xs_snapshot, scan->indexRelation, page);
for (i = 0; i < so->nkeys; i++)
{
@@ -1844,7 +1841,6 @@ scanPendingInsert(IndexScanDesc scan, TIDBitmap *tbm, int64 *ntids)
LockBuffer(metabuffer, GIN_SHARE);
page = BufferGetPage(metabuffer);
TestForOldSnapshot(scan->xs_snapshot, scan->indexRelation, page);
blkno = GinPageGetMeta(page)->head;
/*