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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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5
src/backend/access/heap/vacuumlazy.c
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@ -1588,7 +1588,7 @@ retry:
* that were deleted from indexes.
*/
tuples_deleted = heap_page_prune(rel, buf, vacrel->vistest,
InvalidTransactionId, 0, &nnewlpdead,
&nnewlpdead,
&vacrel->offnum);
/*
@ -2875,8 +2875,7 @@ should_attempt_truncation(LVRelState *vacrel)
{
BlockNumber possibly_freeable;
if (!vacrel->do_rel_truncate || VacuumFailsafeActive ||
old_snapshot_threshold >= 0)
if (!vacrel->do_rel_truncate || VacuumFailsafeActive)
return false;
possibly_freeable = vacrel->rel_pages - vacrel->nonempty_pages;