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Commit4c08ecd

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Fix assertion when decrementing eager scanning success and failure counters.
Previously, we asserted that the eager scan's success and failurecounters were positive before decrementing them. However, thisassumption was incorrect, as it's possible that some blocks havealready been eagerly scanned by the time eager scanning is disabled.This commit replaces the assertions with guards to handle thisscenario gracefully.With this change, we continue to allow read-ahead operations by theread stream that exceed the success and failure caps. While there is apossibility that overruns will trigger eager scans of additionalpages, this does not pose a practical concern as the overruns will notbe substantial and remain within an acceptable range.Reviewed-by: Melanie Plageman <melanieplageman@gmail.com>Discussion:https://postgr.es/m/CAD21AoConf6tkVCv-=JhQJj56kYsDwo4jG5+WqgT+ukSkYomSQ@mail.gmail.com
1 parentc53f3b9 commit4c08ecd

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1 file changed

+17
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‎src/backend/access/heap/vacuumlazy.c

Lines changed: 17 additions & 12 deletions
Original file line numberDiff line numberDiff line change
@@ -1413,11 +1413,25 @@ lazy_scan_heap(LVRelState *vacrel)
14131413

14141414
if (vm_page_frozen)
14151415
{
1416-
Assert(vacrel->eager_scan_remaining_successes>0);
1417-
vacrel->eager_scan_remaining_successes--;
1416+
if(vacrel->eager_scan_remaining_successes>0)
1417+
vacrel->eager_scan_remaining_successes--;
14181418

14191419
if (vacrel->eager_scan_remaining_successes==0)
14201420
{
1421+
/*
1422+
* Report only once that we disabled eager scanning. We
1423+
* may eagerly read ahead blocks in excess of the success
1424+
* or failure caps before attempting to freeze them, so we
1425+
* could reach here even after disabling additional eager
1426+
* scanning.
1427+
*/
1428+
if (vacrel->eager_scan_max_fails_per_region>0)
1429+
ereport(vacrel->verbose ?INFO :DEBUG2,
1430+
(errmsg("disabling eager scanning after freezing %u eagerly scanned blocks of \"%s.%s.%s\"",
1431+
orig_eager_scan_success_limit,
1432+
vacrel->dbname,vacrel->relnamespace,
1433+
vacrel->relname)));
1434+
14211435
/*
14221436
* If we hit our success cap, permanently disable eager
14231437
* scanning by setting the other eager scan management
@@ -1426,19 +1440,10 @@ lazy_scan_heap(LVRelState *vacrel)
14261440
vacrel->eager_scan_remaining_fails=0;
14271441
vacrel->next_eager_scan_region_start=InvalidBlockNumber;
14281442
vacrel->eager_scan_max_fails_per_region=0;
1429-
1430-
ereport(vacrel->verbose ?INFO :DEBUG2,
1431-
(errmsg("disabling eager scanning after freezing %u eagerly scanned blocks of \"%s.%s.%s\"",
1432-
orig_eager_scan_success_limit,
1433-
vacrel->dbname,vacrel->relnamespace,
1434-
vacrel->relname)));
14351443
}
14361444
}
1437-
else
1438-
{
1439-
Assert(vacrel->eager_scan_remaining_fails>0);
1445+
elseif (vacrel->eager_scan_remaining_fails>0)
14401446
vacrel->eager_scan_remaining_fails--;
1441-
}
14421447
}
14431448

14441449
/*

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