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Commitc242baa

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Consider triggering VACUUM failsafe during scan.
The wraparound failsafe mechanism added by commit1e55e7d handled theone-pass strategy case (i.e. the "table has no indexes" case) by addinga dedicated failsafe check. This made up for the fact that the usualone-pass checks inside lazy_vacuum_all_indexes() cannot ever be reachedduring a one-pass strategy VACUUM.This approach failed to account for two-pass VACUUMs that opt out ofindex vacuuming up-front. The INDEX_CLEANUP off case in the only casethat works like that.Fix this by performing a failsafe check every 4GB during the first scanof the heap, regardless of the details of the VACUUM. This eliminatesthe special case, and will make the failsafe trigger more reliably.Author: Peter Geoghegan <pg@bowt.ie>Reported-By: Andres Freund <andres@anarazel.de>Reviewed-By: Masahiko Sawada <sawada.mshk@gmail.com>Discussion:https://postgr.es/m/20210424002921.pb3t7h6frupdqnkp@alap3.anarazel.de
1 parent713a431 commitc242baa

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1 file changed

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‎src/backend/access/heap/vacuumlazy.c

Lines changed: 19 additions & 24 deletions
Original file line numberDiff line numberDiff line change
@@ -110,10 +110,9 @@
110110
#defineBYPASS_THRESHOLD_PAGES0.02/* i.e. 2% of rel_pages */
111111

112112
/*
113-
* When a table is small (i.e. smaller than this), save cycles by avoiding
114-
* repeated failsafe checks
113+
* Perform a failsafe check every 4GB during the heap scan, approximately
115114
*/
116-
#defineFAILSAFE_MIN_PAGES \
115+
#defineFAILSAFE_EVERY_PAGES \
117116
((BlockNumber) (((uint64) 4 * 1024 * 1024 * 1024) / BLCKSZ))
118117

119118
/*
@@ -890,6 +889,7 @@ lazy_scan_heap(LVRelState *vacrel, VacuumParams *params, bool aggressive)
890889
BlockNumbernblocks,
891890
blkno,
892891
next_unskippable_block,
892+
next_failsafe_block,
893893
next_fsm_block_to_vacuum;
894894
PGRUsageru0;
895895
Buffervmbuffer=InvalidBuffer;
@@ -919,6 +919,7 @@ lazy_scan_heap(LVRelState *vacrel, VacuumParams *params, bool aggressive)
919919

920920
nblocks=RelationGetNumberOfBlocks(vacrel->rel);
921921
next_unskippable_block=0;
922+
next_failsafe_block=0;
922923
next_fsm_block_to_vacuum=0;
923924
vacrel->rel_pages=nblocks;
924925
vacrel->scanned_pages=0;
@@ -1130,6 +1131,20 @@ lazy_scan_heap(LVRelState *vacrel, VacuumParams *params, bool aggressive)
11301131

11311132
vacuum_delay_point();
11321133

1134+
/*
1135+
* Regularly check if wraparound failsafe should trigger.
1136+
*
1137+
* There is a similar check inside lazy_vacuum_all_indexes(), but
1138+
* relfrozenxid might start to look dangerously old before we reach
1139+
* that point. This check also provides failsafe coverage for the
1140+
* one-pass strategy case.
1141+
*/
1142+
if (blkno-next_failsafe_block >=FAILSAFE_EVERY_PAGES)
1143+
{
1144+
lazy_check_wraparound_failsafe(vacrel);
1145+
next_failsafe_block=blkno;
1146+
}
1147+
11331148
/*
11341149
* Consider if we definitely have enough space to process TIDs on page
11351150
* already. If we are close to overrunning the available space for
@@ -1375,17 +1390,12 @@ lazy_scan_heap(LVRelState *vacrel, VacuumParams *params, bool aggressive)
13751390
* Periodically perform FSM vacuuming to make newly-freed
13761391
* space visible on upper FSM pages. Note we have not yet
13771392
* performed FSM processing for blkno.
1378-
*
1379-
* Call lazy_check_wraparound_failsafe() here, too, since we
1380-
* also don't want to do that too frequently, or too
1381-
* infrequently.
13821393
*/
13831394
if (blkno-next_fsm_block_to_vacuum >=VACUUM_FSM_EVERY_PAGES)
13841395
{
13851396
FreeSpaceMapVacuumRange(vacrel->rel,next_fsm_block_to_vacuum,
13861397
blkno);
13871398
next_fsm_block_to_vacuum=blkno;
1388-
lazy_check_wraparound_failsafe(vacrel);
13891399
}
13901400

13911401
/*
@@ -2558,7 +2568,6 @@ lazy_check_needs_freeze(Buffer buf, bool *hastup, LVRelState *vacrel)
25582568
/*
25592569
* Trigger the failsafe to avoid wraparound failure when vacrel table has a
25602570
* relfrozenxid and/or relminmxid that is dangerously far in the past.
2561-
*
25622571
* Triggering the failsafe makes the ongoing VACUUM bypass any further index
25632572
* vacuuming and heap vacuuming. Truncating the heap is also bypassed.
25642573
*
@@ -2567,24 +2576,10 @@ lazy_check_needs_freeze(Buffer buf, bool *hastup, LVRelState *vacrel)
25672576
* that it started out with.
25682577
*
25692578
* Returns true when failsafe has been triggered.
2570-
*
2571-
* Caller is expected to call here before and after vacuuming each index in
2572-
* the case of two-pass VACUUM, or every VACUUM_FSM_EVERY_PAGES blocks in the
2573-
* case of no-indexes/one-pass VACUUM.
2574-
*
2575-
* There is also a precheck before the first pass over the heap begins, which
2576-
* is helpful when the failsafe initially triggers during a non-aggressive
2577-
* VACUUM -- the automatic aggressive vacuum to prevent wraparound that
2578-
* follows can independently trigger the failsafe right away.
25792579
*/
25802580
staticbool
25812581
lazy_check_wraparound_failsafe(LVRelState*vacrel)
25822582
{
2583-
/* Avoid calling vacuum_xid_failsafe_check() very frequently */
2584-
if (vacrel->num_index_scans==0&&
2585-
vacrel->rel_pages <=FAILSAFE_MIN_PAGES)
2586-
return false;
2587-
25882583
/* Don't warn more than once per VACUUM */
25892584
if (vacrel->do_failsafe)
25902585
return true;
@@ -2600,7 +2595,7 @@ lazy_check_wraparound_failsafe(LVRelState *vacrel)
26002595
vacrel->do_failsafe= true;
26012596

26022597
ereport(WARNING,
2603-
(errmsg("abandoned index vacuuming of table \"%s.%s.%s\" as a failsafe after %d index scans",
2598+
(errmsg("bypassing nonessential maintenance of table \"%s.%s.%s\" as a failsafe after %d index scans",
26042599
get_database_name(MyDatabaseId),
26052600
vacrel->relnamespace,
26062601
vacrel->relname,

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