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Commit88dd4b0

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committed
Reduce the acceptable staleness of pgstat data for autovacuum, per the
longstanding note in the source that this patch removes.
1 parentb8fab24 commit88dd4b0

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2 files changed

+16
-7
lines changed

2 files changed

+16
-7
lines changed

‎src/backend/postmaster/autovacuum.c

Lines changed: 5 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -55,7 +55,7 @@
5555
*
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*
5757
* IDENTIFICATION
58-
* $PostgreSQL: pgsql/src/backend/postmaster/autovacuum.c,v 1.85 2008/11/02 21:24:52 tgl Exp $
58+
* $PostgreSQL: pgsql/src/backend/postmaster/autovacuum.c,v 1.86 2008/11/03 19:03:41 alvherre Exp $
5959
*
6060
*-------------------------------------------------------------------------
6161
*/
@@ -2149,8 +2149,10 @@ do_autovacuum(void)
21492149
* It could have changed if something else processed the table while
21502150
* we weren't looking.
21512151
*
2152-
* FIXME we ignore the possibility that the table was finished being
2153-
* vacuumed in the last 500ms (PGSTAT_STAT_INTERVAL). This is a bug.
2152+
* Note: we have a special case in pgstat code to ensure that the stats
2153+
* we read are as up-to-date as possible, to avoid the problem that
2154+
* somebody just finished vacuuming this table. The window to the race
2155+
* condition is not closed but it is very small.
21542156
*/
21552157
MemoryContextSwitchTo(AutovacMemCxt);
21562158
tab=table_recheck_autovac(relid,table_toast_map);

‎src/backend/postmaster/pgstat.c

Lines changed: 11 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -13,7 +13,7 @@
1313
*
1414
*Copyright (c) 2001-2008, PostgreSQL Global Development Group
1515
*
16-
*$PostgreSQL: pgsql/src/backend/postmaster/pgstat.c,v 1.182 2008/11/0301:17:08 tgl Exp $
16+
*$PostgreSQL: pgsql/src/backend/postmaster/pgstat.c,v 1.183 2008/11/0319:03:41 alvherre Exp $
1717
* ----------
1818
*/
1919
#include"postgres.h"
@@ -3381,16 +3381,23 @@ backend_read_statsfile(void)
33813381
/*
33823382
* We set the minimum acceptable timestamp to PGSTAT_STAT_INTERVAL msec
33833383
* before now. This indirectly ensures that the collector needn't write
3384-
* the file more often than PGSTAT_STAT_INTERVAL.
3384+
* the file more often than PGSTAT_STAT_INTERVAL. In an autovacuum
3385+
* worker, however, we want a lower delay to avoid using stale data, so we
3386+
* use PGSTAT_RETRY_DELAY (since the number of worker is low, this
3387+
* shouldn't be a problem).
33853388
*
33863389
* Note that we don't recompute min_ts after sleeping; so we might end up
33873390
* accepting a file a bit older than PGSTAT_STAT_INTERVAL. In practice
33883391
* that shouldn't happen, though, as long as the sleep time is less than
33893392
* PGSTAT_STAT_INTERVAL; and we don't want to lie to the collector about
33903393
* what our cutoff time really is.
33913394
*/
3392-
min_ts=TimestampTzPlusMilliseconds(GetCurrentTimestamp(),
3393-
-PGSTAT_STAT_INTERVAL);
3395+
if (IsAutoVacuumWorkerProcess())
3396+
min_ts=TimestampTzPlusMilliseconds(GetCurrentTimestamp(),
3397+
-PGSTAT_RETRY_DELAY);
3398+
else
3399+
min_ts=TimestampTzPlusMilliseconds(GetCurrentTimestamp(),
3400+
-PGSTAT_STAT_INTERVAL);
33943401

33953402
/*
33963403
* Loop until fresh enough stats file is available or we ran out of time.

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