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Rethink prior patch to filter out dead backend entries from the pgstats

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file.  The original code probed the PGPROC array separately for each PID,
which was not good for large numbers of backends: not only is the runtime
O(N^2) but most of it is spent holding ProcArrayLock.  Instead, take the
lock just once and copy the active PIDs into an array, then use qsort
and bsearch so that the lookup time is more like O(N log N).
This commit is contained in:
Tom Lane
2005-12-16 04:03:40 +00:00
parent 4ce6be4f5e
commit fb3dbdf986
3 changed files with 64 additions and 7 deletions
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30
src/backend/postmaster/pgstat.c
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@ -13,7 +13,7 @@
*
* Copyright (c) 2001-2005, PostgreSQL Global Development Group
*
* $PostgreSQL: pgsql/src/backend/postmaster/pgstat.c,v 1.112 2005/11/22 18:17:17 momjian Exp $
* $PostgreSQL: pgsql/src/backend/postmaster/pgstat.c,v 1.113 2005/12/16 04:03:40 tgl Exp $
* ----------
*/
#include "postgres.h"
@ -2453,6 +2453,16 @@ pgstat_write_statsfile(void)
}
}
/*
* qsort/bsearch comparison routine for PIDs
*
* We assume PIDs are nonnegative, so there's no overflow risk
*/
static int
comparePids(const void *v1, const void *v2)
{
return *((const int *) v1) - *((const int *) v2);
}
/* ----------
* pgstat_read_statsfile() -
@ -2478,7 +2488,7 @@ pgstat_read_statsfile(HTAB **dbhash, Oid onlydb,
int maxbackends = 0;
int havebackends = 0;
bool found;
bool check_pids;
int *live_pids;
MemoryContext use_mcxt;
int mcxt_flags;
@ -2497,13 +2507,17 @@ pgstat_read_statsfile(HTAB **dbhash, Oid onlydb,
{
use_mcxt = NULL;
mcxt_flags = 0;
check_pids = false;
live_pids = NULL;
}
else
{
use_mcxt = TopTransactionContext;
mcxt_flags = HASH_CONTEXT;
check_pids = true;
live_pids = GetAllBackendPids();
/* Sort the PID array so we can use bsearch */
if (live_pids[0] > 1)
qsort((void *) &live_pids[1], live_pids[0], sizeof(int),
comparePids);
}
/*
@ -2706,7 +2720,13 @@ pgstat_read_statsfile(HTAB **dbhash, Oid onlydb,
/*
* If possible, check PID to verify still running
*/
if (check_pids && !IsBackendPid(beentry->procpid))
if (live_pids &&
(live_pids[0] == 0 ||
bsearch((void *) &beentry->procpid,
(void *) &live_pids[1],
live_pids[0],
sizeof(int),
comparePids) == NULL))
{
/*
* Note: we could send a BETERM message to tell the