From fb3dbdf986f0ab56e0a5177966bb0dec1f93444c Mon Sep 17 00:00:00 2001 From: Tom Lane <tgl@sss.pgh.pa.us> Date: Fri, 16 Dec 2005 04:03:40 +0000 Subject: [PATCH] Rethink prior patch to filter out dead backend entries from the pgstats 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). --- src/backend/postmaster/pgstat.c | 30 +++++++++++++++++++---- src/backend/storage/ipc/procarray.c | 38 ++++++++++++++++++++++++++++- src/include/storage/procarray.h | 3 ++- 3 files changed, 64 insertions(+), 7 deletions(-) diff --git a/src/backend/postmaster/pgstat.c b/src/backend/postmaster/pgstat.c index 82cf1bc4ef..ae20a3bb71 100644 --- a/src/backend/postmaster/pgstat.c +++ b/src/backend/postmaster/pgstat.c @@ -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 diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c index cafadeb905..f633080748 100644 --- a/src/backend/storage/ipc/procarray.c +++ b/src/backend/storage/ipc/procarray.c @@ -23,7 +23,7 @@ * * * IDENTIFICATION - * $PostgreSQL: pgsql/src/backend/storage/ipc/procarray.c,v 1.9 2005/12/11 21:02:18 tgl Exp $ + * $PostgreSQL: pgsql/src/backend/storage/ipc/procarray.c,v 1.10 2005/12/16 04:03:40 tgl Exp $ * *------------------------------------------------------------------------- */ @@ -732,6 +732,42 @@ IsBackendPid(int pid) return (BackendPidGetProc(pid) != NULL); } +/* + * GetAllBackendPids -- get an array of all current backends' PIDs + * + * The result is a palloc'd array with the number of active backends in + * entry [0], their PIDs in entries [1] .. [n]. The caller must bear in + * mind that the result may already be obsolete when returned. + */ +int * +GetAllBackendPids(void) +{ + int *result; + int npids; + ProcArrayStruct *arrayP = procArray; + int index; + + result = (int *) palloc((MaxBackends + 1) * sizeof(int)); + npids = 0; + + LWLockAcquire(ProcArrayLock, LW_SHARED); + + for (index = 0; index < arrayP->numProcs; index++) + { + PGPROC *proc = arrayP->procs[index]; + + if (proc->pid != 0) /* ignore dummy procs */ + result[++npids] = proc->pid; + } + + LWLockRelease(ProcArrayLock); + + Assert(npids <= MaxBackends); + + result[0] = npids; + return result; +} + /* * CountActiveBackends --- count backends (other than myself) that are in * active transactions. This is used as a heuristic to decide if diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h index 68c615afc6..61441bbf49 100644 --- a/src/include/storage/procarray.h +++ b/src/include/storage/procarray.h @@ -7,7 +7,7 @@ * Portions Copyright (c) 1996-2005, PostgreSQL Global Development Group * Portions Copyright (c) 1994, Regents of the University of California * - * $PostgreSQL: pgsql/src/include/storage/procarray.h,v 1.6 2005/10/15 02:49:46 momjian Exp $ + * $PostgreSQL: pgsql/src/include/storage/procarray.h,v 1.7 2005/12/16 04:03:40 tgl Exp $ * *------------------------------------------------------------------------- */ @@ -29,6 +29,7 @@ extern TransactionId GetOldestXmin(bool allDbs); extern PGPROC *BackendPidGetProc(int pid); extern int BackendXidGetPid(TransactionId xid); extern bool IsBackendPid(int pid); +extern int *GetAllBackendPids(void); extern bool DatabaseHasActiveBackends(Oid databaseId, bool ignoreMyself); extern int CountActiveBackends(void); -- 2.24.1