From 97903c3d94b6d6ce089c90c34c1000653007b020 Mon Sep 17 00:00:00 2001
From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Thu, 11 Jan 2007 23:06:03 +0000
Subject: [PATCH] Fix a performance problem in databases with large numbers of
tables (or other types of pg_class entry): the function
pgstat_vacuum_tabstat, invoked during VACUUM startup, had runtime
proportional to the number of stats table entries times the number of
pg_class rows; in other words O(N^2) if the stats collector's information is
reasonably complete. Replace list searching with a hash table to bring it
back to O(N) behavior. Per report from kim at myemma.com.
Back-patch as far as 8.1; 8.0 and before use different coding here.
---
src/backend/postmaster/pgstat.c | 87 ++++++++++++++++++++++-----------
1 file changed, 59 insertions(+), 28 deletions(-)
diff --git a/src/backend/postmaster/pgstat.c b/src/backend/postmaster/pgstat.c
index 8cdc5f6aa91..97c11d0fb00 100644
--- a/src/backend/postmaster/pgstat.c
+++ b/src/backend/postmaster/pgstat.c
@@ -13,7 +13,7 @@
*
* Copyright (c) 2001-2007, PostgreSQL Global Development Group
*
- * $PostgreSQL: pgsql/src/backend/postmaster/pgstat.c,v 1.142 2007/01/05 22:19:36 momjian Exp $
+ * $PostgreSQL: pgsql/src/backend/postmaster/pgstat.c,v 1.143 2007/01/11 23:06:03 tgl Exp $
* ----------
*/
#include "postgres.h"
@@ -159,6 +159,7 @@ static void pgstat_write_statsfile(void);
static void pgstat_read_statsfile(HTAB **dbhash, Oid onlydb);
static void backend_read_statsfile(void);
static void pgstat_read_current_status(void);
+static HTAB *pgstat_collect_oids(Oid catalogid);
static void pgstat_setheader(PgStat_MsgHdr *hdr, StatMsgType mtype);
static void pgstat_send(void *msg, int len);
@@ -657,10 +658,7 @@ pgstat_report_tabstat(void)
void
pgstat_vacuum_tabstat(void)
{
- List *oidlist;
- Relation rel;
- HeapScanDesc scan;
- HeapTuple tup;
+ HTAB *htab;
PgStat_MsgTabpurge msg;
HASH_SEQ_STATUS hstat;
PgStat_StatDBEntry *dbentry;
@@ -679,15 +677,7 @@ pgstat_vacuum_tabstat(void)
/*
* Read pg_database and make a list of OIDs of all existing databases
*/
- oidlist = NIL;
- rel = heap_open(DatabaseRelationId, AccessShareLock);
- scan = heap_beginscan(rel, SnapshotNow, 0, NULL);
- while ((tup = heap_getnext(scan, ForwardScanDirection)) != NULL)
- {
- oidlist = lappend_oid(oidlist, HeapTupleGetOid(tup));
- }
- heap_endscan(scan);
- heap_close(rel, AccessShareLock);
+ htab = pgstat_collect_oids(DatabaseRelationId);
/*
* Search the database hash table for dead databases and tell the
@@ -698,12 +688,14 @@ pgstat_vacuum_tabstat(void)
{
Oid dbid = dbentry->databaseid;
- if (!list_member_oid(oidlist, dbid))
+ CHECK_FOR_INTERRUPTS();
+
+ if (hash_search(htab, (void *) &dbid, HASH_FIND, NULL) == NULL)
pgstat_drop_database(dbid);
}
/* Clean up */
- list_free(oidlist);
+ hash_destroy(htab);
/*
* Lookup our own database entry; if not found, nothing more to do.
@@ -717,15 +709,7 @@ pgstat_vacuum_tabstat(void)
/*
* Similarly to above, make a list of all known relations in this DB.
*/
- oidlist = NIL;
- rel = heap_open(RelationRelationId, AccessShareLock);
- scan = heap_beginscan(rel, SnapshotNow, 0, NULL);
- while ((tup = heap_getnext(scan, ForwardScanDirection)) != NULL)
- {
- oidlist = lappend_oid(oidlist, HeapTupleGetOid(tup));
- }
- heap_endscan(scan);
- heap_close(rel, AccessShareLock);
+ htab = pgstat_collect_oids(RelationRelationId);
/*
* Initialize our messages table counter to zero
@@ -738,13 +722,17 @@ pgstat_vacuum_tabstat(void)
hash_seq_init(&hstat, dbentry->tables);
while ((tabentry = (PgStat_StatTabEntry *) hash_seq_search(&hstat)) != NULL)
{
- if (list_member_oid(oidlist, tabentry->tableid))
+ Oid tabid = tabentry->tableid;
+
+ CHECK_FOR_INTERRUPTS();
+
+ if (hash_search(htab, (void *) &tabid, HASH_FIND, NULL) != NULL)
continue;
/*
* Not there, so add this table's Oid to the message
*/
- msg.m_tableid[msg.m_nentries++] = tabentry->tableid;
+ msg.m_tableid[msg.m_nentries++] = tabid;
/*
* If the message is full, send it out and reinitialize to empty
@@ -776,7 +764,50 @@ pgstat_vacuum_tabstat(void)
}
/* Clean up */
- list_free(oidlist);
+ hash_destroy(htab);
+}
+
+
+/* ----------
+ * pgstat_collect_oids() -
+ *
+ * Collect the OIDs of either all databases or all tables, according to
+ * the parameter, into a temporary hash table. Caller should hash_destroy
+ * the result when done with it.
+ * ----------
+ */
+static HTAB *
+pgstat_collect_oids(Oid catalogid)
+{
+ HTAB *htab;
+ HASHCTL hash_ctl;
+ Relation rel;
+ HeapScanDesc scan;
+ HeapTuple tup;
+
+ memset(&hash_ctl, 0, sizeof(hash_ctl));
+ hash_ctl.keysize = sizeof(Oid);
+ hash_ctl.entrysize = sizeof(Oid);
+ hash_ctl.hash = oid_hash;
+ htab = hash_create("Temporary table of OIDs",
+ PGSTAT_TAB_HASH_SIZE,
+ &hash_ctl,
+ HASH_ELEM | HASH_FUNCTION);
+
+ rel = heap_open(catalogid, AccessShareLock);
+ scan = heap_beginscan(rel, SnapshotNow, 0, NULL);
+ while ((tup = heap_getnext(scan, ForwardScanDirection)) != NULL)
+ {
+ Oid thisoid = HeapTupleGetOid(tup);
+
+ CHECK_FOR_INTERRUPTS();
+
+ (void) hash_search(htab, (void *) &thisoid, HASH_ENTER, NULL);
+ }
+ heap_endscan(scan);
+ heap_close(rel, AccessShareLock);
+
+ return htab;
}
--
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