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Commit11da4c6

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Adjust pgstat_initstats() to avoid repeated searches of the TabStat arrays
when a relation is opened multiple times in the same transaction. This isparticularly useful for system catalogs, which we may heap_open or index_openmany times in a transaction, and it doesn't really cost anything extra evenif the rel is touched but once. Motivated by study of an example from GregStark, in which pgstat_initstats() accounted for an unreasonably largefraction of the runtime.
1 parentca3d14f commit11da4c6

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1 file changed

+74
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‎src/backend/postmaster/pgstat.c

Lines changed: 74 additions & 53 deletions
Original file line numberDiff line numberDiff line change
@@ -13,7 +13,7 @@
1313
*
1414
*Copyright (c) 2001-2007, PostgreSQL Global Development Group
1515
*
16-
*$PostgreSQL: pgsql/src/backend/postmaster/pgstat.c,v 1.152 2007/03/30 18:34:55 mha Exp $
16+
*$PostgreSQL: pgsql/src/backend/postmaster/pgstat.c,v 1.153 2007/04/21 04:10:53 tgl Exp $
1717
* ----------
1818
*/
1919
#include"postgres.h"
@@ -114,6 +114,14 @@ static bool pgStatRunningInCollector = false;
114114
* Place where backends store per-table info to be sent to the collector.
115115
* We store shared relations separately from non-shared ones, to be able to
116116
* send them in separate messages.
117+
*
118+
* NOTE: once allocated, a PgStat_MsgTabstat struct belonging to a
119+
* TabStatArray is never moved or deleted for the life of the backend.
120+
* Also, we zero out the t_id fields of the contained PgStat_TableEntry
121+
* structs whenever they are not actively in use. This allows PgStat_Info
122+
* pointers to be treated as long-lived data, avoiding repeated searches in
123+
* pgstat_initstats() when a relation is repeatedly heap_open'd or
124+
* index_open'd during a transaction.
117125
*/
118126
typedefstructTabStatArray
119127
{
@@ -169,6 +177,7 @@ static void pgstat_write_statsfile(void);
169177
staticHTAB*pgstat_read_statsfile(Oidonlydb);
170178
staticvoidbackend_read_statsfile(void);
171179
staticvoidpgstat_read_current_status(void);
180+
staticvoidpgstat_report_one_tabstat(TabStatArray*tsarr,Oiddbid);
172181
staticHTAB*pgstat_collect_oids(Oidcatalogid);
173182

174183
staticvoidpgstat_setup_memcxt(void);
@@ -606,25 +615,22 @@ void allow_immediate_pgstat_restart(void)
606615
void
607616
pgstat_report_tabstat(void)
608617
{
609-
inti;
610-
611-
if (pgStatSock<0||
612-
(!pgstat_collect_tuplelevel&&
613-
!pgstat_collect_blocklevel))
614-
{
615-
/* Not reporting stats, so just flush whatever we have */
616-
RegularTabStat.tsa_used=0;
617-
SharedTabStat.tsa_used=0;
618-
return;
619-
}
620-
621618
/*
622619
* For each message buffer used during the last query set the header
623-
* fields and send it out.
620+
* fields and send it out; then mark the entries unused.
624621
*/
625-
for (i=0;i<RegularTabStat.tsa_used;i++)
622+
pgstat_report_one_tabstat(&RegularTabStat,MyDatabaseId);
623+
pgstat_report_one_tabstat(&SharedTabStat,InvalidOid);
624+
}
625+
626+
staticvoid
627+
pgstat_report_one_tabstat(TabStatArray*tsarr,Oiddbid)
628+
{
629+
inti;
630+
631+
for (i=0;i<tsarr->tsa_used;i++)
626632
{
627-
PgStat_MsgTabstat*tsmsg=RegularTabStat.tsa_messages[i];
633+
PgStat_MsgTabstat*tsmsg=tsarr->tsa_messages[i];
628634
intn;
629635
intlen;
630636

@@ -637,32 +643,24 @@ pgstat_report_tabstat(void)
637643
pgStatXactCommit=0;
638644
pgStatXactRollback=0;
639645

640-
pgstat_setheader(&tsmsg->m_hdr,PGSTAT_MTYPE_TABSTAT);
641-
tsmsg->m_databaseid=MyDatabaseId;
642-
pgstat_send(tsmsg,len);
643-
}
644-
RegularTabStat.tsa_used=0;
645-
646-
/* Ditto, for shared relations */
647-
for (i=0;i<SharedTabStat.tsa_used;i++)
648-
{
649-
PgStat_MsgTabstat*tsmsg=SharedTabStat.tsa_messages[i];
650-
intn;
651-
intlen;
652-
653-
n=tsmsg->m_nentries;
654-
len= offsetof(PgStat_MsgTabstat,m_entry[0])+
655-
n*sizeof(PgStat_TableEntry);
656-
657-
/* We don't report transaction commit/abort here */
658-
tsmsg->m_xact_commit=0;
659-
tsmsg->m_xact_rollback=0;
646+
/*
647+
* It's unlikely we'd get here with no socket, but maybe not
648+
* impossible
649+
*/
650+
if (pgStatSock >=0)
651+
{
652+
pgstat_setheader(&tsmsg->m_hdr,PGSTAT_MTYPE_TABSTAT);
653+
tsmsg->m_databaseid=dbid;
654+
pgstat_send(tsmsg,len);
655+
}
660656

661-
pgstat_setheader(&tsmsg->m_hdr,PGSTAT_MTYPE_TABSTAT);
662-
tsmsg->m_databaseid=InvalidOid;
663-
pgstat_send(tsmsg,len);
657+
/*
658+
* Zero out the entries, to mark them unused and prepare them
659+
* for next use.
660+
*/
661+
MemSet(tsmsg,0,len);
664662
}
665-
SharedTabStat.tsa_used=0;
663+
tsarr->tsa_used=0;
666664
}
667665

668666

@@ -1013,7 +1011,7 @@ more_tabstat_space(TabStatArray *tsarr)
10131011

10141012
newAlloc=tsarr->tsa_alloc+TABSTAT_QUANTUM;
10151013

1016-
/* Create (another) quantum of message buffers */
1014+
/* Create (another) quantum of message buffers, and zero them */
10171015
newMessages= (PgStat_MsgTabstat*)
10181016
MemoryContextAllocZero(TopMemoryContext,
10191017
sizeof(PgStat_MsgTabstat)*TABSTAT_QUANTUM);
@@ -1043,6 +1041,17 @@ more_tabstat_space(TabStatArray *tsarr)
10431041
*of Relation or Scan structures. The data placed into these
10441042
*structures from here tell where later to count for buffer reads,
10451043
*scans and tuples fetched.
1044+
*
1045+
*NOTE: PgStat_Info pointers in scan structures are really redundant
1046+
*with those in relcache entries. The passed stats pointer might point
1047+
*either to the Relation struct's own pgstat_info field, or to one in
1048+
*a scan structure; we'll set the Relation pg_statinfo and copy it to
1049+
*the scan struct.
1050+
*
1051+
*We assume that a relcache entry's pgstat_info field is zeroed by
1052+
*relcache.c when the relcache entry is made; thereafter it is long-lived
1053+
*data. We can avoid repeated searches of the TabStat arrays when the
1054+
*same relation is touched repeatedly within a transaction.
10461055
* ----------
10471056
*/
10481057
void
@@ -1055,21 +1064,31 @@ pgstat_initstats(PgStat_Info *stats, Relation rel)
10551064
intmb;
10561065
inti;
10571066

1058-
/*
1059-
* Initialize data not to count at all.
1060-
*/
1061-
stats->tabentry=NULL;
1062-
10631067
if (pgStatSock<0||
10641068
!(pgstat_collect_tuplelevel||
10651069
pgstat_collect_blocklevel))
1070+
{
1071+
/* We're not counting at all. */
1072+
stats->tabentry=NULL;
10661073
return;
1074+
}
10671075

1068-
tsarr=rel->rd_rel->relisshared ?&SharedTabStat :&RegularTabStat;
1076+
/*
1077+
* If we already set up this relation in the current transaction,
1078+
* just copy the pointer.
1079+
*/
1080+
if (rel->pgstat_info.tabentry!=NULL&&
1081+
((PgStat_TableEntry*)rel->pgstat_info.tabentry)->t_id==rel_id)
1082+
{
1083+
stats->tabentry=rel->pgstat_info.tabentry;
1084+
return;
1085+
}
10691086

10701087
/*
10711088
* Search the already-used message slots for this relation.
10721089
*/
1090+
tsarr=rel->rd_rel->relisshared ?&SharedTabStat :&RegularTabStat;
1091+
10731092
for (mb=0;mb<tsarr->tsa_used;mb++)
10741093
{
10751094
tsmsg=tsarr->tsa_messages[mb];
@@ -1078,7 +1097,8 @@ pgstat_initstats(PgStat_Info *stats, Relation rel)
10781097
{
10791098
if (tsmsg->m_entry[i].t_id==rel_id)
10801099
{
1081-
stats->tabentry= (void*)&(tsmsg->m_entry[i]);
1100+
rel->pgstat_info.tabentry= (void*)&(tsmsg->m_entry[i]);
1101+
stats->tabentry=rel->pgstat_info.tabentry;
10821102
return;
10831103
}
10841104
}
@@ -1088,13 +1108,14 @@ pgstat_initstats(PgStat_Info *stats, Relation rel)
10881108

10891109
/*
10901110
* Not found, but found a message buffer with an empty slot instead.
1091-
* Fine, let's use this one.
1111+
* Fine, let's use this one. We assume the entry was already zeroed,
1112+
* either at creation or after last use.
10921113
*/
10931114
i=tsmsg->m_nentries++;
10941115
useent=&tsmsg->m_entry[i];
1095-
MemSet(useent,0,sizeof(PgStat_TableEntry));
10961116
useent->t_id=rel_id;
1097-
stats->tabentry= (void*)useent;
1117+
rel->pgstat_info.tabentry= (void*)useent;
1118+
stats->tabentry=rel->pgstat_info.tabentry;
10981119
return;
10991120
}
11001121

@@ -1111,9 +1132,9 @@ pgstat_initstats(PgStat_Info *stats, Relation rel)
11111132
tsmsg=tsarr->tsa_messages[mb];
11121133
tsmsg->m_nentries=1;
11131134
useent=&tsmsg->m_entry[0];
1114-
MemSet(useent,0,sizeof(PgStat_TableEntry));
11151135
useent->t_id=rel_id;
1116-
stats->tabentry= (void*)useent;
1136+
rel->pgstat_info.tabentry= (void*)useent;
1137+
stats->tabentry=rel->pgstat_info.tabentry;
11171138
}
11181139

11191140

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