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Commit7890a42

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Fix performance regression from session statistics.
Session statistics, as introduced by960869d, had several shortcomings:- an additional GetCurrentTimestamp() call that also impaired the accuracy of the data collected This can be avoided by passing the current timestamp we already have in pgstat_report_stat().- an additional statistics UDP packet sent every 500ms This is solved by adding the new statistics to PgStat_MsgTabstat. This is conceptually ugly, because session statistics are not table statistics. But the struct already contains data unrelated to tables, so there is not much damage done. Connection and disconnection are reported in separate messages, which reduces the number of additional messages to two messages per session and a slight increase in PgStat_MsgTabstat size (but the same number of table stats fit).- Session time computation could overflow on systems where long is 32 bit.Reported-By: Andres Freund <andres@anarazel.de>Author: Andres Freund <andres@anarazel.de>Author: Laurenz Albe <laurenz.albe@cybertec.at>Discussion:https://postgr.es/m/20210801205501.nyxzxoelqoo4x2qc%40alap3.anarazel.deBackpatch: 14-, where the feature was introduced.
1 parent92a8d76 commit7890a42

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5 files changed

+158
-80
lines changed

5 files changed

+158
-80
lines changed

‎src/backend/postmaster/pgstat.c‎

Lines changed: 129 additions & 66 deletions
Original file line numberDiff line numberDiff line change
@@ -244,6 +244,7 @@ static intpgStatXactCommit = 0;
244244
staticintpgStatXactRollback=0;
245245
PgStat_CounterpgStatBlockReadTime=0;
246246
PgStat_CounterpgStatBlockWriteTime=0;
247+
staticPgStat_CounterpgLastSessionReportTime=0;
247248
PgStat_CounterpgStatActiveTime=0;
248249
PgStat_CounterpgStatTransactionIdleTime=0;
249250
SessionEndTypepgStatSessionEndCause=DISCONNECT_NORMAL;
@@ -319,11 +320,12 @@ static bool pgstat_db_requested(Oid databaseid);
319320
staticPgStat_StatReplSlotEntry*pgstat_get_replslot_entry(NameDataname,boolcreate_it);
320321
staticvoidpgstat_reset_replslot(PgStat_StatReplSlotEntry*slotstats,TimestampTzts);
321322

322-
staticvoidpgstat_send_tabstat(PgStat_MsgTabstat*tsmsg);
323+
staticvoidpgstat_send_tabstat(PgStat_MsgTabstat*tsmsg,TimestampTznow);
323324
staticvoidpgstat_send_funcstats(void);
324325
staticvoidpgstat_send_slru(void);
325326
staticHTAB*pgstat_collect_oids(Oidcatalogid,AttrNumberanum_oid);
326-
staticvoidpgstat_send_connstats(booldisconnect,TimestampTzlast_report);
327+
staticboolpgstat_should_report_connstat(void);
328+
staticvoidpgstat_report_disconnect(Oiddboid);
327329

328330
staticPgStat_TableStatus*get_tabstat_entry(Oidrel_id,boolisshared);
329331

@@ -353,7 +355,8 @@ static void pgstat_recv_funcpurge(PgStat_MsgFuncpurge *msg, int len);
353355
staticvoidpgstat_recv_recoveryconflict(PgStat_MsgRecoveryConflict*msg,intlen);
354356
staticvoidpgstat_recv_deadlock(PgStat_MsgDeadlock*msg,intlen);
355357
staticvoidpgstat_recv_checksum_failure(PgStat_MsgChecksumFailure*msg,intlen);
356-
staticvoidpgstat_recv_connstat(PgStat_MsgConn*msg,intlen);
358+
staticvoidpgstat_recv_connect(PgStat_MsgConnect*msg,intlen);
359+
staticvoidpgstat_recv_disconnect(PgStat_MsgDisconnect*msg,intlen);
357360
staticvoidpgstat_recv_replslot(PgStat_MsgReplSlot*msg,intlen);
358361
staticvoidpgstat_recv_tempfile(PgStat_MsgTempFile*msg,intlen);
359362

@@ -875,12 +878,11 @@ pgstat_report_stat(bool disconnect)
875878
!TimestampDifferenceExceeds(last_report,now,PGSTAT_STAT_INTERVAL))
876879
return;
877880

878-
/* for backends, send connection statistics */
879-
if (MyBackendType==B_BACKEND)
880-
pgstat_send_connstats(disconnect,last_report);
881-
882881
last_report=now;
883882

883+
if (disconnect)
884+
pgstat_report_disconnect(MyDatabaseId);
885+
884886
/*
885887
* Destroy pgStatTabHash before we start invalidating PgStat_TableEntry
886888
* entries it points to. (Should we fail partway through the loop below,
@@ -932,7 +934,7 @@ pgstat_report_stat(bool disconnect)
932934
sizeof(PgStat_TableCounts));
933935
if (++this_msg->m_nentries >=PGSTAT_NUM_TABENTRIES)
934936
{
935-
pgstat_send_tabstat(this_msg);
937+
pgstat_send_tabstat(this_msg,now);
936938
this_msg->m_nentries=0;
937939
}
938940
}
@@ -944,13 +946,14 @@ pgstat_report_stat(bool disconnect)
944946

945947
/*
946948
* Send partial messages. Make sure that any pending xact commit/abort
947-
* gets counted, even if there are no table stats to send.
949+
* and connection stats get counted, even if there are no table stats to
950+
* send.
948951
*/
949952
if (regular_msg.m_nentries>0||
950-
pgStatXactCommit>0||pgStatXactRollback>0)
951-
pgstat_send_tabstat(&regular_msg);
953+
pgStatXactCommit>0||pgStatXactRollback>0||disconnect)
954+
pgstat_send_tabstat(&regular_msg,now);
952955
if (shared_msg.m_nentries>0)
953-
pgstat_send_tabstat(&shared_msg);
956+
pgstat_send_tabstat(&shared_msg,now);
954957

955958
/* Now, send function statistics */
956959
pgstat_send_funcstats();
@@ -966,7 +969,7 @@ pgstat_report_stat(bool disconnect)
966969
* Subroutine for pgstat_report_stat: finish and send a tabstat message
967970
*/
968971
staticvoid
969-
pgstat_send_tabstat(PgStat_MsgTabstat*tsmsg)
972+
pgstat_send_tabstat(PgStat_MsgTabstat*tsmsg,TimestampTznow)
970973
{
971974
intn;
972975
intlen;
@@ -985,17 +988,44 @@ pgstat_send_tabstat(PgStat_MsgTabstat *tsmsg)
985988
tsmsg->m_xact_rollback=pgStatXactRollback;
986989
tsmsg->m_block_read_time=pgStatBlockReadTime;
987990
tsmsg->m_block_write_time=pgStatBlockWriteTime;
991+
992+
if (pgstat_should_report_connstat())
993+
{
994+
longsecs;
995+
intusecs;
996+
997+
/*
998+
* pgLastSessionReportTime is initialized to MyStartTimestamp by
999+
* pgstat_report_connect().
1000+
*/
1001+
TimestampDifference(pgLastSessionReportTime,now,&secs,&usecs);
1002+
pgLastSessionReportTime=now;
1003+
tsmsg->m_session_time= (PgStat_Counter)secs*1000000+usecs;
1004+
tsmsg->m_active_time=pgStatActiveTime;
1005+
tsmsg->m_idle_in_xact_time=pgStatTransactionIdleTime;
1006+
}
1007+
else
1008+
{
1009+
tsmsg->m_session_time=0;
1010+
tsmsg->m_active_time=0;
1011+
tsmsg->m_idle_in_xact_time=0;
1012+
}
9881013
pgStatXactCommit=0;
9891014
pgStatXactRollback=0;
9901015
pgStatBlockReadTime=0;
9911016
pgStatBlockWriteTime=0;
1017+
pgStatActiveTime=0;
1018+
pgStatTransactionIdleTime=0;
9921019
}
9931020
else
9941021
{
9951022
tsmsg->m_xact_commit=0;
9961023
tsmsg->m_xact_rollback=0;
9971024
tsmsg->m_block_read_time=0;
9981025
tsmsg->m_block_write_time=0;
1026+
tsmsg->m_session_time=0;
1027+
tsmsg->m_active_time=0;
1028+
tsmsg->m_idle_in_xact_time=0;
9991029
}
10001030

10011031
n=tsmsg->m_nentries;
@@ -1363,49 +1393,6 @@ pgstat_drop_relation(Oid relid)
13631393
}
13641394
#endif/* NOT_USED */
13651395

1366-
1367-
/* ----------
1368-
* pgstat_send_connstats() -
1369-
*
1370-
*Tell the collector about session statistics.
1371-
*The parameter "disconnect" will be true when the backend exits.
1372-
*"last_report" is the last time we were called (0 if never).
1373-
* ----------
1374-
*/
1375-
staticvoid
1376-
pgstat_send_connstats(booldisconnect,TimestampTzlast_report)
1377-
{
1378-
PgStat_MsgConnmsg;
1379-
longsecs;
1380-
intusecs;
1381-
1382-
if (pgStatSock==PGINVALID_SOCKET|| !pgstat_track_counts)
1383-
return;
1384-
1385-
pgstat_setheader(&msg.m_hdr,PGSTAT_MTYPE_CONNECTION);
1386-
msg.m_databaseid=MyDatabaseId;
1387-
1388-
/* session time since the last report */
1389-
TimestampDifference(((last_report==0) ?MyStartTimestamp :last_report),
1390-
GetCurrentTimestamp(),
1391-
&secs,&usecs);
1392-
msg.m_session_time=secs*1000000+usecs;
1393-
1394-
msg.m_disconnect=disconnect ?pgStatSessionEndCause :DISCONNECT_NOT_YET;
1395-
1396-
msg.m_active_time=pgStatActiveTime;
1397-
pgStatActiveTime=0;
1398-
1399-
msg.m_idle_in_xact_time=pgStatTransactionIdleTime;
1400-
pgStatTransactionIdleTime=0;
1401-
1402-
/* report a new session only the first time */
1403-
msg.m_count= (last_report==0) ?1 :0;
1404-
1405-
pgstat_send(&msg,sizeof(PgStat_MsgConn));
1406-
}
1407-
1408-
14091396
/* ----------
14101397
* pgstat_reset_counters() -
14111398
*
@@ -1744,6 +1731,63 @@ pgstat_report_tempfile(size_t filesize)
17441731
pgstat_send(&msg,sizeof(msg));
17451732
}
17461733

1734+
/* --------
1735+
* pgstat_report_connect() -
1736+
*
1737+
*Tell the collector about a new connection.
1738+
* --------
1739+
*/
1740+
void
1741+
pgstat_report_connect(Oiddboid)
1742+
{
1743+
PgStat_MsgConnectmsg;
1744+
1745+
if (!pgstat_should_report_connstat())
1746+
return;
1747+
1748+
pgLastSessionReportTime=MyStartTimestamp;
1749+
1750+
pgstat_setheader(&msg.m_hdr,PGSTAT_MTYPE_CONNECT);
1751+
msg.m_databaseid=MyDatabaseId;
1752+
pgstat_send(&msg,sizeof(PgStat_MsgConnect));
1753+
}
1754+
1755+
/* --------
1756+
* pgstat_report_disconnect() -
1757+
*
1758+
*Tell the collector about a disconnect.
1759+
* --------
1760+
*/
1761+
staticvoid
1762+
pgstat_report_disconnect(Oiddboid)
1763+
{
1764+
PgStat_MsgDisconnectmsg;
1765+
1766+
if (!pgstat_should_report_connstat())
1767+
return;
1768+
1769+
pgstat_setheader(&msg.m_hdr,PGSTAT_MTYPE_DISCONNECT);
1770+
msg.m_databaseid=MyDatabaseId;
1771+
msg.m_cause=pgStatSessionEndCause;
1772+
pgstat_send(&msg,sizeof(PgStat_MsgDisconnect));
1773+
}
1774+
1775+
/* --------
1776+
* pgstat_should_report_connstats() -
1777+
*
1778+
*We report session statistics only for normal backend processes. Parallel
1779+
*workers run in parallel, so they don't contribute to session times, even
1780+
*though they use CPU time. Walsender processes could be considered here,
1781+
*but they have different session characteristics from normal backends (for
1782+
*example, they are always "active"), so they would skew session statistics.
1783+
* ----------
1784+
*/
1785+
staticbool
1786+
pgstat_should_report_connstat(void)
1787+
{
1788+
returnMyBackendType==B_BACKEND;
1789+
}
1790+
17471791
/* ----------
17481792
* pgstat_report_replslot() -
17491793
*
@@ -3363,8 +3407,12 @@ PgstatCollectorMain(int argc, char *argv[])
33633407
pgstat_recv_replslot(&msg.msg_replslot,len);
33643408
break;
33653409

3366-
casePGSTAT_MTYPE_CONNECTION:
3367-
pgstat_recv_connstat(&msg.msg_conn,len);
3410+
casePGSTAT_MTYPE_CONNECT:
3411+
pgstat_recv_connect(&msg.msg_connect,len);
3412+
break;
3413+
3414+
casePGSTAT_MTYPE_DISCONNECT:
3415+
pgstat_recv_disconnect(&msg.msg_disconnect,len);
33683416
break;
33693417

33703418
default:
@@ -4785,6 +4833,10 @@ pgstat_recv_tabstat(PgStat_MsgTabstat *msg, int len)
47854833
dbentry->n_block_read_time+=msg->m_block_read_time;
47864834
dbentry->n_block_write_time+=msg->m_block_write_time;
47874835

4836+
dbentry->total_session_time+=msg->m_session_time;
4837+
dbentry->total_active_time+=msg->m_active_time;
4838+
dbentry->total_idle_in_xact_time+=msg->m_idle_in_xact_time;
4839+
47884840
/*
47894841
* Process all table entries in the message.
47904842
*/
@@ -5434,23 +5486,34 @@ pgstat_recv_replslot(PgStat_MsgReplSlot *msg, int len)
54345486
}
54355487

54365488
/* ----------
5437-
*pgstat_recv_connstat() -
5489+
*pgstat_recv_connect() -
54385490
*
5439-
*Processconnection information.
5491+
*Processa CONNECT message.
54405492
* ----------
54415493
*/
54425494
staticvoid
5443-
pgstat_recv_connstat(PgStat_MsgConn*msg,intlen)
5495+
pgstat_recv_connect(PgStat_MsgConnect*msg,intlen)
54445496
{
54455497
PgStat_StatDBEntry*dbentry;
54465498

54475499
dbentry=pgstat_get_db_entry(msg->m_databaseid, true);
5500+
dbentry->n_sessions++;
5501+
}
54485502

5449-
dbentry->n_sessions+=msg->m_count;
5450-
dbentry->total_session_time+=msg->m_session_time;
5451-
dbentry->total_active_time+=msg->m_active_time;
5452-
dbentry->total_idle_in_xact_time+=msg->m_idle_in_xact_time;
5453-
switch (msg->m_disconnect)
5503+
/* ----------
5504+
* pgstat_recv_disconnect() -
5505+
*
5506+
*Process a DISCONNECT message.
5507+
* ----------
5508+
*/
5509+
staticvoid
5510+
pgstat_recv_disconnect(PgStat_MsgDisconnect*msg,intlen)
5511+
{
5512+
PgStat_StatDBEntry*dbentry;
5513+
5514+
dbentry=pgstat_get_db_entry(msg->m_databaseid, true);
5515+
5516+
switch (msg->m_cause)
54545517
{
54555518
caseDISCONNECT_NOT_YET:
54565519
caseDISCONNECT_NORMAL:

‎src/backend/tcop/postgres.c‎

Lines changed: 2 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -4108,6 +4108,8 @@ PostgresMain(int argc, char *argv[],
41084108
if (IsUnderPostmaster&&Log_disconnections)
41094109
on_proc_exit(log_disconnections,0);
41104110

4111+
pgstat_report_connect(MyDatabaseId);
4112+
41114113
/* Perform initialization specific to a WAL sender process. */
41124114
if (am_walsender)
41134115
InitWalSender();

‎src/backend/utils/activity/backend_status.c‎

Lines changed: 2 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -590,9 +590,9 @@ pgstat_report_activity(BackendState state, const char *cmd_str)
590590

591591
if (beentry->st_state==STATE_RUNNING||
592592
beentry->st_state==STATE_FASTPATH)
593-
pgstat_count_conn_active_time(secs*1000000+usecs);
593+
pgstat_count_conn_active_time((PgStat_Counter)secs*1000000+usecs);
594594
else
595-
pgstat_count_conn_txn_idle_time(secs*1000000+usecs);
595+
pgstat_count_conn_txn_idle_time((PgStat_Counter)secs*1000000+usecs);
596596
}
597597

598598
/*

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