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Commit37a9aa6

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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 parentdc89914 commit37a9aa6

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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
@@ -246,6 +246,7 @@ static intpgStatXactCommit = 0;
246246
staticintpgStatXactRollback=0;
247247
PgStat_CounterpgStatBlockReadTime=0;
248248
PgStat_CounterpgStatBlockWriteTime=0;
249+
staticPgStat_CounterpgLastSessionReportTime=0;
249250
PgStat_CounterpgStatActiveTime=0;
250251
PgStat_CounterpgStatTransactionIdleTime=0;
251252
SessionEndTypepgStatSessionEndCause=DISCONNECT_NORMAL;
@@ -330,11 +331,12 @@ static bool pgstat_db_requested(Oid databaseid);
330331
staticPgStat_StatReplSlotEntry*pgstat_get_replslot_entry(NameDataname,boolcreate_it);
331332
staticvoidpgstat_reset_replslot(PgStat_StatReplSlotEntry*slotstats,TimestampTzts);
332333

333-
staticvoidpgstat_send_tabstat(PgStat_MsgTabstat*tsmsg);
334+
staticvoidpgstat_send_tabstat(PgStat_MsgTabstat*tsmsg,TimestampTznow);
334335
staticvoidpgstat_send_funcstats(void);
335336
staticvoidpgstat_send_slru(void);
336337
staticHTAB*pgstat_collect_oids(Oidcatalogid,AttrNumberanum_oid);
337-
staticvoidpgstat_send_connstats(booldisconnect,TimestampTzlast_report);
338+
staticboolpgstat_should_report_connstat(void);
339+
staticvoidpgstat_report_disconnect(Oiddboid);
338340

339341
staticPgStat_TableStatus*get_tabstat_entry(Oidrel_id,boolisshared);
340342

@@ -366,7 +368,8 @@ static void pgstat_recv_funcpurge(PgStat_MsgFuncpurge *msg, int len);
366368
staticvoidpgstat_recv_recoveryconflict(PgStat_MsgRecoveryConflict*msg,intlen);
367369
staticvoidpgstat_recv_deadlock(PgStat_MsgDeadlock*msg,intlen);
368370
staticvoidpgstat_recv_checksum_failure(PgStat_MsgChecksumFailure*msg,intlen);
369-
staticvoidpgstat_recv_connstat(PgStat_MsgConn*msg,intlen);
371+
staticvoidpgstat_recv_connect(PgStat_MsgConnect*msg,intlen);
372+
staticvoidpgstat_recv_disconnect(PgStat_MsgDisconnect*msg,intlen);
370373
staticvoidpgstat_recv_replslot(PgStat_MsgReplSlot*msg,intlen);
371374
staticvoidpgstat_recv_tempfile(PgStat_MsgTempFile*msg,intlen);
372375

@@ -890,12 +893,11 @@ pgstat_report_stat(bool disconnect)
890893
!TimestampDifferenceExceeds(last_report,now,PGSTAT_STAT_INTERVAL))
891894
return;
892895

893-
/* for backends, send connection statistics */
894-
if (MyBackendType==B_BACKEND)
895-
pgstat_send_connstats(disconnect,last_report);
896-
897896
last_report=now;
898897

898+
if (disconnect)
899+
pgstat_report_disconnect(MyDatabaseId);
900+
899901
/*
900902
* Destroy pgStatTabHash before we start invalidating PgStat_TableEntry
901903
* entries it points to. (Should we fail partway through the loop below,
@@ -947,7 +949,7 @@ pgstat_report_stat(bool disconnect)
947949
sizeof(PgStat_TableCounts));
948950
if (++this_msg->m_nentries >=PGSTAT_NUM_TABENTRIES)
949951
{
950-
pgstat_send_tabstat(this_msg);
952+
pgstat_send_tabstat(this_msg,now);
951953
this_msg->m_nentries=0;
952954
}
953955
}
@@ -959,13 +961,14 @@ pgstat_report_stat(bool disconnect)
959961

960962
/*
961963
* Send partial messages. Make sure that any pending xact commit/abort
962-
* gets counted, even if there are no table stats to send.
964+
* and connection stats get counted, even if there are no table stats to
965+
* send.
963966
*/
964967
if (regular_msg.m_nentries>0||
965-
pgStatXactCommit>0||pgStatXactRollback>0)
966-
pgstat_send_tabstat(&regular_msg);
968+
pgStatXactCommit>0||pgStatXactRollback>0||disconnect)
969+
pgstat_send_tabstat(&regular_msg,now);
967970
if (shared_msg.m_nentries>0)
968-
pgstat_send_tabstat(&shared_msg);
971+
pgstat_send_tabstat(&shared_msg,now);
969972

970973
/* Now, send function statistics */
971974
pgstat_send_funcstats();
@@ -981,7 +984,7 @@ pgstat_report_stat(bool disconnect)
981984
* Subroutine for pgstat_report_stat: finish and send a tabstat message
982985
*/
983986
staticvoid
984-
pgstat_send_tabstat(PgStat_MsgTabstat*tsmsg)
987+
pgstat_send_tabstat(PgStat_MsgTabstat*tsmsg,TimestampTznow)
985988
{
986989
intn;
987990
intlen;
@@ -1000,17 +1003,44 @@ pgstat_send_tabstat(PgStat_MsgTabstat *tsmsg)
10001003
tsmsg->m_xact_rollback=pgStatXactRollback;
10011004
tsmsg->m_block_read_time=pgStatBlockReadTime;
10021005
tsmsg->m_block_write_time=pgStatBlockWriteTime;
1006+
1007+
if (pgstat_should_report_connstat())
1008+
{
1009+
longsecs;
1010+
intusecs;
1011+
1012+
/*
1013+
* pgLastSessionReportTime is initialized to MyStartTimestamp by
1014+
* pgstat_report_connect().
1015+
*/
1016+
TimestampDifference(pgLastSessionReportTime,now,&secs,&usecs);
1017+
pgLastSessionReportTime=now;
1018+
tsmsg->m_session_time= (PgStat_Counter)secs*1000000+usecs;
1019+
tsmsg->m_active_time=pgStatActiveTime;
1020+
tsmsg->m_idle_in_xact_time=pgStatTransactionIdleTime;
1021+
}
1022+
else
1023+
{
1024+
tsmsg->m_session_time=0;
1025+
tsmsg->m_active_time=0;
1026+
tsmsg->m_idle_in_xact_time=0;
1027+
}
10031028
pgStatXactCommit=0;
10041029
pgStatXactRollback=0;
10051030
pgStatBlockReadTime=0;
10061031
pgStatBlockWriteTime=0;
1032+
pgStatActiveTime=0;
1033+
pgStatTransactionIdleTime=0;
10071034
}
10081035
else
10091036
{
10101037
tsmsg->m_xact_commit=0;
10111038
tsmsg->m_xact_rollback=0;
10121039
tsmsg->m_block_read_time=0;
10131040
tsmsg->m_block_write_time=0;
1041+
tsmsg->m_session_time=0;
1042+
tsmsg->m_active_time=0;
1043+
tsmsg->m_idle_in_xact_time=0;
10141044
}
10151045

10161046
n=tsmsg->m_nentries;
@@ -1378,49 +1408,6 @@ pgstat_drop_relation(Oid relid)
13781408
}
13791409
#endif/* NOT_USED */
13801410

1381-
1382-
/* ----------
1383-
* pgstat_send_connstats() -
1384-
*
1385-
*Tell the collector about session statistics.
1386-
*The parameter "disconnect" will be true when the backend exits.
1387-
*"last_report" is the last time we were called (0 if never).
1388-
* ----------
1389-
*/
1390-
staticvoid
1391-
pgstat_send_connstats(booldisconnect,TimestampTzlast_report)
1392-
{
1393-
PgStat_MsgConnmsg;
1394-
longsecs;
1395-
intusecs;
1396-
1397-
if (pgStatSock==PGINVALID_SOCKET|| !pgstat_track_counts)
1398-
return;
1399-
1400-
pgstat_setheader(&msg.m_hdr,PGSTAT_MTYPE_CONNECTION);
1401-
msg.m_databaseid=MyDatabaseId;
1402-
1403-
/* session time since the last report */
1404-
TimestampDifference(((last_report==0) ?MyStartTimestamp :last_report),
1405-
GetCurrentTimestamp(),
1406-
&secs,&usecs);
1407-
msg.m_session_time=secs*1000000+usecs;
1408-
1409-
msg.m_disconnect=disconnect ?pgStatSessionEndCause :DISCONNECT_NOT_YET;
1410-
1411-
msg.m_active_time=pgStatActiveTime;
1412-
pgStatActiveTime=0;
1413-
1414-
msg.m_idle_in_xact_time=pgStatTransactionIdleTime;
1415-
pgStatTransactionIdleTime=0;
1416-
1417-
/* report a new session only the first time */
1418-
msg.m_count= (last_report==0) ?1 :0;
1419-
1420-
pgstat_send(&msg,sizeof(PgStat_MsgConn));
1421-
}
1422-
1423-
14241411
/* ----------
14251412
* pgstat_reset_counters() -
14261413
*
@@ -1759,6 +1746,63 @@ pgstat_report_tempfile(size_t filesize)
17591746
pgstat_send(&msg,sizeof(msg));
17601747
}
17611748

1749+
/* --------
1750+
* pgstat_report_connect() -
1751+
*
1752+
*Tell the collector about a new connection.
1753+
* --------
1754+
*/
1755+
void
1756+
pgstat_report_connect(Oiddboid)
1757+
{
1758+
PgStat_MsgConnectmsg;
1759+
1760+
if (!pgstat_should_report_connstat())
1761+
return;
1762+
1763+
pgLastSessionReportTime=MyStartTimestamp;
1764+
1765+
pgstat_setheader(&msg.m_hdr,PGSTAT_MTYPE_CONNECT);
1766+
msg.m_databaseid=MyDatabaseId;
1767+
pgstat_send(&msg,sizeof(PgStat_MsgConnect));
1768+
}
1769+
1770+
/* --------
1771+
* pgstat_report_disconnect() -
1772+
*
1773+
*Tell the collector about a disconnect.
1774+
* --------
1775+
*/
1776+
staticvoid
1777+
pgstat_report_disconnect(Oiddboid)
1778+
{
1779+
PgStat_MsgDisconnectmsg;
1780+
1781+
if (!pgstat_should_report_connstat())
1782+
return;
1783+
1784+
pgstat_setheader(&msg.m_hdr,PGSTAT_MTYPE_DISCONNECT);
1785+
msg.m_databaseid=MyDatabaseId;
1786+
msg.m_cause=pgStatSessionEndCause;
1787+
pgstat_send(&msg,sizeof(PgStat_MsgDisconnect));
1788+
}
1789+
1790+
/* --------
1791+
* pgstat_should_report_connstats() -
1792+
*
1793+
*We report session statistics only for normal backend processes. Parallel
1794+
*workers run in parallel, so they don't contribute to session times, even
1795+
*though they use CPU time. Walsender processes could be considered here,
1796+
*but they have different session characteristics from normal backends (for
1797+
*example, they are always "active"), so they would skew session statistics.
1798+
* ----------
1799+
*/
1800+
staticbool
1801+
pgstat_should_report_connstat(void)
1802+
{
1803+
returnMyBackendType==B_BACKEND;
1804+
}
1805+
17621806
/* ----------
17631807
* pgstat_report_replslot() -
17641808
*
@@ -3465,8 +3509,12 @@ PgstatCollectorMain(int argc, char *argv[])
34653509
pgstat_recv_replslot(&msg.msg_replslot,len);
34663510
break;
34673511

3468-
casePGSTAT_MTYPE_CONNECTION:
3469-
pgstat_recv_connstat(&msg.msg_conn,len);
3512+
casePGSTAT_MTYPE_CONNECT:
3513+
pgstat_recv_connect(&msg.msg_connect,len);
3514+
break;
3515+
3516+
casePGSTAT_MTYPE_DISCONNECT:
3517+
pgstat_recv_disconnect(&msg.msg_disconnect,len);
34703518
break;
34713519

34723520
default:
@@ -4904,6 +4952,10 @@ pgstat_recv_tabstat(PgStat_MsgTabstat *msg, int len)
49044952
dbentry->n_block_read_time+=msg->m_block_read_time;
49054953
dbentry->n_block_write_time+=msg->m_block_write_time;
49064954

4955+
dbentry->total_session_time+=msg->m_session_time;
4956+
dbentry->total_active_time+=msg->m_active_time;
4957+
dbentry->total_idle_in_xact_time+=msg->m_idle_in_xact_time;
4958+
49074959
/*
49084960
* Process all table entries in the message.
49094961
*/
@@ -5568,23 +5620,34 @@ pgstat_recv_replslot(PgStat_MsgReplSlot *msg, int len)
55685620
}
55695621

55705622
/* ----------
5571-
*pgstat_recv_connstat() -
5623+
*pgstat_recv_connect() -
55725624
*
5573-
*Processconnection information.
5625+
*Processa CONNECT message.
55745626
* ----------
55755627
*/
55765628
staticvoid
5577-
pgstat_recv_connstat(PgStat_MsgConn*msg,intlen)
5629+
pgstat_recv_connect(PgStat_MsgConnect*msg,intlen)
55785630
{
55795631
PgStat_StatDBEntry*dbentry;
55805632

55815633
dbentry=pgstat_get_db_entry(msg->m_databaseid, true);
5634+
dbentry->n_sessions++;
5635+
}
55825636

5583-
dbentry->n_sessions+=msg->m_count;
5584-
dbentry->total_session_time+=msg->m_session_time;
5585-
dbentry->total_active_time+=msg->m_active_time;
5586-
dbentry->total_idle_in_xact_time+=msg->m_idle_in_xact_time;
5587-
switch (msg->m_disconnect)
5637+
/* ----------
5638+
* pgstat_recv_disconnect() -
5639+
*
5640+
*Process a DISCONNECT message.
5641+
* ----------
5642+
*/
5643+
staticvoid
5644+
pgstat_recv_disconnect(PgStat_MsgDisconnect*msg,intlen)
5645+
{
5646+
PgStat_StatDBEntry*dbentry;
5647+
5648+
dbentry=pgstat_get_db_entry(msg->m_databaseid, true);
5649+
5650+
switch (msg->m_cause)
55885651
{
55895652
caseDISCONNECT_NOT_YET:
55905653
caseDISCONNECT_NORMAL:

‎src/backend/tcop/postgres.c

Lines changed: 2 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -4116,6 +4116,8 @@ PostgresMain(int argc, char *argv[],
41164116
if (IsUnderPostmaster&&Log_disconnections)
41174117
on_proc_exit(log_disconnections,0);
41184118

4119+
pgstat_report_connect(MyDatabaseId);
4120+
41194121
/* Perform initialization specific to a WAL sender process. */
41204122
if (am_walsender)
41214123
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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