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Commitf9dbac9

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HS Defer buffer pin deadlock check until deadlock_timeout has expired.
During Hot Standby we need to check for buffer pin deadlocks when theStartup process begins to wait, in case it never wakes up again. Wepreviously made the deadlock check immediately on the basis it wascheap, though clearer thinking and prima facie evidence shows thatwas too simple. Refactor existing code to make it easy to add indeferral of deadlock check until deadlock_timeout allowing a goodreduction in deadlock checks since far few buffer pins are held forthat duration. It's worth doing anyway, though major goal is toprevent further reports of context switching with high numbers ofusers on occasional tests.
1 parent5234a95 commitf9dbac9

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3 files changed

+107
-52
lines changed

3 files changed

+107
-52
lines changed

‎src/backend/storage/ipc/standby.c

Lines changed: 15 additions & 27 deletions
Original file line numberDiff line numberDiff line change
@@ -11,7 +11,7 @@
1111
* Portions Copyright (c) 1994, Regents of the University of California
1212
*
1313
* IDENTIFICATION
14-
* $PostgreSQL: pgsql/src/backend/storage/ipc/standby.c,v 1.23 2010/05/14 07:11:49 sriggs Exp $
14+
* $PostgreSQL: pgsql/src/backend/storage/ipc/standby.c,v 1.24 2010/05/26 19:52:52 sriggs Exp $
1515
*
1616
*-------------------------------------------------------------------------
1717
*/
@@ -388,12 +388,15 @@ ResolveRecoveryConflictWithBufferPin(void)
388388
}
389389
elseif (MaxStandbyDelay<0)
390390
{
391+
TimestampTznow=GetCurrentTimestamp();
392+
391393
/*
392-
* Send out a request to check for buffer pin deadlocks before we
393-
* wait. This is fairly cheap, so no need to wait for deadlock timeout
394-
* before trying to send it out.
394+
* Set timeout for deadlock check (only)
395395
*/
396-
SendRecoveryConflictWithBufferPin(PROCSIG_RECOVERY_CONFLICT_STARTUP_DEADLOCK);
396+
if (enable_standby_sig_alarm(now,now, true))
397+
sig_alarm_enabled= true;
398+
else
399+
elog(FATAL,"could not set timer for process wakeup");
397400
}
398401
else
399402
{
@@ -410,34 +413,19 @@ ResolveRecoveryConflictWithBufferPin(void)
410413
}
411414
else
412415
{
413-
TimestampTzfin_time;/* Expected wake-up time by timer */
414-
longtimer_delay_secs;/* Amount of time we set timer
415-
* for */
416-
inttimer_delay_usecs;
417-
418-
/*
419-
* Send out a request to check for buffer pin deadlocks before we
420-
* wait. This is fairly cheap, so no need to wait for deadlock
421-
* timeout before trying to send it out.
422-
*/
423-
SendRecoveryConflictWithBufferPin(PROCSIG_RECOVERY_CONFLICT_STARTUP_DEADLOCK);
416+
TimestampTzmax_standby_time;
424417

425418
/*
426-
*How much longerweshould wait?
419+
*At what point in the future dowehit MaxStandbyDelay?
427420
*/
428-
fin_time=TimestampTzPlusMilliseconds(then,MaxStandbyDelay);
429-
430-
TimestampDifference(now,fin_time,
431-
&timer_delay_secs,&timer_delay_usecs);
421+
max_standby_time=TimestampTzPlusMilliseconds(then,MaxStandbyDelay);
422+
Assert(max_standby_time>now);
432423

433424
/*
434-
*It's possible that the difference is less than a microsecond;
435-
*ensure wedon't cancel, ratherthanset, the interrupt.
425+
*Wake up at MaxStandby delay, and check for deadlocks as well
426+
*if wewill be waiting longerthandeadlock_timeout
436427
*/
437-
if (timer_delay_secs==0&&timer_delay_usecs==0)
438-
timer_delay_usecs=1;
439-
440-
if (enable_standby_sig_alarm(timer_delay_secs,timer_delay_usecs,fin_time))
428+
if (enable_standby_sig_alarm(now,max_standby_time, false))
441429
sig_alarm_enabled= true;
442430
else
443431
elog(FATAL,"could not set timer for process wakeup");

‎src/backend/storage/lmgr/proc.c

Lines changed: 89 additions & 23 deletions
Original file line numberDiff line numberDiff line change
@@ -8,7 +8,7 @@
88
*
99
*
1010
* IDENTIFICATION
11-
* $PostgreSQL: pgsql/src/backend/storage/lmgr/proc.c,v 1.218 2010/04/28 16:54:16 tgl Exp $
11+
* $PostgreSQL: pgsql/src/backend/storage/lmgr/proc.c,v 1.219 2010/05/26 19:52:52 sriggs Exp $
1212
*
1313
*-------------------------------------------------------------------------
1414
*/
@@ -85,6 +85,7 @@ static TimestampTz timeout_start_time;
8585

8686
/* statement_fin_time is valid only if statement_timeout_active is true */
8787
staticTimestampTzstatement_fin_time;
88+
staticTimestampTzstatement_fin_time2;/* valid only in recovery */
8889

8990

9091
staticvoidRemoveProcFromArray(intcode,Datumarg);
@@ -1619,23 +1620,61 @@ handle_sig_alarm(SIGNAL_ARGS)
16191620
* To avoid various edge cases, we must be careful to do nothing
16201621
* when there is nothing to be done. We also need to be able to
16211622
* reschedule the timer interrupt if called before end of statement.
1623+
*
1624+
* We set either deadlock_timeout_active or statement_timeout_active
1625+
* or both. Interrupts are enabled if standby_timeout_active.
16221626
*/
16231627
bool
1624-
enable_standby_sig_alarm(longdelay_s,intdelay_us,TimestampTzfin_time)
1628+
enable_standby_sig_alarm(TimestampTznow,TimestampTzfin_time,booldeadlock_only)
16251629
{
1626-
structitimervaltimeval;
1627-
1628-
Assert(delay_s >=0&&delay_us >=0);
1630+
TimestampTzdeadlock_time=TimestampTzPlusMilliseconds(now,DeadlockTimeout);
16291631

1630-
statement_fin_time=fin_time;
1632+
if (deadlock_only)
1633+
{
1634+
/*
1635+
* Wake up at DeadlockTimeout only, then wait forever
1636+
*/
1637+
statement_fin_time=deadlock_time;
1638+
deadlock_timeout_active= true;
1639+
statement_timeout_active= false;
1640+
}
1641+
elseif (fin_time>deadlock_time)
1642+
{
1643+
/*
1644+
* Wake up at DeadlockTimeout, then again at MaxStandbyDelay
1645+
*/
1646+
statement_fin_time=deadlock_time;
1647+
statement_fin_time2=fin_time;
1648+
deadlock_timeout_active= true;
1649+
statement_timeout_active= true;
1650+
}
1651+
else
1652+
{
1653+
/*
1654+
* Wake only at MaxStandbyDelay because its fairly soon
1655+
*/
1656+
statement_fin_time=fin_time;
1657+
deadlock_timeout_active= false;
1658+
statement_timeout_active= true;
1659+
}
16311660

1632-
standby_timeout_active= true;
1661+
if (deadlock_timeout_active||statement_timeout_active)
1662+
{
1663+
longsecs;
1664+
intusecs;
1665+
structitimervaltimeval;
1666+
TimestampDifference(now,statement_fin_time,
1667+
&secs,&usecs);
1668+
if (secs==0&&usecs==0)
1669+
usecs=1;
1670+
MemSet(&timeval,0,sizeof(structitimerval));
1671+
timeval.it_value.tv_sec=secs;
1672+
timeval.it_value.tv_usec=usecs;
1673+
if (setitimer(ITIMER_REAL,&timeval,NULL))
1674+
return false;
1675+
standby_timeout_active= true;
1676+
}
16331677

1634-
MemSet(&timeval,0,sizeof(structitimerval));
1635-
timeval.it_value.tv_sec=delay_s;
1636-
timeval.it_value.tv_usec=delay_us;
1637-
if (setitimer(ITIMER_REAL,&timeval,NULL))
1638-
return false;
16391678
return true;
16401679
}
16411680

@@ -1675,37 +1714,64 @@ static bool
16751714
CheckStandbyTimeout(void)
16761715
{
16771716
TimestampTznow;
1717+
boolreschedule= false;
16781718

16791719
standby_timeout_active= false;
16801720

16811721
now=GetCurrentTimestamp();
16821722

1723+
/*
1724+
* Reschedule the timer if its not time to wake yet, or if we
1725+
* have both timers set and the first one has just been reached.
1726+
*/
16831727
if (now >=statement_fin_time)
1684-
SendRecoveryConflictWithBufferPin(PROCSIG_RECOVERY_CONFLICT_BUFFERPIN);
1728+
{
1729+
if (deadlock_timeout_active)
1730+
{
1731+
/*
1732+
* We're still waiting when we reach DeadlockTimeout, so send out a request
1733+
* to have other backends check themselves for deadlock. Then continue
1734+
* waiting until MaxStandbyDelay.
1735+
*/
1736+
SendRecoveryConflictWithBufferPin(PROCSIG_RECOVERY_CONFLICT_STARTUP_DEADLOCK);
1737+
deadlock_timeout_active= false;
1738+
1739+
/*
1740+
* Begin second waiting period to MaxStandbyDelay if required.
1741+
*/
1742+
if (statement_timeout_active)
1743+
{
1744+
reschedule= true;
1745+
statement_fin_time=statement_fin_time2;
1746+
}
1747+
}
1748+
else
1749+
{
1750+
/*
1751+
* We've now reached MaxStandbyDelay, so ask all conflicts to leave, cos
1752+
* its time for us to press ahead with applying changes in recovery.
1753+
*/
1754+
SendRecoveryConflictWithBufferPin(PROCSIG_RECOVERY_CONFLICT_BUFFERPIN);
1755+
}
1756+
}
16851757
else
1758+
reschedule= true;
1759+
1760+
if (reschedule)
16861761
{
1687-
/* Not time yet, so (re)schedule the interrupt */
16881762
longsecs;
16891763
intusecs;
16901764
structitimervaltimeval;
1691-
16921765
TimestampDifference(now,statement_fin_time,
16931766
&secs,&usecs);
1694-
1695-
/*
1696-
* It's possible that the difference is less than a microsecond;
1697-
* ensure we don't cancel, rather than set, the interrupt.
1698-
*/
16991767
if (secs==0&&usecs==0)
17001768
usecs=1;
1701-
1702-
standby_timeout_active= true;
1703-
17041769
MemSet(&timeval,0,sizeof(structitimerval));
17051770
timeval.it_value.tv_sec=secs;
17061771
timeval.it_value.tv_usec=usecs;
17071772
if (setitimer(ITIMER_REAL,&timeval,NULL))
17081773
return false;
1774+
standby_timeout_active= true;
17091775
}
17101776

17111777
return true;

‎src/include/storage/proc.h

Lines changed: 3 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -7,7 +7,7 @@
77
* Portions Copyright (c) 1996-2010, PostgreSQL Global Development Group
88
* Portions Copyright (c) 1994, Regents of the University of California
99
*
10-
* $PostgreSQL: pgsql/src/include/storage/proc.h,v 1.121 2010/02/2602:01:27 momjian Exp $
10+
* $PostgreSQL: pgsql/src/include/storage/proc.h,v 1.122 2010/05/2619:52:52 sriggs Exp $
1111
*
1212
*-------------------------------------------------------------------------
1313
*/
@@ -199,7 +199,8 @@ extern bool enable_sig_alarm(int delayms, bool is_statement_timeout);
199199
externbooldisable_sig_alarm(boolis_statement_timeout);
200200
externvoidhandle_sig_alarm(SIGNAL_ARGS);
201201

202-
externboolenable_standby_sig_alarm(longdelay_s,intdelay_us,TimestampTzfin_time);
202+
externboolenable_standby_sig_alarm(TimestampTznow,
203+
TimestampTzfin_time,booldeadlock_only);
203204
externbooldisable_standby_sig_alarm(void);
204205
externvoidhandle_standby_sig_alarm(SIGNAL_ARGS);
205206

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