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HS Defer buffer pin deadlock check until deadlock_timeout has expired.

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During Hot Standby we need to check for buffer pin deadlocks when the
Startup process begins to wait, in case it never wakes up again. We
previously made the deadlock check immediately on the basis it was
cheap, though clearer thinking and prima facie evidence shows that
was too simple. Refactor existing code to make it easy to add in
deferral of deadlock check until deadlock_timeout allowing a good
reduction in deadlock checks since far few buffer pins are held for
that duration. It's worth doing anyway, though major goal is to
prevent further reports of context switching with high numbers of
users on occasional tests.
This commit is contained in:
Simon Riggs
2010-05-26 19:52:52 +00:00
parent 5234a95245
commit f9dbac9476
3 changed files with 108 additions and 53 deletions
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114
src/backend/storage/lmgr/proc.c
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@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/storage/lmgr/proc.c,v 1.218 2010/04/28 16:54:16 tgl Exp $
* $PostgreSQL: pgsql/src/backend/storage/lmgr/proc.c,v 1.219 2010/05/26 19:52:52 sriggs Exp $
*
*-------------------------------------------------------------------------
*/
@ -85,6 +85,7 @@ static TimestampTz timeout_start_time;
/* statement_fin_time is valid only if statement_timeout_active is true */
static TimestampTz statement_fin_time;
static TimestampTz statement_fin_time2; /* valid only in recovery */
static void RemoveProcFromArray(int code, Datum arg);
@ -1619,23 +1620,61 @@ handle_sig_alarm(SIGNAL_ARGS)
* To avoid various edge cases, we must be careful to do nothing
* when there is nothing to be done. We also need to be able to
* reschedule the timer interrupt if called before end of statement.
*
* We set either deadlock_timeout_active or statement_timeout_active
* or both. Interrupts are enabled if standby_timeout_active.
*/
bool
enable_standby_sig_alarm(long delay_s, int delay_us, TimestampTz fin_time)
enable_standby_sig_alarm(TimestampTz now, TimestampTz fin_time, bool deadlock_only)
{
struct itimerval timeval;
TimestampTz deadlock_time = TimestampTzPlusMilliseconds(now, DeadlockTimeout);
Assert(delay_s >= 0 && delay_us >= 0);
if (deadlock_only)
{
/*
* Wake up at DeadlockTimeout only, then wait forever
*/
statement_fin_time = deadlock_time;
deadlock_timeout_active = true;
statement_timeout_active = false;
}
else if (fin_time > deadlock_time)
{
/*
* Wake up at DeadlockTimeout, then again at MaxStandbyDelay
*/
statement_fin_time = deadlock_time;
statement_fin_time2 = fin_time;
deadlock_timeout_active = true;
statement_timeout_active = true;
}
else
{
/*
* Wake only at MaxStandbyDelay because its fairly soon
*/
statement_fin_time = fin_time;
deadlock_timeout_active = false;
statement_timeout_active = true;
}
statement_fin_time = fin_time;
if (deadlock_timeout_active || statement_timeout_active)
{
long secs;
int usecs;
struct itimerval timeval;
TimestampDifference(now, statement_fin_time,
&secs, &usecs);
if (secs == 0 && usecs == 0)
usecs = 1;
MemSet(&timeval, 0, sizeof(struct itimerval));
timeval.it_value.tv_sec = secs;
timeval.it_value.tv_usec = usecs;
if (setitimer(ITIMER_REAL, &timeval, NULL))
return false;
standby_timeout_active = true;
}
standby_timeout_active = true;
MemSet(&timeval, 0, sizeof(struct itimerval));
timeval.it_value.tv_sec = delay_s;
timeval.it_value.tv_usec = delay_us;
if (setitimer(ITIMER_REAL, &timeval, NULL))
return false;
return true;
}
@ -1675,37 +1714,64 @@ static bool
CheckStandbyTimeout(void)
{
TimestampTz now;
bool reschedule = false;
standby_timeout_active = false;
now = GetCurrentTimestamp();
/*
* Reschedule the timer if its not time to wake yet, or if we
* have both timers set and the first one has just been reached.
*/
if (now >= statement_fin_time)
SendRecoveryConflictWithBufferPin(PROCSIG_RECOVERY_CONFLICT_BUFFERPIN);
else
{
/* Not time yet, so (re)schedule the interrupt */
if (deadlock_timeout_active)
{
/*
* We're still waiting when we reach DeadlockTimeout, so send out a request
* to have other backends check themselves for deadlock. Then continue
* waiting until MaxStandbyDelay.
*/
SendRecoveryConflictWithBufferPin(PROCSIG_RECOVERY_CONFLICT_STARTUP_DEADLOCK);
deadlock_timeout_active = false;
/*
* Begin second waiting period to MaxStandbyDelay if required.
*/
if (statement_timeout_active)
{
reschedule = true;
statement_fin_time = statement_fin_time2;
}
}
else
{
/*
* We've now reached MaxStandbyDelay, so ask all conflicts to leave, cos
* its time for us to press ahead with applying changes in recovery.
*/
SendRecoveryConflictWithBufferPin(PROCSIG_RECOVERY_CONFLICT_BUFFERPIN);
}
}
else
reschedule = true;
if (reschedule)
{
long secs;
int usecs;
struct itimerval timeval;
TimestampDifference(now, statement_fin_time,
&secs, &usecs);
/*
* It's possible that the difference is less than a microsecond;
* ensure we don't cancel, rather than set, the interrupt.
*/
if (secs == 0 && usecs == 0)
usecs = 1;
standby_timeout_active = true;
MemSet(&timeval, 0, sizeof(struct itimerval));
timeval.it_value.tv_sec = secs;
timeval.it_value.tv_usec = usecs;
if (setitimer(ITIMER_REAL, &timeval, NULL))
return false;
standby_timeout_active = true;
}
return true;