Re: Add Information during standby recovery conflicts

On Mon, 10 Aug 2020 at 23:43, Drouvot, Bertrand <bdrouvot(at)amazon(dot)com> wrote:
>
> Hi,
>
> On 7/31/20 7:12 AM, Masahiko Sawada wrote:
> > + tmpWaitlist = waitlist;
> > + while (VirtualTransactionIdIsValid(*tmpWaitlist))
> > + {
> > + tmpWaitlist++;
> > + }
> > +
> > + num_waitlist_entries = (tmpWaitlist - waitlist);
> > +
> > + /* display wal record information */
> > + if (log_recovery_conflicts &&
> > (TimestampDifferenceExceeds(recovery_conflicts_log_time,
> > GetCurrentTimestamp(),
> > + DeadlockTimeout))) {
> > + LogBlockedWalRecordInfo(num_waitlist_entries, reason);
> > + recovery_conflicts_log_time = GetCurrentTimestamp();
> > + }
> >
> > recovery_conflicts_log_time is not initialized. And shouldn't we
> > compare the current timestamp to the timestamp when the startup
> > process started waiting?
> >
> > I think we should call LogBlockedWalRecordInfo() inside of the inner
> > while loop rather than at the beginning of
> > ResolveRecoveryConflictWithVirtualXIDs(). In lock conflict cases, the
> > startup process waits until 'ltime', then enters
> > ResolveRecoveryConflictWithVirtualXIDs() after reaching 'ltime'.
> > Therefore, it makes sense to call LogBlockedWalRecordInfo() at the
> > beginning of ResolveRecoveryConflictWithVirtualXIDs(). However, in
> > snapshot and tablespace conflict cases (i.g.
> > ResolveRecoveryConflictWithSnapshot() and
> > ResolveRecoveryConflictWithTablespace()), it enters
> > ResolveRecoveryConflictWithVirtualXIDs() without waits and waits for
> > reaching ‘ltime’ inside of the inner while look. So the above
> > condition could always be false.
>
> That would make the information being displayed after
> max_standby_streaming_delay is reached for the multiple cases you just
> described.

Sorry, it should be deadlock_timeout, not max_standby_streaming_delay.
Otherwise, the recovery conflict log message is printed when
resolution, which seems not to achieve the original purpose. Am I
missing something?

Regards,

--
Masahiko Sawada http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services