On Wed, Aug 29, 2018 at 1:50 PM Michael Paquier <michael@xxxxxxxxxxx> wrote:
On Wed, Aug 29, 2018 at 09:15:29AM -0700, Dave Peticolas wrote:
> Oh, perhaps I do, depending on what you mean by worker. There are a couple
> of periodic processes that connect to the server to obtain metrics. Is that
> what is triggering this issue? In my case I could probably suspend them
> until the replay has reached the desired point.
That would be it. How do you decide when those begin to run and connect
to Postgres. Do you use pg_isready or similar in a loop for sanity
checks?
I do not, they just try to connect and bail if they cannot.
> I have noticed this behavior in the past but prior to 9.6.10 restarting the
> server would fix the issue. And the replay always seemed to reach a point
> past which the problem would not re-occur.
You are picking my interest here. Did you actually see the same
problem? In 9.6.10 what happens is that I have tightened the consistent
point checks and logic so as inconsistent page issues would actually
show up when they should, and that those become reproducible so as we
can track down any rogue WAL record or inconsistent behavior.
Yes, I've seen this problem occasionally in the past. I think only in the 9.6 series. But before 9.6.10, if I restarted the server it would start replaying WAL again and typically when it reached the point where it PANICed before, instead it would report a consistent state and allow read-only connections. Sometimes it would then PANIC again after more WAL was replayed. But eventually it would reach a point where it seemed to be able to replay WAL indefinitely without the issue happening.
dave
