Re: Log notice that checkpoint is to be written on shutdown

Am Freitag, den 03.10.2014, 12:07 -0300 schrieb Alvaro Herrera:
> Michael Banck wrote:
> > diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
> > index 5a4dbb9..f2716ae 100644
> > --- a/src/backend/access/transam/xlog.c
> > +++ b/src/backend/access/transam/xlog.c
> > @@ -8085,10 +8085,14 @@ CreateCheckPoint(int flags)
> >
> > /*
> > * If enabled, log checkpoint start. We postpone this until now so as not
> > - * to log anything if we decided to skip the checkpoint.
> > + * to log anything if we decided to skip the checkpoint. If we are during
> > + * shutdown and checkpoints are not being logged, add a log message that a
> > + * checkpoint is to be written and shutdown is potentially delayed.
> > */
> > if (log_checkpoints)
> > LogCheckpointStart(flags, false);
> > + else if (shutdown)
> > + ereport(LOG, (errmsg("waiting for checkpoint ...")));
> >
> > TRACE_POSTGRESQL_CHECKPOINT_START(flags);
>
> I think if we're going to emit log messages for shutdown checkpoints, we
> ought to use the same format we already have, i.e. instead of having the
> separate "waiting for checkpoint" message, just test "log_checkpoints ||
> shutdown", then LogCheckpointStart.

I considered this at first, but the rationale is that if somebody sets
log_checkpoints = off, they probably don't want the actual checkpoint to
be logged, so just a note that a checkpoint is happening was better
(Christoph Berg pointed this out). If there is consensus that forcing
this one-time checkpoint logging is fine, I can change the patch
accordingly.

> And for consistency also make sure
> that the checkpoint end log line is also reported on shutdown
> checkpoints regardless of log_checkpoints.

I did this in an earlier draft of the patch, but AIUI this either
requires some refactoring to not evaluate log_checkpoints inside
LogCheckpointEnd(), and/or to change the function signature of
LogCheckpointEnd() to include either the `flags' bitfield or the
`shutdown' bool in order to force logging of the finished checkpoint
even if log_checkpoints is set to `off'.

Cheers,

Michael

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Michael Banck
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