Re: Logging idle checkpoints

Vik, all,

* Vik Fearing (vik(dot)fearing(at)2ndquadrant(dot)com) wrote:
> I recently had a sad because I noticed that checkpoint counts were
> increasing in pg_stat_bgwriter, but weren't accounted for in my logs
> with log_checkpoints enabled.

> After some searching, I found that it was the idle checkpoints that
> weren't being logged. I think this is a missed trick in 6ef2eba3f57.

> Attached is a one-liner fix. I realize how imminent we are from
> releasing v10 but I hope there is still time for such a minor issue as this.

Idle checkpoints aren't, well, really checkpoints though. If anything,
seems like we shouldn't be including skipped checkpoints in the
pg_stat_bgwriter count because we aren't actually doing a checkpoint.

I certainly don't care for the idea of adding log messages saying we
aren't doing anything just to match a count that's incorrectly claiming
that checkpoints are happening when they aren't.

The down-thread suggestion of keeping track of skipped checkpoints might
be interesting, but I'm not entirely convinced it really is. We have
time to debate that, of course, but I don't really see how that's
helpful. At the moment, it seems like the suggestion to add that column
is based on the assumption that we're going to start logging skipped
checkpoints and having that column would allow us to match up the count
between the new column and the "skipped checkpoint" messages in the logs
and I can not help but feel that this is a ridiculous amount of effort
being put into the analysis of something that *didn't* happen.

Thanks!

Stephen