Re: [HACKERS] Logging idle checkpoints

On Tue, Oct 3, 2017 at 12:01 AM, Stephen Frost <sfrost@snowman.net> wrote:
> 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.

Being able to look at how many checkpoints are skipped can be used as
a tuning indicator of max_wal_size and checkpoint_timeout, or in short
increase them if those remain idle. Since their introduction in
335feca4, m_timed_checkpoints and m_requested_checkpoints track the
number of checkpoint requests, not if a checkpoint has been actually
executed or not, I am not sure that this should be changed after 10
years. So, to put it in other words, wouldn't we want a way to track
checkpoints that are *executed*, meaning that we could increment a
counter after doing the skip checks in CreateRestartPoint() and
CreateCheckPoint()?
-- 
Michael


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