Re: Wait events for delayed checkpoints

On Wed, Oct 11, 2023 at 9:13 PM Thomas Munro <thomas.munro@gmail.com> wrote:
> You can't tell if your checkpointer is spending a lot of time waiting
> around for flags in delayChkptFlags to clear.  Trivial patch to add
> that.  I've managed to see it a few times when checkpointing
> repeatedly with a heavy pgbench workload.
>
> I had to stop and think for a moment about whether these events belong
> under "WaitEventIPC", "waiting for notification from another process"
> or under "WaitEventTimeout", "waiting for a timeout to expire".  I
> mean, both?  It's using sleep-and-poll instead of (say) a CV due to
> the economics, we want to make the other side as cheap as possible, so
> we don't care about making the checkpointer take some micro-naps in
> this case.  I feel like the key point here is that it's waiting for
> another process to do stuff and unblock it.

IPC seems right to me. Yeah, a timeout is being used, but as you say,
that's an implementation detail.

+1 for the idea, too.

-- 
Robert Haas
EDB: http://www.enterprisedb.com