Re: Change default of checkpoint_completion_target

Hi,

On 2020-12-08 12:41:35 -0500, Tom Lane wrote:
> FWIW, I kind of like the idea of getting rid of it completely.
> Is there really ever a good reason to set it to something different
> than that?  If not, well, we have too many GUCs already, and each
> of them carries nonzero performance, documentation, and maintenance
> overhead.

I like the idea of getting rid of it too, but I think we should consider
evaluating the concrete hard-coded value a bit more careful than just
going for 0.9 based on some old recommendations in the docs. It not
being changeable afterwards...

I think it might be a good idea to immediately change the default to
0.9, and concurrently try to evaluate whether it's really the best value
(vs 0.95, 1 or ...).

FWIW I have seen a few cases in the past where setting the target to
something very small helped, but I think that was mostly because we
didn't yet tell the kernel to flush dirty data more aggressively.

Greetings,

Andres Freund