Re: Expose JIT counters/timing in pg_stat_statements

On Fri, Feb 25, 2022 at 2:33 PM Julien Rouhaud <rjuju123(at)gmail(dot)com> wrote:
>
> Hi,
>
> On Fri, Feb 25, 2022 at 02:06:29PM +0100, Magnus Hagander wrote:
> > Here's a patch to add the sum of timings for JIT counters to
> > pg_stat_statements, as a way to follow-up on if JIT is doing a good or
> > a bad job in a configuration.
>
> +1, it seems like something quite useful.

Given the amount of time often spent debugging JIT -- getting more
insight is going to make it easier to tune it instead of like what
unfortunately many people do and just turn it off..

> > I decided to only store the total time for the timings, since there
> > are 4 different timings and storing max/min/etc for each one of them
> > would lead to a bit too much data. This can of course be reconsidered,
> > but I think that's a reasonable tradeoff.
>
> I think the cumulated total time is enough. Looking at the patch, I think we
> should also cumulate the number of time jit was triggered, and
> probably the same for each other main operation (optimization and inlining).
> Otherwise the values may be wrong and look artificially low.

So just to be clear, you're basically thinking:

jit_count = count of entries where jit_functions>0
jit_functions = <same as now>
jit_optimizatinos = count of entries where time spent on jit_optimizations > 0

etc?

So we count the times with min/max like other times for the total one,
but instead add a counter for each of the details?

--
Magnus Hagander
Me: https://www.hagander.net/
Work: https://www.redpill-linpro.com/