> On Fri, Feb 25, 2022 at 04:19:27PM +0100, Magnus Hagander wrote: > On Fri, Feb 25, 2022 at 2:33 PM Julien Rouhaud <rjuju...@gmail.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..
Indeed, sounds convenient, although I wonder how exactly one would use it to tune JIT? I'm curious, because I got used to situations when one single long query takes much longer than expected due to JIT issues -- but it seems the target of this patch are situations when there are a lot of long queries using JIT, and it's easier to analyze them via pgss? > > > 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 One interesting not-very-relevant for the patch thing I've noticed while reading it, is that there seems to be no way to find out what fraction of time jit_tuple_deforming is taking alone, it's sort of merged together with jit_expressions in generation_counter.