On Wed, Feb 15, 2023 at 3:02 PM David Rowley <dgrowleyml(at)gmail(dot)com> wrote:
>
> On Wed, 15 Feb 2023 at 17:23, John Naylor <john(dot)naylor(at)enterprisedb(dot)com>
wrote:
> > HEAD:
> >
> > 4 ^ 8: latency average = 113.976 ms
> > 5 ^ 8: latency average = 783.830 ms
> > 6 ^ 8: latency average = 3990.351 ms
> > 7 ^ 8: latency average = 15793.629 ms
> >
> > Skip rechecking first key:
> >
> > 4 ^ 8: latency average = 107.028 ms
> > 5 ^ 8: latency average = 732.327 ms
> > 6 ^ 8: latency average = 3709.882 ms
> > 7 ^ 8: latency average = 14570.651 ms
> Yeah, just a hack. My intention with it was just to prove we had a
> problem because sometimes Sort -> Incremental Sort was faster than
> Sort. Ideally, with your change, we'd see that it's always faster to
> do the full sort in one go. It would be good to see your patch with
> and without the planner hack patch to ensure sort is now always faster
> than sort -> incremental sort.
Okay, here's a rerun including the sort hack, and it looks like incremental
sort is only ahead with the smallest set, otherwise same or maybe slightly
slower:
HEAD:
4 ^ 8: latency average = 113.461 ms
5 ^ 8: latency average = 786.080 ms
6 ^ 8: latency average = 3948.388 ms
7 ^ 8: latency average = 15733.348 ms
tiebreaker:
4 ^ 8: latency average = 106.556 ms
5 ^ 8: latency average = 734.834 ms
6 ^ 8: latency average = 3640.507 ms
7 ^ 8: latency average = 14470.199 ms
tiebreaker + incr sort hack:
4 ^ 8: latency average = 93.998 ms
5 ^ 8: latency average = 740.120 ms
6 ^ 8: latency average = 3715.942 ms
7 ^ 8: latency average = 14749.323 ms
And as far as this:
> I suspect that I fat-fingered work_mem yesterday, so next I'll pick a
badly-performing mod like 32, then range over work_mem and see if that
explains anything, especially whether L3 effects are in fact more important
in this workload.
Attached is a script and image for fixing the input at random / mod32 and
varying work_mem. There is not a whole lot of variation here: pushdown
regresses and the tiebreaker patch only helped marginally. I'm still not
sure why the results from yesterday looked better than today.
--
John Naylor
EDB: http://www.enterprisedb.com
