On Fri, Mar 21, 2025 at 02:45:09PM +0900, Michael Paquier wrote: > Potential ideas about optimizing the branches seem worth > investigating, I am not sure that I would be able to dig into that > until the feature freeze gong, unfortunately, and it would be nice to > fix this issue for this release. I'll see about doing some pgbench > runs on my side, as well, with tpc-b Querys.
So, here are some numbers with a "SELECT 1;" using pgbench, which would be a worst-case. Then, at 128 clients on a machine I have around: - HEAD, compute_query_id = on: tps = 282081.839715 tps = 281379.854539 tps = 283708.205096 tps = 280197.225782 #worst tps = 291955.914664 #best tps = 284172.351609 tps = 287234.624720 tps = 287915.683291 #best tps = 277004.123742 #worst tps = 281326.071323 - Patch, compute_query_id = on: tps = 289746.641246 #best tps = 279689.654196 tps = 284874.774620 #best tps = 282312.246610 tps = 275807.057758 #worst tps = 276058.858384 #worst tps = 282705.638685 tps = 282651.367641 tps = 276777.418569 tps = 283137.265298 Removing the two best and two worst numbers, taking an average as in: (head_tps - patch_tps) * 2 / (head_tps + patch_tps) Then that's 283317.15 (HEAD) vs 281212.26 (patch) so a 0.7% decrease. Still that could be claimed as noise. Second set, at 1 client, and a better pattern becomes available: - HEAD, compute_query_id = on: tps = 19170.473320 #best tps = 18722.828797 tps = 19138.765391 tps = 18243.611593 tps = 17878.605004 #worst tps = 19557.753327 #best tps = 18395.734885 tps = 18433.188326 tps = 18227.914138 #worst tps = 18450.236841 - Patch, compute_query_id = on: tps = 16611.766411 tps = 15992.734615 #worst tps = 16465.077482 tps = 16726.097318 tps = 17284.874897 #best tps = 16076.378905 tps = 17971.534072 #best tps = 15733.718159 #worst tps = 16911.014660 tps = 17217.202679 And here we get 18564.06 (head) vs 16667.92 (patch) so a 10.7% difference in this run. Hence the automatic addition of NULL to the jumbling is disappointing here, even if this is what I'd see this as a worst case scenario, unlikely what one would see for real if they care about monitoring. So, on the other hand, we still have the trick to switch the fields, which means that we would not suffer any performance penalty, while fixing the original issue. And with the feature freeze in sight, time is running short if we want to do something here. NB: In case, a second run with 1 client showing the same trend: - HEAD: tps = 19697.406181 tps = 19474.495729 tps = 18614.615630 tps = 18868.245926 tps = 18949.775164 tps = 18943.311921 tps = 18824.192383 tps = 19104.542301 tps = 18950.870646 tps = 19331.829745 - Patch: tps = 17887.864764 tps = 17317.628065 tps = 17090.278323 tps = 15876.258607 tps = 16818.644938 tps = 16816.334313 tps = 18134.148809 tps = 16891.809962 tps = 18193.104125 tps = 16866.726990 -- Michael
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