Re: Optimizing nbtree ScalarArrayOp execution, allowing multi-column ordered scans, skip scan

On 11/21/23 03:52, Peter Geoghegan wrote:
> On Sat, Nov 11, 2023 at 1:08 PM Matthias van de Meent
> <boekewurm+postgres@gmail.com> wrote:
>> Thanks. Here's my review of the btree-related code:
> 
> Attached is v7.
> 

I haven't looked at the code, but I decided to do a bit of blackbox perf
and stress testing, to get some feeling of what to expect in terms of
performance improvements, and see if there happen to be some unexpected
regressions. Attached is a couple simple bash scripts doing a
brute-force test with tables of different size / data distribution,
number of values in the SAOP expression, etc.

And a PDF visualizing the comparing the results between master and build
with the patch applied. First group of columns is master, then patched,
and then (patched/master) comparison, with green=faster, red=slower. The
columns are for different number of values in the SAOP condition.

Overall, the results look pretty good, with consistent speedups of up to
~30% for large number of values (SAOP with 1000 elements). There's a
couple blips where the performance regresses, also by up to ~30%. It's
too regular to be a random variation (it affects different combinations
of parameters, tablesizes), but it seems to only affect one of the two
machines I used for testing. Interestingly enough, it's the newer one.

I'm not convinced this is a problem we have to solve. It's possible it
only affects cases that are implausible in practice (the script forces a
particular scan type, and maybe it would not be picked in practice). But
maybe it's fixable ...


regards

-- 
Tomas Vondra
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