Em sáb., 18 de mai. de 2024 às 15:52, Andrey M. Borodin <x4mmm@yandex-team.ru> escreveu:
Hi!
In a thread about sorting comparators[0] Andres noted that we have infrastructure to help compiler optimize sorting. PFA attached PoC implementation. I've checked that it indeed works on the benchmark from that thread.
postgres=# CREATE TABLE arrays_to_sort AS SELECT array_shuffle(a) arr FROM (SELECT ARRAY(SELECT generate_series(1, 1000000)) a), generate_series(1, 10);
postgres=# SELECT (sort(arr))[1] FROM arrays_to_sort; -- original Time: 990.199 ms postgres=# SELECT (sort(arr))[1] FROM arrays_to_sort; -- patched Time: 696.156 ms
The benefit seems to be on the order of magnitude with 30% speedup.
There's plenty of sorting by TransactionId, BlockNumber, OffsetNumber, Oid etc. But this sorting routines never show up in perf top or something like that.
Seems like in most cases we do not spend much time in sorting. But specialization does not cost us much too, only some CPU cycles of a compiler. I think we can further improve speedup by converting inline comparator to value extractor: more compilers will see what is actually going on. But I have no proofs for this reasoning.
What do you think?
Makes sense.
Regarding the patch. You could change the style to:
