Re: benchmark results comparing versions 15.2 and 16

Do you want me to try PG 16 without ICU or PG 15 with ICU?
I can do that, but it will take a few days before the server is available.

On Mon, May 29, 2023 at 9:55 AM Peter Geoghegan <pg(at)bowt(dot)ie> wrote:

> On Sun, May 28, 2023 at 2:42 PM David Rowley <dgrowleyml(at)gmail(dot)com> wrote:
> > c6e0fe1f2 might have helped improve some of that performance, but I
> > suspect there must be something else as ~3x seems much more than I'd
> > expect from reducing the memory overheads. Testing versions before
> > and after that commit might give a better indication.
>
> I'm virtually certain that this is due to the change in default
> collation provider, from libc to ICU. Mostly due to the fact that ICU
> is capable of using abbreviated keys, and the system libc isn't
> (unless you go out of your way to define TRUST_STRXFRM when building
> Postgres).
>
> Many individual test cases involving larger non-C collation text sorts
> showed similar improvements back when I worked on this. Offhand, I
> believe that 3x - 3.5x improvements in execution times were common
> with high entropy abbreviated keys on high cardinality input columns
> at that time (this was with glibc). Low cardinality inputs were more
> like 2.5x.
>
> I believe that ICU is faster than glibc in general -- even with
> TRUST_STRXFRM enabled. But the TRUST_STRXFRM thing is bound to be the
> most important factor here, by far.
>
> --
> Peter Geoghegan
>

--
Mark Callaghan
mdcallag(at)gmail(dot)com