Thread: Re: Has gen_random_uuid() gotten much slower in v17?
On 10.09.24 15:58, David Mullineux wrote: > I'm getting a bit concerned by the slow performance of generating uidds > on latest dev code versus older versions. Here I compare the time to > generate 50k random uuids. Both son the same machine. > I must be missing something. Are you sure that the 18devel installation isn't compiled with assertions enabled? The underlying code for gen_random_uuid() is virtually unchanged between PG14 and current.
Good idea. Thanks. I did check. It's not enabled by default but just in case I did another build. This time explicitly defining --disable-debug and --disable-cassert. And I tested. Still slower than old versions.
This feels like a build configuration problem. Just can't put my finger on it yet.
On Wed, 11 Sept 2024, 10:40 Peter Eisentraut, <peter@eisentraut.org> wrote:
On 10.09.24 15:58, David Mullineux wrote:
> I'm getting a bit concerned by the slow performance of generating uidds
> on latest dev code versus older versions. Here I compare the time to
> generate 50k random uuids. Both son the same machine.
> I must be missing something.
Are you sure that the 18devel installation isn't compiled with
assertions enabled?
The underlying code for gen_random_uuid() is virtually unchanged between
PG14 and current.
On 9/11/24 12:47, David Mullineux wrote:
> Good idea. Thanks. I did check. It's not enabled by default but just
> in case I did another build. This time explicitly defining --disable-
> debug and --disable-cassert. And I tested. Still slower than old versions.
>
4.5 seconds is very surprising.
on my machine:
postgres=# explain (analyze, costs off) select gen_random_uuid() from
generate_series(1, 50000);
QUERY PLAN
----------------------------------------------------------------------------------
Function Scan on generate_series (actual time=3.507..123.492
rows=50000 loops=1)
Planning Time: 0.031 ms
Execution Time: 125.481 ms
(3 rows)
postgres=# select version();
version
----------------------------------------------------------------------------------------------
PostgreSQL 18devel on x86_64-pc-linux-gnu, compiled by gcc (Debian
12.2.0-14) 12.2.0, 64-bit
pg_config | grep CONFIGURE
CONFIGURE = '--enable-cassert' '--enable-debug' '--with-python'
'CFLAGS=-ggdb -Og -g3 -fno-omit-frame-pointer' '--prefix'
'/postgres/pgenv/master'
> This feels like a build configuration problem. Just can't put my finger
> on it yet.
Why not using a profiler to see what's going on?
=?UTF-8?Q?Fr=C3=A9d=C3=A9ric_Yhuel?= <frederic.yhuel@dalibo.com> writes:
> On 9/11/24 12:47, David Mullineux wrote:
>> This feels like a build configuration problem. Just can't put my finger
>> on it yet.
> Why not using a profiler to see what's going on?
Yeah. Also, are you building with openssl, or not?
regards, tom lane
No, not at all!
On Wed, 20 Nov 2024, 15:46 Tom Lane, <tgl@sss.pgh.pa.us> wrote:
Frédéric Yhuel <frederic.yhuel@dalibo.com> writes:
> On 9/11/24 12:47, David Mullineux wrote:
>> This feels like a build configuration problem. Just can't put my finger
>> on it yet.
> Why not using a profiler to see what's going on?
Yeah. Also, are you building with openssl, or not?
regards, tom lane
[ please don't top-quote, it makes the conversation hard to follow ]
David Mullineux <dmullx@gmail.com> writes:
> On Wed, 20 Nov 2024, 15:46 Tom Lane, <tgl@sss.pgh.pa.us> wrote:
>> Yeah. Also, are you building with openssl, or not?
> No, not at all!
If you're not using openssl, then gen_random_uuid basically devolves
to a read of /dev/urandom. Maybe you're using a different kernel
than before, and it has different properties around that?
regards, tom lane