| From: | "Andrey M(dot) Borodin" <x4mmm(at)yandex-team(dot)ru> |
|---|---|
| To: | Ilia Evdokimov <ilya(dot)evdokimov(at)tantorlabs(dot)com> |
| Cc: | Sami Imseih <samimseih(at)gmail(dot)com>, Alexander Korotkov <aekorotkov(at)gmail(dot)com>, Michael Paquier <michael(at)paquier(dot)xyz>, Greg Sabino Mullane <htamfids(at)gmail(dot)com>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Sample rate added to pg_stat_statements |
| Date: | 2025-01-07 14:15:22 |
| Message-ID: | 9D8A5BC8-A3A5-4DA9-9382-F30D343247D1@yandex-team.ru |
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| Lists: | pgsql-hackers |
> On 7 Jan 2025, at 16:05, Ilia Evdokimov <ilya(dot)evdokimov(at)tantorlabs(dot)com> wrote:
>
>> 1. This code seems a little different from your patch. It is trying to avoid engaging PRNG. I'm not sure it's a good idea, but still. Also, it uses "<=", not "<".
>>
>> xact_is_sampled = log_xact_sample_rate != 0 &&
>> (log_xact_sample_rate == 1 ||
>> pg_prng_double(&pg_global_prng_state) <= log_xact_sample_rate);
>>
> Are we sure we're discussing the same patch? Because these remarks refer to the 5 version of the patch, which I abandoned due to your remarks.
Yes. v6 has this code
+ if (nesting_level == 0)
+ current_query_sampled = (pg_prng_double(&pg_global_prng_state) < pgss_sample_rate);
while upstream has code that I cited. And logic is slightly different.
Best regards, Andrey Borodin.
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