Re[4]: LISTEN/NOTIFY ultra slow speed - Mailing list pgsql-general
| From | Арсен Арутюнян |
|---|---|
| Subject | Re[4]: LISTEN/NOTIFY ultra slow speed |
| Date | |
| Msg-id | 1647377322.779959664@f422.i.mail.ru Whole thread Raw |
| In response to | Re: Re[2]: LISTEN/NOTIFY ultra slow speed (Tom Lane <tgl@sss.pgh.pa.us>) |
| Responses |
Re[5]: LISTEN/NOTIFY ultra slow speed
|
| List | pgsql-general |
I decided to rebuild pg 10 first.
I commented out the lines of code with duplicate checking
(/src/backend/commands/async.c)
// if (AsyncExistsPendingNotify(channel, payload))
// return;
and launched this version of pg into production.
This was the only way I could figure out if there was a significant difference in speed. And the results turned out to be very interesting, the query speed increased by about two times. But unfortunately it's still far from the desired level
before the code changes
rmdatabase=# select pg_notify('rmdb_client_message','{"Command":239,"MsgId":"48117898"}');
Время: 974,119 мс
rmdatabase=# select pg_notify('rmdb_client_message','{"Command":239,"MsgId":"48117898"}');
Время: 859,855 мс
rmdatabase=# select pg_notify('rmdb_client_message','{"Command":239,"MsgId":"48117898"}');
Время: 695,741 мс
rmdatabase=# select pg_notify('rmdb_client_message','{"Command":239,"MsgId":"48117898"}');
Время: 77,001 мс
rmdatabase=# select pg_notify('rmdb_client_message','{"Command":239,"MsgId":"48117898"}');
Время: 475,590 мс
rmdatabase=# select pg_notify('rmdb_client_message','{"Command":239,"MsgId":"48117898"}');
Время: 973,449 мс
rmdatabase=# select pg_notify('rmdb_client_message','{"Command":239,"MsgId":"48117898"}');
Время: 1039,825 мс (00:01,040)
rmdatabase=# select pg_notify('rmdb_client_message','{"Command":239,"MsgId":"48117898"}');
Время: 1233,576 мс (00:01,234)
after the code changes
rmdatabase=# select pg_notify('rmdb_client_message','{"Command":239,"MsgId":"48119697"}');
Время: 431,337 мс
rmdatabase=# select pg_notify('rmdb_client_message','{"Command":239,"MsgId":"48119697"}');
Время: 460,794 мс
rmdatabase=# select pg_notify('rmdb_client_message','{"Command":239,"MsgId":"48119697"}');
Время: 498,042 мс
rmdatabase=# select pg_notify('rmdb_client_message','{"Command":239,"MsgId":"48119697"}');
Время: 604,931 мс
rmdatabase=# select pg_notify('rmdb_client_message','{"Command":239,"MsgId":"48119697"}');
Время: 438,763 мс
rmdatabase=# select pg_notify('rmdb_client_message','{"Command":239,"MsgId":"48119697"}');
Время: 587,827 мс
rmdatabase=# select pg_notify('rmdb_client_message','{"Command":239,"MsgId":"48119697"}');
Время: 621,079 мс
rmdatabase=# select pg_notify('rmdb_client_message','{"Command":239,"MsgId":"48119697"}');
Время: 549,264 мс
rmdatabase=# select pg_notify('rmdb_client_message','{"Command":239,"MsgId":"48119697"}');
Время: 447,218 мс
rmdatabase=# select pg_notify('rmdb_client_message','{"Command":239,"MsgId":"48119697"}');
Время: 526,980 мс
rmdatabase=# select pg_notify('rmdb_client_message','{"Command":239,"MsgId":"48119697"}');
Время: 417,556 мс
rmdatabase=# select pg_notify('rmdb_client_message','{"Command":239,"MsgId":"48117898"}');
Время: 185,374 мс
rmdatabase=# select pg_notify('rmdb_client_message','{"Command":239,"MsgId":"48117898"}');
Время: 554,529 мс
rmdatabase=# select pg_notify('rmdb_client_message','{"Command":239,"MsgId":"48117898"}');
Время: 654,769 мс
rmdatabase=# select pg_notify('rmdb_client_message','{"Command":239,"MsgId":"48117898"}');
Время: 577,187 мс
rmdatabase=# select pg_notify('rmdb_client_message','{"Command":239,"MsgId":"48117898"}');
Время: 246,831 мс
rmdatabase=# select pg_notify('rmdb_client_message','{"Command":239,"MsgId":"48117898"}');
Время: 648,865 мс
tomorrow I will deal with the perf
--
Arsen Arutyunyan
Arsen Arutyunyan
Вторник, 15 марта 2022, 17:32 +03:00 от Tom Lane <tgl@sss.pgh.pa.us>:
Арсен Арутюнян <arutar@bk.ru> writes:
> i looked at the file "\src\backend\commands\async.c"
> there is a check for duplicate messages
Yup.
> Is this slowdown related to this check?
[ shrug... ] You've provided no evidence either for or against that
possibility.
It seems a little unlikely that you could have a lot of pending messages
without also seeing data accumulating in pg_notify/, but on the other hand
it's also hard to think of other places that time could be getting spent
if the queue is always empty. Can you use perf(1) or some such tool to
try to identify where the time is being spent? There's some advice
about that here:
https://wiki.postgresql.org/wiki/Profiling_with_perf
> Is it possible to skip the check if I'm absolutely sure the message is unique?
Not a good idea. You could upgrade to PG 13 or later, where that
code has been improved.
regards, tom lane
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