| From: | Bruce Momjian <bruce(at)momjian(dot)us> |
|---|---|
| To: | Julien Rouhaud <rjuju123(at)gmail(dot)com> |
| Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Robert Haas <robertmhaas(at)gmail(dot)com>, Michael Paquier <michael(at)paquier(dot)xyz>, Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org>, torikoshia <torikoshia(at)oss(dot)nttdata(dot)com>, Atsushi Torikoshi <atorik(at)gmail(dot)com>, Tatsuro Yamada <tatsuro(dot)yamada(dot)tf(at)nttcom(dot)co(dot)jp>, Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com>, Evgeny Efimkin <efimkin(at)yandex-team(dot)ru>, PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org> |
| Subject: | Re: Feature improvement: can we add queryId for pg_catalog.pg_stat_activity view? |
| Date: | 2020-10-16 15:04:49 |
| Message-ID: | 20201016150449.GA23488@momjian.us |
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| Lists: | pgsql-hackers |
On Thu, Oct 15, 2020 at 11:41:23AM +0800, Julien Rouhaud wrote:
> On Wed, Oct 14, 2020 at 10:40 PM Bruce Momjian <bruce(at)momjian(dot)us> wrote:
> > There is that, and log_line_prefix, which I can imaging being useful.
> > My point is that if the queryid is visible, there should be a reason it
> > defaults to show empty.
>
> I did some naive benchmarking. Using a custom pgbench script with this query:
>
> SELECT *
> FROM pg_class c
> JOIN pg_attribute a ON a.attrelid = c.oid
> ORDER BY 1 DESC
> LIMIT 1;
>
> I can see around 2% overhead (this query is reported with ~ 3ms
> latency average). Adding a few joins, overhead goes down to 1%.
That number is too high to enable this by default. I suggest we either
improve the performance of this, or clearly document that you have to
enable the hash computation to see the pg_stat_activity and
log_line_prefix fields.
--
Bruce Momjian <bruce(at)momjian(dot)us> https://momjian.us
EnterpriseDB https://enterprisedb.com
The usefulness of a cup is in its emptiness, Bruce Lee
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