| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Andres Freund <andres(at)anarazel(dot)de> |
| Cc: | Jeff Davis <pgsql(at)j-davis(dot)com>, Corey Huinker <corey(dot)huinker(at)gmail(dot)com>, Michael Paquier <michael(at)paquier(dot)xyz>, jian he <jian(dot)universality(at)gmail(dot)com>, Nathan Bossart <nathandbossart(at)gmail(dot)com>, Bruce Momjian <bruce(at)momjian(dot)us>, Matthias van de Meent <boekewurm+postgres(at)gmail(dot)com>, Magnus Hagander <magnus(at)hagander(dot)net>, Stephen Frost <sfrost(at)snowman(dot)net>, Ashutosh Bapat <ashutosh(dot)bapat(dot)oss(at)gmail(dot)com>, Peter Smith <smithpb2250(at)gmail(dot)com>, PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org>, alvherre(at)alvh(dot)no-ip(dot)org |
| Subject: | Re: Statistics Import and Export |
| Date: | 2025-02-21 20:49:10 |
| Message-ID: | 3663519.1740170950@sss.pgh.pa.us |
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| Lists: | pgsql-hackers |
Andres Freund <andres(at)anarazel(dot)de> writes:
> Which to me rather strongly suggests pg_dump has gotten a *lot* slower with
> this change.
Well, it's doing strictly more work, so somewhat slower is to be
expected. But yeah, more than 2x slower is not nice.
In a quick look at the committed patch, it doesn't seem to have
used any of the speedup strategies we applied to pg_dump a couple
of years ago. One or the other of these should help:
* Issue a single query to fetch stats from every table we're dumping
* Set up a prepared query to avoid re-planning the per-table query
(compare be85727a3)
I'm not sure how workable the first of these would be though.
It's not hard to imagine it blowing out pg_dump's memory usage
for a DB with a lot of tables and high default_statistics_target.
The second one should be relatively downside-free.
regards, tom lane
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