From: | Peter Geoghegan <pg(at)heroku(dot)com> |
---|---|
To: | Josh Berkus <josh(at)agliodbs(dot)com> |
Cc: | Jeff Janes <jeff(dot)janes(at)gmail(dot)com>, Stephen Frost <sfrost(at)snowman(dot)net>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Andrew Dunstan <andrew(at)dunslane(dot)net>, Robert Haas <robertmhaas(at)gmail(dot)com>, Gavin Flower <GavinFlower(at)archidevsys(dot)co(dot)nz>, KONDO Mitsumasa <kondo(dot)mitsumasa(at)lab(dot)ntt(dot)co(dot)jp>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: Add min and max execute statement time in pg_stat_statement |
Date: | 2013-10-24 00:17:23 |
Message-ID: | CAM3SWZT9SqdfF7h5xHB9bOKft1hTj3Tfu8=dKL-uzoX0L9s=dw@mail.gmail.com |
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On Wed, Oct 23, 2013 at 4:51 PM, Peter Geoghegan <pg(at)heroku(dot)com> wrote:
> No, I'm not. I'm suggesting storing the query texts externally, in a
> file. They usually use 1024 bytes of shared memory per entry,
> regardless of how long the query text is.
I should add that I think that that's about the useful limit of such
schemes. Maybe we could buy a bit more breathing room by storing some
of the stats externally, but I doubt it'd be worth it. I'm not
interested in optimizing pg_stat_statements in the direction of
supporting aggregating a number of distinct entries past much more
than 10,000. I am interested in making it store richer statistics,
provided we're very careful about the costs. Every time those counters
are incremented, a spinlock is held. I don't want everyone to have to
pay any non-trivial additional cost for that, given that the added
instrumentation may not actually be that useful to most users who just
want a rough picture.
--
Peter Geoghegan
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