| From: | Peter Geoghegan <pg(at)heroku(dot)com> |
|---|---|
| To: | Stephen Frost <sfrost(at)snowman(dot)net> |
| Cc: | Jeff Janes <jeff(dot)janes(at)gmail(dot)com>, Gavin Flower <GavinFlower(at)archidevsys(dot)co(dot)nz>, Marc Mamin <M(dot)Mamin(at)intershop(dot)de>, KONDO Mitsumasa <kondo(dot)mitsumasa(at)lab(dot)ntt(dot)co(dot)jp>, Dimitri Fontaine <dimitri(at)2ndquadrant(dot)fr>, 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>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Add min and max execute statement time in pg_stat_statement |
| Date: | 2013-10-23 23:48:22 |
| Message-ID: | CAM3SWZT7XCZ9SXSiW+tJvHi+SF1sygp2m1fRKnyuJFgdr0by7g@mail.gmail.com |
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On Wed, Oct 23, 2013 at 4:34 PM, Stephen Frost <sfrost(at)snowman(dot)net> wrote:
> Any chance we could accumulate into the histogram in local memory and
> only push to the shared memory on an "infrequent" or at least "less
> frequent" basis? Apologies, I've not looked into the pg_stat_statements
> bits all that closely, but I can certainly see how having to hold it all
> in shared memory with locking to update would be painful..
I doubt it. That trick I proposed around storing the query text in an
external file is only feasible because we never update the query text,
and we hardly ever care what it actually is in practice. Contrast that
with something that is in a structure protected by a spinlock. You'd
have to keep deltas stashed in TopMemoryContext, and for all kinds of
common cases that just wouldn't work. Plus you have to have some whole
new mechanism for aggregating the stats across backends when someone
expresses an interest in seeing totals.
--
Peter Geoghegan
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