Discarding the resulting rows
in [PgSql]
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From: "Kevin Grittner" on 26 Apr 2010 15:36 "Murali M. Krishna" <murali1729(a)yahoo.com> wrote: > Basically, I would like to discard the result rows after doing all > the work required to execute the query. I would use EXPLAIN ANALYZE SELECT ... > I looked at the documentation and I saw something about using the > keyword PERFORM rather than SELECT. I don't remember ever seeing anything like that. Do you have a URL? > How do I clear the buffer caches between two query runs? The easiest way to clear the PostgreSQL cache is to restart the service. PostgreSQL goes through the OS cache; so you'll need to clear that, too. How you do that is dependent on your OS. Of course, in most real use cases, a significant portion of the database would be cached, so unless you're dealing with a very unusual situation, it's hard to see what the value would be of such a benchmark, unless you're trying to create an artificial "worst case" scenario for bounding purposes. Oh, and most serious database servers have 256MB or more of battery backed cache on the RAID controller; don't forget to deal with that somehow. -Kevin -- Sent via pgsql-hackers mailing list (pgsql-hackers(a)postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
From: Jaime Casanova on 26 Apr 2010 15:49 On Mon, Apr 26, 2010 at 2:36 PM, Kevin Grittner <Kevin.Grittner(a)wicourts.gov> wrote: > "Murali M. Krishna" <murali1729(a)yahoo.com> wrote: > >> I looked at the documentation and I saw something about using the >> keyword PERFORM rather than SELECT. > > I don't remember ever seeing anything like that.  Do you have a URL? > i guess he is refering to the plpgsql's PERFORM statement, which of course he can't use outside a plpgsql function... mmm... well, IIRC, in 9.0 he will be able to do DO $$ PERFORM * FROM tabla; $$ LANGUAGE plpgsql; but i think DO is not an EXPLAINing statement -- Atentamente, Jaime Casanova Soporte y capacitación de PostgreSQL AsesorÃa y desarrollo de sistemas Guayaquil - Ecuador Cel. +59387171157 -- Sent via pgsql-hackers mailing list (pgsql-hackers(a)postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
From: Robert Haas on 26 Apr 2010 16:03 On Mon, Apr 26, 2010 at 3:36 PM, Kevin Grittner <Kevin.Grittner(a)wicourts.gov> wrote: > "Murali M. Krishna" <murali1729(a)yahoo.com> wrote: > >> Basically, I would like to discard the result rows after doing all >> the work required to execute the query. > > I would use EXPLAIN ANALYZE SELECT ... There's some overhead to that, of course. .....Robert -- Sent via pgsql-hackers mailing list (pgsql-hackers(a)postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
From: Jaime Casanova on 26 Apr 2010 16:16 On Mon, Apr 26, 2010 at 3:03 PM, Robert Haas <robertmhaas(a)gmail.com> wrote: > On Mon, Apr 26, 2010 at 3:36 PM, Kevin Grittner > <Kevin.Grittner(a)wicourts.gov> wrote: >> "Murali M. Krishna" <murali1729(a)yahoo.com> wrote: >> >>> Basically, I would like to discard the result rows after doing all >>> the work required to execute the query. >> >> I would use EXPLAIN ANALYZE SELECT ... > > There's some overhead to that, of course. > he could see the "actual time" in the very first row of the EXPLAIN ANALYZE... isn't that a value that is more close to what the OP is looking for? -- Atentamente, Jaime Casanova Soporte y capacitación de PostgreSQL AsesorÃa y desarrollo de sistemas Guayaquil - Ecuador Cel. +59387171157 -- Sent via pgsql-hackers mailing list (pgsql-hackers(a)postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
From: "Kevin Grittner" on 26 Apr 2010 16:24 Robert Haas <robertmhaas(a)gmail.com> wrote: > On Mon, Apr 26, 2010 at 3:36 PM, Kevin Grittner > <Kevin.Grittner(a)wicourts.gov> wrote: >> "Murali M. Krishna" <murali1729(a)yahoo.com> wrote: >> >>> Basically, I would like to discard the result rows after doing >>> all the work required to execute the query. >> >> I would use EXPLAIN ANALYZE SELECT ... > > There's some overhead to that, of course. Good point. At the moment I can't think how to do better, though. Other suggestions, anyone? -Kevin -- Sent via pgsql-hackers mailing list (pgsql-hackers(a)postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
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