Re: Postgres performance comments from a MySQL user
От | Arjen van der Meijden |
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Тема | Re: Postgres performance comments from a MySQL user |
Дата | |
Msg-id | 005a01c3343e$380193b0$3ac15e91@acm обсуждение исходный текст |
Ответ на | Re: Postgres performance comments from a MySQL user ("scott.marlowe" <scott.marlowe@ihs.com>) |
Ответы |
Re: Postgres performance comments from a MySQL user
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Список | pgsql-general |
> -----Oorspronkelijk bericht----- > Van: pgsql-general-owner@postgresql.org > [mailto:pgsql-general-owner@postgresql.org] Namens scott.marlowe > Verzonden: maandag 16 juni 2003 21:00 > Aan: Ernest E Vogelsinger > CC: Justin Clift; Joseph Shraibman; pgsql-general@postgresql.org > Onderwerp: Re: [GENERAL] Postgres performance comments from a > MySQL user > > I have a query that runs for 17secs for the first time. Now, when > > executed a second time, it consumes 270 msec. From the > third execution > > it's running with 29 msec. > > > > However this only holds for the open connection. When > connecting anew, > > it starts with 270 msec and drops to 29 msec again. > > > > Any clues about this interesting behaviour? > > So, once the machine's been up a while, the 17 second > behaviour goes away > completely, but the .27 second -> .03 second behaviour remains? > > Hmmmm. Sounds like the very first time you run it the data > set moves from > disk to kernel cache. Then on each new connect postgresql > pulls it from > kernel cache to postgresql's buffer, and it's faster still. Recent postgresql versions (7.3.3 perhaps? Dunno when it got included) cache the query-plans on the connection that was used for that connection. So postgres won't have to replan the entire query and that allows a speedup, although the difference in time is quite large, perhaps there is more cacheing with the connection than just the queryplan. Regards, Arjen
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