[PERFORM] preloading indexes
I am working with some pretty convoluted queries that work very slowly the first time they’re called but perform fine on the second call. I am fairly certain that these differences are due to the caching. Can someone point me in a direction that would allow me to pre-cache the critical indexes?
Re: [PERFORM] preloading indexes
Title: Message That’s correct – I’d like to be able to keep particular indexes in RAM available all the time The best way to get all the stuff needed by a query into RAM is to run the query. Is it more that you want to 'pin' the data in RAM so it doesn't get overwritten by other queries? I am working with some pretty convoluted queries that work very slowly the first time they’re called but perform fine on the second call. I am fairly certain that these differences are due to the caching. Can someone point me in a direction that would allow me to pre-cache the critical indexes?
Re: [PERFORM] preloading indexes
The caching appears to disappear overnight. The environment is not in production yet so I'm the only one on it. Is there a time limit on the length of time in cache? I believe there is sufficient RAM, but maybe I need to look again. s -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Andrew Sullivan Sent: Wednesday, November 03, 2004 12:35 PM To: [EMAIL PROTECTED] Subject: Re: [PERFORM] preloading indexes On Wed, Nov 03, 2004 at 12:12:43PM -0700, [EMAIL PROTECTED] wrote: > That's correct - I'd like to be able to keep particular indexes in RAM > available all the time If these are queries that run frequently, then the relevant cache will probably remain populated[1]. If they _don't_ run frequently, why do you want to force the memory to be used to optimise something that is uncommon? But in any case, there's no mechanism to do this. A [1] there are in fact limits on the caching: if your data set is larger than memory, for instance, there's no way it will all stay cached. Also, VACUUM does nasty things to the cache. It is hoped that nastiness is fixed in 8.0. -- Andrew Sullivan | [EMAIL PROTECTED] The plural of anecdote is not data. --Roger Brinner ---(end of broadcast)--- TIP 8: explain analyze is your friend ---(end of broadcast)--- TIP 5: Have you checked our extensive FAQ? http://www.postgresql.org/docs/faqs/FAQ.html
Re: [PERFORM] preloading indexes
Thanks - this is what I was afraid of, but I may have to do this Is there a good way to monitor what's in the cache? j <[EMAIL PROTECTED]> writes: > The caching appears to disappear overnight. You've probably got cron jobs that run late at night and blow out your kernel disk cache by accessing a whole lot of non-Postgres stuff. (A nightly disk backup is one obvious candidate.) The most likely solution is to run some cron job a little later to exercise your database and thereby repopulate the cache with Postgres files before you get to work ;-) regards, tom lane ---(end of broadcast)--- TIP 2: you can get off all lists at once with the unregister command (send "unregister YourEmailAddressHere" to [EMAIL PROTECTED])
