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Re: ice-broker scan thread

From: David Boreham <david_list(at)boreham(dot)org>
To: pgsql-hackers(at)postgresql(dot)org
Subject: Re: ice-broker scan thread
Date: 2005-11-30 14:33:18
Message-ID: 438DB82E.7060507@boreham.org (view raw or flat)
Thread:
Lists: pgsql-hackers
>Yes. The O_DIRECT issue is my biggest concern about Linux at the moment.
>That being said, the plan is to only pre-fetch the next N blocks, where N
>< 32, and to read them into the local buffer cache. In a situation where
>space in the cache low (and prefetched pages might be pushed out before we
>even get to read them), we need to provide such information to the
>readahead mechanism so that it can reduce the number of blocks which it
>prefetches.
>
>
>  
>
Would you open a separate handle O_DIRECT, just for the prefetch ?

My experience with O_DIRECT and databases in the past has not been
great : what you gain with being able to control your own caching you loose
(and more) in other ways.

BTW, has anyone tried O_DIRECT and the prefetch idea on Linux ?
I'm wondering if it may not work (because the read data won't get cached
in the fs cache due to O_DIRECT).




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