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Re: Free WAL caches on switching segments

From: Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us>
To: ITAGAKI Takahiro <itagaki(dot)takahiro(at)lab(dot)ntt(dot)co(dot)jp>
Cc: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, pgsql-patches(at)postgresql(dot)org
Subject: Re: Free WAL caches on switching segments
Date: 2005-09-23 17:56:09
Message-ID: 200509231756.j8NHu9U13411@candle.pha.pa.us (view raw or flat)
Thread:
Lists: pgsql-patches
ITAGAKI Takahiro wrote:
> Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> 
> > > Here is a small patch to prevent undesired WAL file caching by kernel.
> > > posix_fadvise(POSIX_FADV_DONTNEED) attempts to free cached pages and
> > > the kernel will discard them in preference to other data caches.
> > 
> > On plenty of platforms, this won't even compile ...
> 
> 
> Do you mean simply following code? or more pretty way?
> 
> #ifdef POSIX_FADV_DONTNEED
> 	posix_fadvise(openLogFile, 0, 0, POSIX_FADV_DONTNEED);
> #endif

Yes, but we probably have to have a configure test to see if
posix_fadvise exists too.  I will keep this for 8.2.

-- 
  Bruce Momjian                        |  http://candle.pha.pa.us
  pgman(at)candle(dot)pha(dot)pa(dot)us               |  (610) 359-1001
  +  If your life is a hard drive,     |  13 Roberts Road
  +  Christ can be your backup.        |  Newtown Square, Pennsylvania 19073

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