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Re: [HACKERS] fsync method checking

From: Kurt Roeckx <Q(at)ping(dot)be>
To: Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us>
Cc: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>,Mark Kirkwood <markir(at)paradise(dot)net(dot)nz>,pgsql-performance(at)postgresql(dot)org,PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: [HACKERS] fsync method checking
Date: 2004-03-18 20:26:21
Message-ID: 20040318202621.GB8330@ping.be (view raw or flat)
Thread:
Lists: pgsql-hackerspgsql-performance
Here are my results on Linux 2.6.1 using cvs version 1.7.

Those times with > 20 seconds, you really hear the disk go crazy.

And I have the feeling something must be wrong.  Those results
are reproducible.


Kurt


Simple write timing:
        write                    0.139558

Compare fsync times on write() and non-write() descriptor:
(If the times are similar, fsync() can sync data written
 on a different descriptor.)
        write, fsync, close      8.249364
        write, close, fsync      8.356813

Compare one o_sync write to two:
        one 16k o_sync write    28.487650
        two 8k o_sync writes     2.310304

Compare file sync methods with one 8k write:
        (o_dsync unavailable)
        open o_sync, write       1.010688
        write, fdatasync        25.109604
        write, fsync,           26.051218

Compare file sync methods with 2 8k writes:
(The fastest should be used for wal_sync_method)
        (o_dsync unavailable)
        open o_sync, write       2.212223
        write, fdatasync        27.439907
        write, fsync,           27.772294


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