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Re: [HACKERS] fsync method checking

From: Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us>
To: Kurt Roeckx <Q(at)ping(dot)be>
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 20:34:21
Message-ID: 200403182034.i2IKYLp27844@candle.pha.pa.us (view raw or flat)
Thread:
Lists: pgsql-hackerspgsql-performance
Kurt Roeckx wrote:
> 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.
> 

Wow, your O_SYNC times are great.  Where can I buy some?  :-)

Anyway, we do need to find a way to test this because obviously there is
huge platform variability.

---------------------------------------------------------------------------


> 
> 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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-- 
  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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