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Date: Fri, 15 Feb 2008 18:36:06 -0600
From: Eric Sandeen <sandeen@sandeen.net>
MIME-Version: 1.0
Subject: Re: rewrite very slow
References: <20080215191636.GC4859@bob.dscon.sk>
In-Reply-To: <20080215191636.GC4859@bob.dscon.sk>
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To: DS <xfs@bob.dscon.sk>
Cc: xfs@oss.sgi.com

DS wrote:
> Hello,
> 
> I need some help to tunning my storage.

...
> TIME 43 sekund


What kernel?  when I test on my 2.6.23.9-85.fc8 and 2.6.22.5 boxes, I
see 2 and 7 seconds for rewrite, respectively.

but granted, on ext3 I get 0 seconds for every run.

Also the difference appears to be O_TRUNC (which the perl script does);
if I code it in c:

#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>

void main(void)
{
        int i;
        int fd;
        char file[4];

        for (i = 0; i < 100; i++) {
                sprintf(file, "%d.txt", i);
                fd = open(file, O_CREAT|O_RDWR|O_TRUNC, 0644);
                write(fd, "aaaaaaaaaaaaaaaaaaa\n");
                close(fd);
        }
}

rewrite is a bit slower w/ O_TRUNC in place, plenty fast w/o it.  Not
sure about the xfs/ext3 difference... this is probably a side-effect of
flushes xfs put into place on truncate (IIRC?)

-Eric