fsync() takes about 0.06 second ---makes Cyrus deliver slow

[David Lang]

the thing is that the fsync has more of an effect then the raw numbers
would indicate. while one process is doing an fsync the other processes
are waiting for the fsync to finish so that they can write to the disk.

David Lang


On Tue, 10 Sep 2002, Su Li wrote:

> Date: Tue, 10 Sep 2002 10:31:05 -0400
> From: Su Li <sli at rim.net>
> To: "'rscuss at omniti.com'" <rscuss at omniti.com>, Su Li <sli at rim.net>,
>      "'dlang at diginsite.com'" <dlang at diginsite.com>
> Cc: 'Jure Pecar' <pegasus at telemach.net>, info-cyrus at lists.andrew.cmu.edu
> Subject: RE: fsync() takes about 0.06 second ---makes Cyrus deliver slow
>
> Daniel,
>
> My Linux is red hat 7.2-1 with kernel 2.4.7-10. The file system is ext3.
> Hard disk it RAID5.
>
> Jure,
> Thanks for your configuration. I 'll give a try and post my result to the
> new group.
>
> David,
> I tried remove suppression from /etc/cyrus.conf. The suppression is still
> there. Maybe I should try remove it from the code.
>
>
> -----
> Besides, I did some calculation on the time of the system calls on a
> new-email. 3 fcync takes about 0.15 seconds. Each mail overall takes 0.65
> seconds. I see the number of locks and deliver process can go up to
> thousands. Maybe some thing else is also taking big time, say the
> communication between deliver and lmtpd?
>
> Anyway, I'll keep trying. Thanks for every body's help. If anybody got some
> idea, please let me know.
>
>
> Su
>
>
>
>
> -----Original Message-----
> From: Robert Scussel [mailto:rscuss at omniti.com]
> Sent: September 9, 2002 4:58 PM
> To: Su Li
> Cc: 'Jure Pecar'; info-cyrus at lists.andrew.cmu.edu
> Subject: Re: fsync() takes about 0.06 second ---makes Cyrus deliver slow
>
>
> Depending on how consistent you want your data, you can always define
> your own fsync which can do nothing and then call sync directly from
> somewhere else. This is however dangerous, as you could experience file
> corruption.
>
> Out of curiousity, what fs/OS are you using? We have noted this as a
> major factor of fsync times.
>
> B
>
> Su Li wrote:
> > Thanks Jure,
> >
> > I asked my system adm. He said I could change the hard disk to RAID1+0
> which
> > can problely give me 2 time faster. And I have put /spool/imap/user in a
> > seprate disk already. Even if times 2, I can only get 2-3 emails per
> second.
> > I have 15,000 users on the server. That is still slow.
> >
> >
> >
> > Su
> >
> > -----Original Message-----
> > From: Jure Pecar [mailto:pegasus at telemach.net]
> > Sent: September 9, 2002 4:27 PM
> > To: Su Li
> > Cc: info-cyrus at lists.andrew.cmu.edu
> > Subject: Re: fsync() takes about 0.06 second ---makes Cyrus deliver slow
> >
> >
> > On Mon, 9 Sep 2002 16:00:28 -0400
> > Su Li <sli at rim.net> wrote:
> >
> >
> >>I wonder is there any way to may fsync() faster? If not is there any way
> >>to call fsync less often? Will using a fast hard disk help? Or will move
> >>the mail store -- /spool/imap/user to a database help?
> >
> >
> > For what i know, fsync() speed is directly poportional to the speed of
> your
> > disks (avg. access time more than r/w speed). The most you can do is to
> keep
> > different cyrus files on differet physical disks, possibly on differnet
> raid
> > arrays. Remember, mail means lots of fsync()s means disk being the
> > bottleneck. If you really need the performance, check some of the solid
> > state disks available around the net.
> >
> >
> > --
> >
> >
> > Jure Pecar
> >
>
>
>
> --
> Robert Scussel
> 1024D/BAF70959/0036 B19E 86CE 181D 0912  5FCC 92D8 1EA1 BAF7 0959
>