Re: ext3 throughput woes on certain (possibly heavily fragmented) files

[jw schultz]

On Mon, Sep 16, 2002 at 03:39:11PM -0700, Simon Kirby wrote:
> This box is primarily running a POP3 server (written in-house to cache
> mbox offsets, so that it can handle a huge volume of mail), and also
> exports the mail spool via NFS to other servers which run exim (-fsync). 
> nfsd is exported async.  Everything is mounted noatime, nodiratime.  No
> applications should be calling sync/fsync/fdatasync or using O_SYNC. 
> It's a mail server, so everything is fragmented.
> 
> We're using dotlocking.  Would this cause metadata journalling?  We had
> to hash the mail spool a long time ago do to system time eating all CPU
> (the ext2 linear directory scan to find a slot available in the spool
> directory to add the dotlock file).  I estimate about 200 - 300 dotlock
> files are created per second, but these should all be asynchronous. 
> Would switching to fctnl() locking (if this works over NFS) solve the
> problem?

I'd absolutly go to fcntl().  As bad as dotlocking is for
journaling filesystems it is even worse for NFS (when it works).
Look at the lkml thread "invalidate_inode_pages in 2.5.32/3"
to get an idea.  Multiply the directory invalidations by the
size of the directories.  fcntl() is the preferred way of locking
over NFS as it will even report if there is a problem with
lockd.

-- 
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	J.W. Schultz            Pegasystems Technologies
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