improving concurrency/performance (fwd)

Andrew McNamara andrewm at
Wed Nov 9 21:45:40 EST 2005

>>> This guy is having a problem with cyrus-imap and ext3 - when multiple
>>> processes are attempting to write to the one filesystem (but not the one
>>> file), performance drops to next to nothing when only five processes are
>>> writing. An strace shows most of the time is being spent in fdatasync
>>> and fsync.
>Actually, the thread just got off topic quickly -- I'm running this on
>reiserfs, not ext3.  ...And I've got it mounted with data=writeback, too.
>But thanks for the info, Andrew.

Sorry, my confusion. But it might be worth asking the reiserfs guys.

My experience has been that if you are fsync'ing files, then even modern
disks only get around 10 fsync's per second (because not only does the
file data get writen out, but typically the inode, the directory entry,
the free block table and maybe even all the directory entries up to root).

Journalling can help, because the commited data is writen sequentially
to the journal, rather than being scattered all over the disk, but the
journalled operations still need to be applied to the filesystem sooner
or later.

Andrew McNamara, Senior Developer, Object Craft

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