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Re: ext3 and indexed directories

On Mar 06, 2003  10:20 -0500, Huntress Gary B NPRI wrote:
> I work with a MySQL installation containing several thousand databases.
> MySQL represents each database as a seperate sub-directory of the main
> MySQL data directory.  As the number of databases increases it seems
> that the time to connect is increasing significantly and I believe this
> is probably due to the time necessary to search through the large number
> of directory entries.

Yes, you will see this as a significant increase in system time for
directory access.  The stock ext2/3 directory code doesn't work so well
past about 5000 entries in a single directory (it survives up to about
10000 entries, but basically dies after that.

We have been testing older indexed directory code (also called htree)
with directory sizes up to 10M files.  With a fast RAID back-end, we
are getting creation rates up to 30000-40000/s.

> It has been suggested to me to look into the "indexed directory"
> patch for ext3 in order to increase performance.  Can anyone give me an
> idea how stable this is?  Is it suitable for a production environment?
> If yes, a pointer to the patch would be very helpful.

If you would have asked that question a week or two ago, you would have
recieved a resounding "unstable" in reply.  However, there were a couple
of major bugs fixed recently, and after that things are apparently working
very well.  I'd suggest looking at the archives of ext3-users and/or
ext2-devel for details of problems and patches.  I'm not sure whether Ted
has been keeping his 2.4 htree patches up-to-date with the latest fixes
and kernels or not.

Cheers, Andreas
Andreas Dilger

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