RE: OpenLDAP, bdb and Linux filesystems

["Howard Chu" <hyc@highlandsun.com>]

> -----Original Message-----
> From: owner-openldap-software@OpenLDAP.org
> [mailto:owner-openldap-software@OpenLDAP.org]On Behalf Of Stephan Siano

> has anyone here done performance measurements with OpenLDAP and the
> bdb-backend on differen Linux filesystems (the filesystem
> where the database is stored)?

I've only used ext2fs.

> The background of the question is that we encountered performance
> problems with subversion (which also stores the data in a berkeley-db)
> when the database was stored on an ext3-FS. On closer examination we
> found out, that for a simple testcase (Import of a 40MB repository) ext3
> was about four times slower than ext2 (and reiserfs wasn't too much
> better than ext3, while xfs wasn't too much slower than ext2). It seems
> to me, that berkeley-db and ext3 (and reiser) filesystems don't play
> together too well.

What are the relative speeds of each filesystem when doing a plain write()
with 40MB of data?

> Has anybody observed a similar behaviour for OpenLDAP? Is only the
> slapadd command affected or can a siginificant slowdown also be observed
> in normal directory operation?

Was the BDB database configured correctly? At the very least, did you
configure the database to store the BDB logs on a separate spindle from the
BDB data?

What kind of hardware was used for this test, what kind of disk controllers?
Since reiser and ext3 are journaling filesystems, I would expect a much
larger I/O demand than for ext2. Coupled with the write-ahead logging that
BDB does itself, this would lead to 2-4x the I/O load of an ext2fs
installation if it's all writing to a single filesystem. Perhaps the I/O
subsystem of the machine cannot support the demand. Even with multiple disks,
without SCSI or connect/disconnect and command queuing it would be asking an
awful lot of a typical Intel-based machine.

  -- Howard Chu
  Chief Architect, Symas Corp.       Director, Highland Sun
  http://www.symas.com               http://highlandsun.com/hyc
  Symas: Premier OpenSource Development and Support