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From "Julian Dunn" <Julian_D...@cbc.ca>
Subject [users@httpd] BerkeleyDB RewriteMap on NFS - problems?
Date Tue, 19 Dec 2006 05:33:03 GMT
Hi all,

Recently we implemented the use of a BerkeleyDB-based RewriteMap under
Apache 1.3.x for our production environment of 6 webservers. The .db and
.pag files resided on an NFS share served by a commercial NAS device and
were only read by the webservers, not written; updates to the BDB were
done on a separate utility machine.

We experienced a lot of problems with this setup; after an
indeterminate period of time, the httpd processes would become
unresponsive and appear in the "nfs_wait" state while the system load
skyrocketed (probably as a result of the NFS shares being mounted
"soft"). After changing all servers' NFS options to "hard" we were able
to kill the unresponsive httpd's but Apache would fail to restart unless
the machine was rebooted. (An strace indicated the the machine was
getting stuck on a stat64() of the .pag file.)

I have a couple of questions for the list:

1) Is it bad to put BDB RewriteMaps on an NFS server? Is anyone else
doing it without problems?
2) Is it true that some versions of BerkeleyDB don't have "read-only"
semantics, and could this be causing the problem?
3) Is the problem here related to incorrect POSIX file-locking
semantics on the NFS server as some of my colleagues at work have
implied? This NFS server hardware is fairly recent (purchased within the
last 3 years) so I'd be very surprised if this were the case.
4) Could it be possible that this is just tickling a bug in the Linux
kernel? We're running SuSE Linux Enterprise Server 9.

Any thoughts or insights would be welcome.

- Julian

--
-- Julian C. Dunn, P.Eng.  <Julian_Dunn@cbc.ca>
-- Platform Administrator * CBC.ca Production & Operations
-- Office: 2C310-J  *  Tel.: (416) 205-3311 x6988

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