[Dovecot] index performance issues

[Timo Sirainen]

On Tue, 2007-03-13 at 00:58 +0000, John Lyons wrote:
> 
> If we were in a position to see 'an index or three' as being the
> cause, we'd
> have been happy to fix those but we're seeing 20+ pop logins and 90%
> of them
> dead. Kill the processes and 60 seconds later there's another 20 dead
> processes and the pop server has a load of 20+ and NFS traffic is
> 100Mbit. 

If this happens again, it would help fixing the problem if you:

1. Strace some of the hanging processes. What is it doing? If there are
multiple processes for the same user, I suppose most of them are waiting
for a lock. If it's not a locking problem, then:

2. Copy some of the hanging users' mailboxes and their indexes to some
temporary location. Once everything is working again, try if it logging
into those saved broken mailboxes still hangs. If they do, I'd like to
get the dovecot.index, dovecot.index.log and dovecot-uidlist files and a
list of files in the maildir. Those are probably enough to reproduce the
bug and they don't contain any actual mail contents.

Although if the hang depends on a broken dovecot.index.cache file as
well, it can get more problematic since that file might contain some
message headers. But with POP3-only users it should contain only message
sizes and no headers.
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