[Dovecot] index performance issues

[John Lyons]

> Thats not what you said - you said the disk *filled up*, after which you
> chose to delete *all* of the indexes, causing *all* of them to have to
> be rebuilt. This (deleting *all* indexes) is very different from just
> isolated, occasional corruption of an index or three, causing just
> *those* indexes to have to be rebuilt (trivial).

In the last 8 weeks we've ended up in a situation where 4 times we've seen
no alternative but to delete the indexes and start from scratch.
First was a version upgrade which pushed the NFS server to 100% network
usage and caused all of the pop downloads to die. It looked like dovecot was
rebuilding the indexes or they were in an old version format. Either way, we
started from scratch as we couldn't guarantee that it was fixing itself.

Then a filled index partition, recovering the space and restarting dovecot
didn't get us anywhere, pop downloads were still failing and dieing.

The last two issues have just been plain odd.  Massive volumes of mail
arriving to pop accounts, imap sessions working fine but pop downloads
dieing after a few seconds.

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.

Regards

John