DBLocker / High Load / IMP ... ?
mika.iisakkila at pingrid.fi
Mon Apr 7 11:26:52 EDT 2003
> On Sun, 6 Apr 2003, Elmo Recio wrote:
>>I noticed, however, that when I disable IMP (from a remote machine), the
>>server load goes down significantly. Since I started writing this email,
>>the load on the email server went down from 189 to 8 righ tnow. I
>>noticed somewhere elase on the internet that there was a similar problem
>>with 2.0.16. I am running 2.1.12.
There is an undocumented(?) Cyrus imapd.conf switch:
...which converts all 'list "" *' IMAP commands into
'list "" INBOX*'. If the user has no mailboxes outside INBOX.*,
they (or IMP) won't see any difference, but the performance
impact for Cyrus on Berkeley is dramatic - the former command scans
through the entire database for mailboxes the users has access to,
while the latter doesn't even look outside the user's personal
mailboxes. You can imagine the difference in the number of lock
contentions when there are hundreds of simultaneous users. More
processes have to wait longer, unable to release their locks and the
situation may start to escalate.
Apparently IMP, in at least some configurations, does these commands
quite often even though there is a mailbox prefix setting.
If you have shared mailboxes (or anything the users need
to access outside their INBOX.*) you can't use this, and
it also breaks the list "" * command for admin users (you might
have to rethink some admin scripts).
And as Rob already said, you'd be better off switching to
skiplist and forgetting this kludge, if at all possible.
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