[Dovecot] Dovecot 1.0-stable mbox performance and disconnections

[Timo Sirainen]

On Tue, 2005-07-12 at 15:37 +0100, Chris Wakelin wrote:
> Doing some perfomance monitoring (with Solaris 8 process accounting), it 
> looks like Dovecot needing to read only 30-50% of the disk blocks needed 
> by UW-IMAP, but I was hoping for better!
> 
> What seems to happen, is that most of the connections use only a small 
> number of blocks (due to Dovecot indexes, presumably) but occassionally 
> a process will read lots of blocks, sometimes even more than a UW-IMAP 
> session.

Most of this probably happens when new mails are appended to mailbox
using some external tool, and after that the mailbox is selected again
in Dovecot (if new mails arrive to selected mailbox,
mbox_dirty_syncs=yes prevents the mbox from being fully re-read).

Another reason why Dovecot might be reading more than UW-IMAP is that
when setting message flags, it reads the mail headers for those mails,
and later when closing the mailbox it writes the flags. Those extra
reads are completely unnecessary and I should fix the code not to do
that..

> Is this expected, or is something going wrong with the index updates? I 
> have the default sync settings, I think (mbox_dirty_syncs = yes, 
> mbox_very_dirty_syncs = no, mbox_lazy_writes = yes)

Setting mbox_very_dirty_syncs = yes makes Dovecot not re-read the mbox
entirely when selecting externally modified mbox, unless it notices that
mails aren't where they should be.

> Also, Dovecot seems to be dropping connections, sometimes, for no good 
> reason (putting some extra i_info lines suggests for "inactivity"). 
> Thunderbird tends to reconnect automatically, though. It seems it may be 
> happening at the end of an IDLE command, something like:-

Hmm.. Dovecot closes the connection because of inactivity? How long has
Thunderbird been idling then? It should be disconnected if it doesn't
say anything for 30 minutes, but not before that.

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