[Dovecot] keeping indexes in tmpfs

[Timo Sirainen]

On Mon, 2007-04-16 at 10:41 -0400, Justin McAleer wrote:
> Ok, I'll give more detail about the setup. I plan to use the convert 
> plugin to migrate from CommuniGate to dovecot for our ~160,000 accounts. 
> We will probably migrate one domain at a time, letting users basically 
> migrate their mail at first login. But, we will also go through all the 
> domain's accounts logging in to pop3 just to ensure everything gets moved.

OK, that also causes it to read the mailboxes and save the message sizes
to cache files.

> So, for testing, I've copied a few of our domains' mail spools over to 
> the test server and started a script that forks and goes through all 
> their accounts and simply logs in to pop3 and waits for a message list 
> to come back. We have the maildirs being stored on an NFS mount though, 
> and indexes on localdisk, so the only localdisk activity was logging and 
> indexes. 

And reading the mail spools? :)

> I'll try setting both of those options and see how much 
> difference it makes, although I'm not sure that losing mail upon server 
> reset is acceptible for us (disabling fsync).

It could be done pretty easily only for index files by modifying the
sources. I guess another option should be added for this.

> >> Anyway, Timo and others, do you have any thoughts about keeping indexes 
> >> on a tmpfs partition? I realize the obvious issues with this: running 
> >> out of space, and the fact that the partition is lost on reboot. 
> >>     
> >
> > I think memory would be better used for keeping mailbox data cached
> > that's actually useful at the time.
> >   
> 
> Perhaps, but one way or another, we apparently cannot use a simple 
> localdisk for indexes. So, the options are either memory or some sort of 
> raid setup. Since we use maildirs, isn't the disk cache aspect less of a 
> concern?

Depends on how mailboxes are accessed. If message contents are read only
once then I guess it doesn't matter. Probably the worst offender here is
SEARCH TEXT/BODY command.
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