[Dovecot] Difference between Indexing and Rescan in FTS

[Fred Kilbourn]

> -----Original Message-----
> From: dovecot-bounces at dovecot.org [mailto:dovecot-bounces at dovecot.org]
> On Behalf Of Jack Bates
> Sent: Tuesday, October 16, 2012 9:44 PM
> To: dovecot at dovecot.org
> Subject: Re: [Dovecot] Difference between Indexing and Rescan in FTS
> 
> On 10/16/2012 6:14 PM, Fred Kilbourn wrote:
> > I've had squat running on dovecot 2.0 and have been updating all users
> > mailbox indexes nighty via cron with this command:
> >
> > doveadm -v search -A text xyzzyx
> >
> >
> >
> > I've just updated to 2.1 and I'm migrating to lucene indexes, but
reading
> > the documentation I'm having a hard time understanding the semantic
> > differences between indexing and rescanning.
> >
> >
> >
> > If I were to continue to run an all user all mailbox index every night,
> > would that be appropriate?
> >
> >
> >
> > Would running this every night avoid the need to ever rescan?
> >
> >
> 2 sets of indexes.
> 
> dovecot indexes
> FTS indexes
> 
> Performing the cron search will update the FTS indexes, although you
> should read up on 2.1's doveadm index command. The dovecot indexes
> should stay in sync. However, if they do lose track of the FTS indexes,
> you can do a rescan to sync them back up. Except for corruption or index
> changes made outside of dovecot, the two sets of indexes should stay in
> sync.
> 
> 
> Jack

Thanks Jack,

So here are my takeaways, let me know if I'm wrong:
- The FTS index is the actual search data
- The dovecot index holds, among other information, which messages are
indexed by FTS
- The FTS index still doesn't update automatically, so my nightly cronjob
should keep it in order
- The dovecot index should stay in order under normal circumstances, and
issuing a resync command shouldn't be needed unless something bad happens

Assuming my understanding above is correct, how about these questions, to
further clarify my original questions:
- As a system administrator, what signs should I look for that a resync is
needed? (aside from user complaints)
- What exact impact does running the resync command have?
- Is it worthwhile to resync periodically as a maintenance task?
- Or, does resyncing reset all FTS indexing that has been done, causing it
to have to be done again from scratch?

And, I did catch the revision in the user docs for updating indexes.  I plan
on updating my maintenance script accordingly.

Thanks,
Fred