On 16/07/02 10:42 +0530, Binand Raj S. wrote:
<snip>
> Thaths, why do you recommend taking the system down to single user
> mode? Isn't stopping the mail subsystem enough?
It should be. But you don't want users accessing their mail either.

<snip> 
> Is it? Consider a mailbox with 10,000 mails. With mbox, when the client
> does a STAT command, the POP server needs to open mbox, parse
> it, and then send the response. Whereas with maildirs, the server
> just needs to run stat() in a loop. Or if a single mail is requested, its
> serial no (in the STAT command) is mapped to the filename in Maildir/new,
> so a comparatively smaller file needs to be opened and sent across the
> network.
But there is the overhead of stat(2)ing a lot of files in a single
folder. ext2 is bad at this. xfs is much better.

> Maybe CRLF translation requirement would make it necessary to open all files
> in a Maildir to be opened before their sizes can be determined.
> 
> Also, it seems to me that memory usage etc. of a POP/IMAP server serving
> Maildir mailboxes would be lesser compared to one serving mbox mailboxes.
For pop, it is much less, imap has a higher usage due to the nautre of
the protocol.
 
> I'd like to know what your reasons are in saying both would be equally (?)
> slow when dealing with large mailboxes.
> 
> Thinking about it, are there any benchmarks on the relative performance of
> these two systems out there? Didn't find any on DJB's home page.
stat() on a few thousand files is timeconsuming.
 
> > Cyrus IMAP as well.  It has a non-standard format of storing mail that is
> > sort of like Maildir.  But the problem there would be user's can only read
> > mail through the IMAP (i.e you cannot use mutt locally on the machine to
> > read off /var/spool/mail or ~/Mail).
> 
> The problem with Cyrus would be one of migration - both to and from. Does
> it ship with tools that migrate mbox/Maildir to its database format? Or vice
> versa?
It does come with scripts, the only information lost is the seen info.
Or you could just get users to fetchmail their stuff over into
cyrus/courier/whatever.
imap server -> fetchmail -> MTA running only on 127.0.0.1 and delivering
to your new imap server. Tell users to run a fetchmail script once (down
the mail system for a few hours, get all users to migrate (or reset
everyones passwords) and then simply let the new imapd run).

Devdas Bhagat


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