[Dovecot] New mailbox format

[John Peacock]

Timo Sirainen wrote:
> The point is to have a mailbox format where the mailbox can consist of one
> or more files. Grouping multiple files in a single file makes it faster to
> read, but it's slower to expunge mails from the beginning of the file. So
> this format would allow sysadmin to specify rules on how large the files
> would be allowed to grow.

This seems like a lot of complexity for an unknown amount of 
performance.  Sure, it is going to be loads faster than multi-megabyte 
mbox mailboxes, but you can color me unconvinced that this will be a 
significant win over maildir.  The primary advantage to maildir is the 
utter simplicity of all operations; at no time do you need to completely 
rewrite any files and all operations are 100% atomic.  The index format 
under maildir is also very simple, since you only need to keep track of 
the filename (and flags) rather than filename and offset and flags.  And 
with modern filesystems, disk access is intelligently cached.

If you are trying to tune for where there are significant numbers of 
very small (< 2k) files (well smaller than the typical block size in the 
underlying filesystem), you may be aiming too small.  It looks like the 
median file size in my maildir folders is about 3100 bytes.  What sizes 
were you thinking the typical admin would set as the limit?

Personally, I think your time would be better spent integrating a 
database message store and let the database engine deal with storage and 
indexing issues.  YMMV. ;-)

John

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John Peacock
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