[Dovecot] SIS Implementation

[Eric Jon Rostetter]

Quoting Timo Sirainen <tss at iki.fi>:

> 1) When writing the data, extract the attachments and write them to
> different files. Add pointers to those files to the EXT_REF metadata.
> Dovecot's message parsers should make this not-too-difficult to
> implement.

I'd rather it did mime parts, rather than attachments.  In my use case,
we don't get attachments distrubuted as widely as we get messages
distributed.  If the local mailbox had the headers, but the SIS area
had the mime parts, this would save tons of space.  Since attachments
are mime-parts, this works for both cases...

> 3) Once that works, figure out a way to implement SIS for those
> externally written files. Creating hard links to files a global
> attachment storage would probably be a workable solution. Then scan
> through the storage once in a while and delete files with link count=1.

Hardlinks is one way, for filesystems that support it.  But it does have
limits (can't span volumes, etc).

But any kind of setup that can maintain the file and a usage count should
work (and the two don't have to be kept together, though they can).  If you
add a management interface, all the better.

BTW, PMDF implemented all this eons ago (in their popstore I think it was)
system added around PMDF 5 or 6....  Was actually pretty nice, in particular
for the times (this was the 1990's).

Anyway, my $0.02 worth, not that I'm waiting on this feature, but it sure
would save me tons of disk space if I had it...

-- 
Eric Rostetter
The Department of Physics
The University of Texas at Austin

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