[Dovecot] Duplicate Attachments....

[Timo Sirainen]

On Thu, 2006-06-01 at 09:10 -0400, Tore André Klock wrote:
> Timo Sirainen wrote:
> > I think that could anyway be a good idea, but how about hash collisions?
> > I could just ignore that since they would practically never happen. Hash
> > + attachment size would be even safer. The only truly safe way would be
> > to read the whole attachment from disk and compare it byte-by-byte, but
> > that'd just slow it down unneededly.. Perhaps it should be an option.
> Collisions won't be a big problem if you use something like SHA, but it would be
> slow.  You have to generate a checksum for both sides of the comparison, meaning
> you have to generate it at least once per message.  Generating it always means
> reading every byte of it.

The delivered mail's every byte has to be read anyway, and for the
stored attachment the filename would already contains the checksum. I
don't think it takes too much extra time to calculate the attachment's
checksum while it's being read.

> A better solution might be for the LDA to detect which messages are being
> delivered locally to more than one user.  

That's what I was originally thinking instead of checksums.

> I could then make the message file
> shared (in the case of Maildir anyway), for example by hard-linking the files.
> The message would then exist on disk in one copy until each client have removed
> it (bringing the link count to 0).

One problem that I see with hardlinking maildir files is that then you
can't have Delivered-To (or similar) header separate for each user. I
don't know if that's a real problem though..
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