[Dovecot] Compressed mbox - patch

[Kamil Jońca]

Some time ago I complained about very slow access to compressed mboxes.
Unfortunately it looks like that it is very little interest in it, so I
have to investigate some things by myself.

Firstly: some rationale.
Why do I prefer use mbox/maildir over mdbox. Short answer "bus factor"
for support mdbox (not only dovecot)
Longer answer: if something goes wrong withm maildir/mbox i can use
other tools (mutt, or formail or even text editor) and with mdbox ...

I am not ISP, I use dovecot as a "gateway" to my (rather huge) mail
archive. Most of these mails are rather valuable for me, so I prefer use
something "well-known-and-tested".
(I can't do like most ISP's do: write in "Terms of Service" that mail
can be lost or damaged and we give no warranty :) )

So then:

Below my patch. 
It contains 2 changes:
1. when buffer is compressed, we try to save last marked offset. 
2. Increase temporary buffer for decompression.

without these changes 1.5 GB of bzip compressed mbox with ~20K messages 
can't be open in 1.5 day
After applying 1. change it can be open in ~1.5 h 
With both changes it was a few minutes.

Maybe it is a good idea to add config parameter to specify size of
decompress buffer?


Patch is against v2.0.18


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