Corrupted sizes in cache once again

Tim Evers te-ml-ext at
Thu Feb 2 15:57:37 UTC 2023

Am 02.02.23 um 16:23 schrieb Aki Tuomi:
>> On 02/02/2023 17:19 EET Stuart Henderson <stu at> wrote:
>> On 2023-02-01, Tim Evers <te-ml-ext at> wrote:
>>> I run a fairly large Dovecot Installation (around 100k mailboxes) on
>>> several servers.
>>> gzip compression is on.
>>> Every once in a while I get the dreaded "cache corruption" messages in
>>> the log:
>>> Error: Corrupted record in index cache file
>>> /[redacted]/Maildir/dovecot.index.cache: UID 3868: Broken physical size
>>> in mailbox INBOX:
>>> read(zlib(/[redacted]/Maildir/cur/1674129792.M797543P21755.node2,S=8099,W=8276:2,))
>>> failed: Cached message size smaller than expected (2877 < 8099,
>>> box=INBOX, UID=3868)
>>> Error: Corrupted record in index cache file
>>> /[redacted]/Maildir/dovecot.index.cache: UID 3875: Broken physical size
>>> in mailbox INBOX:
>>> read(zlib(/[redacted]/Maildir/cur/1674212201.M985809P29112.node2,S=13907,W=14121:2,))
>>> failed: Cached message size smaller than expected (5533 < 8192,
>>> box=INBOX, UID=3875)
>>> The first entry shows 2877 (size on disk) vs. 8099 (real size unzipped,
>>> also in the filename: S=8099).
>>> The second entry shows 5533 (size on disk) vs. 8192 - this is not
>>> correct in any way. Size on disk is 13907 as noted in the filename.
>>> Both mails were delivered trough LMTP and retrieved by the POP3 service.
>>> Anyone with an idea what might be happening here? I've read all
>>> available info in the doc and in the previous discussions / bug reports,
>>> but nothing seems to match my case. And where does that 8192 come from -
>>> it looks suspicious?
>>> Version is (Ubuntu 20.04)
>> is rather old now. There were definitely fixes regarding compression
>> around the 2.3.10-2.3.12 timeframe or thereabouts (I forget all the details
>> but it took a release or two before some remaining issues were sorted out
>> after changes in the area). I'd be looking to get it updated to a current
>> version first.
> For bug reports, we do ask that you try to reproduce it with 2.3.20 (current latest), you can get packages from and would be nice if you can provide steps to reproduce this issue.
> Also please see if you have not yet.
> Aki

This is not a bug report (yet) - I am asking for ideas to narrow down 
the issue myself. I would not expect something this obvious and 
prevalent being a bug in a 10+ years old subsystem (zlib).


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