Re: Problem with pack

[Sergio Callegari <scallegari@arces.unibo.it>]

>
> Andreas Ericsson <ae@op5.se> writes:
>
> >> Btw, even without that, if I understand correctly, git packs are
> >> collections of compressed objects, each of which has its own header
> >> stating how long is the compressed object itself. In my case, the
> >> error is in inflating one object (git unpack-objects says inflate
> >> returns -3)... so shouldn't there be a way to try to skip to the
> >> next object even in this case?
> >
> > It should be possible, assuming the pack index is still intact. The
> > pack index is where the headers are stored, afaik.
>
> The problem Sergio seems to be having is because somehow he does
> not have a base object that another object that is in the pack
> depends on, because the latter object is stored in deltified
> form.
>
> This should never happen unless .pack itself is corrupted
> (git-pack-objects, unless explicitly told to do so with --thin
> flag to git-rev-list upstream, would not make a delta against
> objects not in the same pack).
>
> When a delta is written to the pack file, unless its base object
> has already written out, git-pack-objects writes out the base
> object immediately after that deltified object.  So one
> possibility is that the pack was truncated soon after the delta
> that is having trouble with finding its base object.  In such a
> case, the proposed recovery measure of skipping the corruption
> and keep going would not buy you that much.  On the other hand,
> if the corruption is in the middle (e.g. a single disk block was
> wiped out), having .idx file might help you resync.
>
> Does the pack pass git-verify-pack test, I wonder?
If I try to verify the pack I get:

git verify-pack -v pack-ebcdfbbda07e5a3e4136aa1f499990b35685bab4.idx
fatal: failed to read delta-pack base object 
2849bd2bd8a76bbca37df2a4c8e8b990811d01a7


the package length seems reasonable, however... (no evident sign of 
truncation, but I haven't looked inside the index to check the exact 
positions of objects)...
and git unpack-object dies with error code -3 in inflate...
If I am not wrong (but I might easily be so) this should not be relative 
to truncation...

Sergio