Re: Recovering from repository corruption

["Denis Bueno" <dbueno@gmail.com>]

On Tue, Jun 10, 2008 at 17:48, Linus Torvalds
<torvalds@linux-foundation.org> wrote:
>
>
> On Tue, 10 Jun 2008, Denis Bueno wrote:
>> >
>> > then *if* you have the files
>> >
>> >        .git/objects/32/0bd6e82267b71dd2ca7043ea3f61dbbca16109
>> >        .git/objects/4d/0be2816d5eea5ae2b40990235e2225c1715927
>> >
>> > then those two files are interesting in themselves (most likely they are
>> > not there at all, or are zero-sized, but if you have them, please post
>> > them).
>>
>> They are attached, and they are not zero-sized.
>
> Very interesting.
>
> Both of them look fairly sane as objects (ie random - it's supposed to eb
> zlib-compressed), but both of them have the first 512 bytes *identically*
> corrupted:
>
>        0000000 6564 626e 6575 406e 6f64 6f72 6874 2e79
>                  d   e   n   b   u   e   n   @   d   o   r   o   t   h   y   .
>        0000020 6f6c 6163 2e6c 3634 0033 0000 0000 0000
>                  l   o   c   a   l   .   4   6   3  \0  \0  \0  \0  \0  \0  \0
>        0000040 0000 0000 0000 0000 0000 0000 0000 0000
>                 \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0
>        *
>
> ie it's an all-zero block, except for that email-looking thing at the
> head.

Right --- that's my username and computer's hostname... for some
reason.  [You are not expected to understand this.  My computer's name
mysteriously changed.  It should not be "dorothy.local" but it is.  I
will have to find out why....]

> One thign that strikes me is that you seem to be really prone to this
> problem, since it happened to you a year ago too. I cannot swear to this,
> but I literally suspect your last case (July-2007) was the previous time
> we had a corruption issue. Why does it seem to happen to you, but not
> others?

It is the same computer on which the problem occurred last time.  It's
an OS X 10.4 macbook pro.  I haven't noticed corruption in other
places, but it's fair to assume it's occurring.  I'll have to boot off
my install disk and fsck the drive....

> Do you have some odd filesystem in play? Was the current corruption in a
> similar environment as the old one? IOW, I'm trying to find a pattern
> here, to see if there might be something we can do about it..

I can't remember if the old one happened after a panic or not, but I'd
bet it did.  The filesystem is HFS+, as indeed most OS X 10.4
installations are.  Maybe the HD has been going south?  However, that
doesn't seem likely, since when I got the computer it was new, and
that was around Jun 2007.

> But it *sounds* like the objects you lost were literally old ones, no? Ie
> the lost stuff wasn't something you had committed in the last five minutes
> or so? If so, then you really do seem to have a filesystem that corrupts
> *old* files when it crashes. That's fairly scary. What FS is it?

No, in fact I had just committed those changes not 10 minutes before
the panic.  Last time they were also fresh changes, although perhaps
older than 10 minutes.  I can't remember.


-- 
 Denis