Re: gc considered dangerous

From: Robin Rosenberg <robin.rosenberg.lists@dewire.com>
Date: Feb 8, 2009, 16:04 UTC
Message-ID: <200902081704.59439.robin.rosenberg.lists@dewire.com>
In-Reply-To: <alpine.DEB.1.00.0902081551290.10279@pacific.mpi-cbg.de>

söndag 08 februari 2009 15:56:38 skrev Johannes Schindelin:

Show 8 quoted lines

> Hi,
> 
> On Sun, 8 Feb 2009, Robin Rosenberg wrote:
> 
> > I've seen this. Running git gc on Windows, while having Elipse open can 
> > kill your object database.
> 
> You had me really scared with the mail subject!

Losing a repo *is* scary., especially if your boss is the one losing it. That should simply not happen unless there is a disk failure. Fortunately I believe the two lost branches did not contain anything useful.

Show 6 quoted lines

> > if gc doesn't find a new optimal pack it tries to rewrite a new pack 
> > with the same id. So it rm's the idx file (fine) and the the pack file 
> > (not ok) and gives up,
> 
> I disagree with your notion that it is fine to kill the existing idx file 
> until the new one has been written successfully.

Then you misunderstood me. I meant that the repack script thought it was fine.

> My preliminary guess is that this code in pack-write.c needs to use the 
> lock file paradigm:

Show 7 quoted lines

> 
>         if (!index_name) {
> 		[...]
>         } else {
>                 unlink(index_name);
>                 fd = open(index_name, O_CREAT|O_EXCL|O_WRONLY, 0600);
>         }

Yeah, it needs to check that it can actually delete both files before actually doing it. Then again if it wants to replace a file with a new one just like it, why shouldn't it just skip it. Isn't that the only case I see where we can lose data?

GC should also notice that something is not right when there are old-files present.

-- robin