Re: fact-import: failed to apply delta

["Shawn O. Pearce" <spearce@spearce.org>]

Daniel Barkalow <barkalow@iabervon.org> wrote:
> 
> I think maybe there's aliasing in the delta base cache? If it recycled a 
> struct packed_git, the cache would come up with a cached tree at offset 12 
> of the packed_git at that address, but the pack used by that struct has 
> changed.

Yup, that must be it.
 
> I don't see any reason that the situation couldn't arise where you start a
> pack, look up an object in it while it's still open but the object isn't 
> in the window, cache the delta base, end that packfile, eventually start a 
> packfile that gets allocated in the space that was freed, produce a new 
> delta against the object at exactly the same offset of the new pack (with 
> the same address as the old pack), and go on happily until you try looking 
> up this last delta and pull the wrong base out of the cache.
> 
> I don't see any code to flush the delta cache ever, but it's hard to get a 
> new packed_git allocated at the address of a freed one, except by doing a 
> lot of checkpoints in fast-import...

*ouch*.  I think you found it.

We should dump the cached_objects table in sha1_file.c during
a checkpoint in fast-import.

-- 
Shawn.