Re: Git gc removes all packs

> On Thu, Feb 05, 2015 at 04:13:03PM +0100, Dmitry Neverov wrote:
>
>> I'm using git p4 for synchronization with perforce. Sometimes after 'git
>> p4 rebase' git starts a garbage collection. When gc finishes a local
>> repository contains no pack files only loose objects, so I have to
>> re-import repository from perforce. It also doesn't contain a temporary
>> pack git gc was creating.
>
> It sounds like git didn't find any refs; it will pack only objects which
> are reachable. Unreachable objects are either:
>
>   1. Exploded into loose objects if the mtime on the pack they contain
>      is less than 2 weeks old (and will eventually expire when they
>      become 2 weeks old).
>
>   2. Dropped completely if older than 2 weeks.
>
>> One more thing about my setup: since git p4 promotes a use of a linear
>> history I use a separate repository for another branch in perforce. In
>> order to be able to cherry-pick between repositories I added this
>> another repo objects dir as an alternate and also added a ref which is a
>> symbolic link to a branch in another repo (so I don't have to do any
>> fetches).
>
> You can't symlink refs like this. The loose refs in the filesystem may
> be migrated into the "packed-refs" file, at which point your symlink
> will be broken. That is a likely reason why git would not find any refs.
>
> So your setup will not ever work reliably.  But IMHO, it is a bug that
> git does not notice the broken symlink and abort an operation which is
> computing reachability in order to drop objects. As you noticed, it
> means a misconfiguration or filesystem error results in data loss.
>
> -Peff