Re: A question about changing remote repo name

From: Junio C Hamano <gitster@pobox.com>
Date: Jan 6, 2010, 01:02 UTC
Message-ID: <7vd41oqc3h.fsf@alter.siamese.dyndns.org>
In-Reply-To: <c1b8b6671001051607j6b6398d8gf08f7615a38de64e@mail.gmail.com>

Russell Steicke <russellsteicke@gmail.com> writes:

> Ah yes, I forgot about those files.  I _think_ (but I'm not certain
> without digging into the code) that it's always safe to rm
> packed-refs, as that file is a cache for quicker access to the refs.

No what you think is incorrect, no it is not safe at all, and no it is not a cache.

refs are created loose as files under $GIT_DIR/refs/. When pack-refs is run (either from the toplevel or as part of gc), these loose ref files are removed and instead written to $GIT_DIR/packed-refs file. When a new ref is created or an existing ref is updated, only $GIT_DIR/refs/ is modified.

When reading or enumerating, a loose ref, if found, is used. Otherwise a record in packed-refs is consulted. The consequences are:

 - If you have $GIT_DIR/refs/heads/master and at the same time, an entry
   for refs/heads/master exists in $GIT_DIR/packed-refs, removing the
   entry in packed-refs happens to be safe, because it was already masked.

 - If you do not have $GIT_DIR/refs/heads/old, but an entry for
   refs/heads/old exists in $GIT_DIR/packed-refs, removing the entry in
   packed-refs means you lose the "old" branch.  You don't want to do
   that.

 - When deleting a ref, we remove it from $GIT_DIR/refs/, but at the same
   time, if packed-refs contains an entry for it, we remove it from
   there.  Otherwise, the removal of the loose one will unmask the stale
   entry in packed-refs file.