Re: "git gc" doesn't seem to remove loose objects any more

[Theodore Tso <tytso@mit.edu>]

On Mon, Dec 15, 2008 at 03:08:34PM +0100, Björn Steinbrink wrote:
> To clarify that a bit more: git gc keeps unreachable objects unpacked,
> so that git prune can drop them. And git gc invokes git prune so that
> only unreachable objects older than 2 weeks are dropped.

To be even more explicit, "git gc" will **unpack** objects that have
become unreachable and were currently in packs.  As a result, the
amount of disk space used by a git repository can actually go **up**
dramatically after a "git gc" operation, which could be surprising for
someone who is running close to full on their filesystem, deletes a
number of branches from a tracking repository, and then does a "git
gc" may get a very unpleasant surprise.

A really good repository which shows this is linux-next, since it is
constantly getting rewound, and old branches are reserved via a tag
such as next-20081204.  If you update the your local copy of the
linux-next repository every day, you will accumulate a large number of
these old branch tags.  If you then delete a whole series of them, and
run git-gc, the operation will take quite a while, and the number of
blocks and inodes used will grow significantly.  They will disappear
after a "git prune", but when I do this housekeeping operation, I've
often wished for a --yes-I-know-what-I-am-doing-and-it's-unsafe-but-
just-drop-the-unreachable-objects-cause-this-is-just-a-tracking-repository
option to "git gc".

						- Ted