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

From: Theodore Tso <tytso@mit.edu>
Date: Dec 15, 2008, 15:56 UTC
Message-ID: <20081215155610.GA11502@mit.edu>
In-Reply-To: <20081215140834.GA3684@atjola.homenet>

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