Re: [PATCH] gc: do not warn about too many loose objects

From: Jonathan Nieder <jrnieder@gmail.com>
Date: Jul 16, 2018, 19:19 UTC
Message-ID: <20180716191923.GC11513@aiede.svl.corp.google.com>
In-Reply-To: <20180716191505.857-1-newren@gmail.com>

Hi,

Elijah Newren wrote:

Show 7 quoted lines

> The basic problem here, at least for us, is that gc has enough
> information to know it could expunge some objects, but because of how
> it is structured in terms of several substeps (reflog expiration,
> repack, prune), the information is lost between the steps and it
> instead writes them out as unreachable objects.  If we could prune (or
> avoid exploding) loose objects that are only reachable from reflog
> entries that we are expiring, then the problem goes away for us.

My understanding is that exploding the objects is intentional behavior, to avoid a race where objects are newly referenced while they are being pruned.

I am not a fan of that behavior. It's still racy. But when we've brought it up in the past, the consensus seems to have been that it's better than nothing. Documentation/technical/hash-function-transition.txt section "Loose objects and unreachable objects" describes a way to eliminate the race.

Thanks and hope that helps, Jonathan