From: Junio C Hamano <gitster@pobox.com>
Date: Tue, 09 Dec 2014 18:47:24 GMT
Subject: Re: [PATCH 07/23] expire_reflog(): use a lock_file for rewriting the reflog file
Message-ID: <xmqqfvcomzib.fsf@gitster.dls.corp.google.com>
In-Reply-To: <54857871.5090805@alum.mit.edu>

Michael Haggerty <mhagger@alum.mit.edu> writes:

> This isn't documented very well. I thought I saw a comment somewhere in
> the code that stated it explicitly, but I can't find it now. In any
> case, my understanding of the locking protocol for reflogs is:
>
>     The reflog for "$refname", which is stored at
>     "$GIT_DIR/logs/$refname", is locked by holding
>     "$GIT_DIR/refs/$refname.lock", *even if the corresponding
>     reference is packed*.
>
> This implies that readers, who don't pay attention to locks, have to be
> prepared for the possibility that the reflog is in the middle of an
> update and that the last line is incomplete. This is handled by
> show_one_reflog_ent(), which discards incomplete lines.

Interesting, as I think I saw Peff did something around that area
recently.

I have some more thought around the "transaction" in general, but
it will be in a separate message.

Thanks.