From: Jonathan Nieder <jrnieder@gmail.com>
Date: Fri, 23 May 2014 18:24:29 GMT
Subject: Re: [PATCH v8 41/44] refs.c: add a new flag for transaction delete for refs we know are packed only
Message-ID: <20140523182429.GD12314@google.com>
In-Reply-To: <CAL=YDWnRkwX3dCv9dyZmBdh2ZV7aSUCS=F6w67gJuBmCzGGBwQ@mail.gmail.com>

Ronnie Sahlberg wrote:
> On Thu, May 22, 2014 at 4:53 PM, Jonathan Nieder <jrnieder@gmail.com> wrote:

>> ... or is the problem that the reflogs conflict?
>>
>> How does rename_ref handle propagating the reflog from the old
>> name to the new name, by the way?
>
> I haven't touched that yet, but we can fix it after the next series
> when we have transaction support for reflogs.
>
> It still renames the reflog via the magic name
> #define TMP_RENAMED_LOG  "logs/refs/.tmp-renamed-log"

Okay, after looking at what "git branch -m" currently does (deletes
the old ref and creates the new one in separate transactions), I'm
convinced that this take-locks-for-a-shorter-period-than-is-necessary
trick is an improvement relative to the status quo.  It gets rid of
the window with objects unreferenced between the ref deletion and ref
creation, which is a nice improvement.

I still haven't looked closely at the details of the code change but
the idea looks sane as a first step.

Later we can try to get the semantics right for this kind of
delete/create pair in general transactions, if someone is interested.
:)  No need for the perfect to be the enemy of the good in the
meantime.

Thanks,
Jonathan