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From: Junio C Hamano <gitster@pobox.com>
To: Shawn Pearce <spearce@spearce.org>
Cc: git <git@vger.kernel.org>, Jeff King <peff@peff.net>,
	Michael Haggerty <mhagger@alum.mit.edu>,
	David Borowitz <dborowitz@google.com>
Subject: Re: reftable [v4]: new ref storage format
Date: Wed, 02 Aug 2017 19:36:26 -0700	[thread overview]
Message-ID: <xmqq8tj1qswl.fsf@gitster.mtv.corp.google.com> (raw)
In-Reply-To: <CAJo=hJuWc-hLyTgtdO_AYjUhvRWFSY70bBPEgNtygs5ojJcKyQ@mail.gmail.com> (Shawn Pearce's message of "Wed, 2 Aug 2017 19:21:11 -0700")

Shawn Pearce <spearce@spearce.org> writes:

> On Wed, Aug 2, 2017 at 6:50 PM, Junio C Hamano <gitster@pobox.com> wrote:
> ...
>>    Would it benefit us if we define the sort order of bytes slightly
>>    different from the ASCII order, so that a slash '/' sorts between
>>    NUL '\000' and SOH '\001', which is the order we should have used
>>    when storing the entries in the index?
>
> I'm not really with that. It complicates the compare routine, and
> makes the data in reftable sorted differently than we announce in the
> wire protocol.

Fair enough.  It was not like I had some operations in mind that
would benefit from such a sort order (i.e. walking two of these
things in parallel and merging them, which would have been the case
for the index when we walk it together with one or more trees); if
there is no such operation that benefit, there is no reason to try
to be clever here.

>>  * Even though readers can continue accessing, starting from the
>>    $GIT_DIR/refs, without locking and get consistent views, any
>>    transaction that groups one or more ref updates would need to
>>    take a global lock on $GIT_DIR/refs file.
>>
>>    Would it become a problem in a busy repository?
> ...
>
> I'm not really sure how one could safely do the same thing with
> git-core. Its certainly not going to be portable or safe on NFS if we
> tried to do anything fancy with flock(2), fcntl(F_SETLKW), or
> semop(2).

Yes.

And for public record, another thing we privately discussed was that
we currently do not know if we would want to make this design mesh
well with the use of multiple worktrees (IIUC, HEAD and things
outside refs/, and refs/bisect/, need to be per- worktree, while
others are to be common), and if so how.

  reply	other threads:[~2017-08-03  2:36 UTC|newest]

Thread overview: 34+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-07-31  3:51 Shawn Pearce
2017-07-31 17:41 ` Dave Borowitz
2017-07-31 19:01 ` Stefan Beller
2017-07-31 23:05   ` Shawn Pearce
2017-07-31 19:42 ` Junio C Hamano
2017-07-31 23:43   ` Shawn Pearce
2017-08-01 16:08     ` Shawn Pearce
2017-08-01  6:41 ` Michael Haggerty
2017-08-01 20:23   ` Shawn Pearce
2017-08-02  0:49     ` Michael Haggerty
2017-08-01 23:27   ` Shawn Pearce
2017-08-01 23:54     ` Shawn Pearce
2017-08-02  1:51     ` Michael Haggerty
2017-08-02  2:38       ` Shawn Pearce
2017-08-02  9:28         ` Jeff King
2017-08-02 15:17           ` Shawn Pearce
2017-08-02 16:51             ` Junio C Hamano
2017-08-02 17:28             ` Jeff King
2017-08-02 12:20         ` Dave Borowitz
2017-08-02 17:18           ` Jeff King
2017-08-03 18:38         ` Michael Haggerty
2017-08-03 22:26           ` Shawn Pearce
2017-08-03 22:48             ` Michael Haggerty
2017-08-04  2:50               ` Shawn Pearce
2017-08-05 21:00       ` Shawn Pearce
2017-08-01 13:54 ` Dave Borowitz
2017-08-01 15:27   ` Shawn Pearce
2017-08-02 19:50 ` Junio C Hamano
2017-08-02 20:28   ` Jeff King
2017-08-03 22:17     ` Shawn Pearce
2017-08-03  1:50   ` Junio C Hamano
2017-08-03  2:21     ` Shawn Pearce
2017-08-03  2:36       ` Junio C Hamano [this message]
2017-08-02 19:54 ` Stefan Beller

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