From: Junio C Hamano <gitster@pobox•com>
To: Michael Haggerty <mhagger@alum•mit.edu>
Cc: "Stefan Beller" <sbeller@google•com>,
"Ronnie Sahlberg" <ronniesahlberg@gmail•com>,
"Jonathan Nieder" <jrnieder@gmail•com>,
"Nguyễn Thái Ngọc" <pclouds@gmail•com>,
"git@vger•kernel.org" <git@vger•kernel.org>,
"Carlos Martín Nieto" <cmn@elego•de>
Subject: Re: [PATCH 8/8] reflog_expire(): lock symbolic refs themselves, not their referent
Date: Fri, 13 Feb 2015 13:53:08 -0800 [thread overview]
Message-ID: <xmqq3869mqbf.fsf@gitster.dls.corp.google.com> (raw)
In-Reply-To: <54DE5A72.6030106@alum.mit.edu> (Michael Haggerty's message of "Fri, 13 Feb 2015 21:11:30 +0100")
Michael Haggerty <mhagger@alum•mit.edu> writes:
> Now back to the real world. Currently, if R is changed *through* a
> symbolic reference S, then the reflogs for both R and S are updated, but
> not the reflogs for any other symbolic references that might point at R.
> If R is changed directly, then no symref's reflogs are affected, except
> for the special case that HEAD's reflog is changed if it points directly
> at R. This limitation is a hack to avoid having to walk symrefs
> backwards to find any symrefs that might be pointing at R.
Yup.
> It might actually not be extremely expensive to follow symrefs
> backwards. Symbolic references cannot be packed, so we would only have
> to scan the loose references; we could ignore packed refs. But it would
> still be a lot more expensive than just updating one file. I don't know
> that it's worth it, given that symbolic references are used so sparingly.
I personally do not think it is worth it. I further think that it
would be perfectly OK to do one of the following:
- We only maintain reflogs for $GIT_DIR/HEAD; no other symrefs
get their own reflog, and we only check $GIT_DIR/HEAD when
updating refs/heads/* and no other refs for direct reference
(i.e. HEAD -> refs/something/else -> refs/heads/master symref
chain is ignored).
- In addition to the above, we also maintain reflogs for
$GIT_DIR/refs/remotes/*/HEAD but support only when they
directly point into a remote tracking branch in the same
hierarchy. $GIT_DIR/refs/remotes/foo/HEAD that points at
$GIT_DIR/refs/remotes/bar/master is ignored and will get an
undefined behaviour.
> I think that the rule about locks as expressed above can be carried over
> the the real world:
>
> We should hold the locks on exactly those references (symbolic
> or regular) whose reflogs we plan to change. We should acquire all
> of the locks before making any changes.
Sure.
next prev parent reply other threads:[~2015-02-13 21:53 UTC|newest]
Thread overview: 46+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-02-09 9:12 [PATCH 0/8] Fix some problems with reflog expiration Michael Haggerty
2015-02-09 9:12 ` [PATCH 1/8] write_ref_sha1(): remove check for lock == NULL Michael Haggerty
2015-02-10 22:52 ` Stefan Beller
2015-02-11 0:06 ` Jeff King
2015-02-09 9:12 ` [PATCH 2/8] write_ref_sha1(): Move write elision test to callers Michael Haggerty
2015-02-12 19:58 ` Junio C Hamano
2015-02-09 9:12 ` [PATCH 3/8] lock_ref_sha1_basic(): do not set force_write for missing references Michael Haggerty
2015-02-10 23:24 ` Stefan Beller
2015-02-11 0:05 ` Jeff King
2015-02-11 0:07 ` Stefan Beller
2015-02-12 12:09 ` Michael Haggerty
2015-02-09 9:12 ` [PATCH 4/8] reflog: fix documentation Michael Haggerty
2015-02-10 23:25 ` Stefan Beller
2015-02-09 9:12 ` [PATCH 5/8] reflog: rearrange the manpage Michael Haggerty
2015-02-10 23:42 ` Stefan Beller
2015-02-12 15:17 ` Michael Haggerty
2015-02-12 20:09 ` Junio C Hamano
2015-02-09 9:12 ` [PATCH 6/8] reflog_expire(): ignore --updateref for symbolic references Michael Haggerty
2015-02-11 0:44 ` Stefan Beller
2015-02-12 16:08 ` Michael Haggerty
2015-02-12 17:04 ` Stefan Beller
2015-02-12 20:16 ` Junio C Hamano
2015-02-12 21:54 ` Jeff King
2015-02-13 14:34 ` Michael Haggerty
2015-02-09 9:12 ` [PATCH 7/8] reflog_expire(): never update a reference to null_sha1 Michael Haggerty
2015-02-09 20:55 ` Eric Sunshine
2015-02-12 11:51 ` Michael Haggerty
2015-02-09 9:12 ` [PATCH 8/8] reflog_expire(): lock symbolic refs themselves, not their referent Michael Haggerty
2015-02-11 0:49 ` Stefan Beller
2015-02-11 22:49 ` Junio C Hamano
2015-02-11 23:25 ` Stefan Beller
2015-02-12 16:52 ` Michael Haggerty
2015-02-12 18:04 ` Stefan Beller
2015-02-13 16:26 ` Michael Haggerty
2015-02-13 17:16 ` Stefan Beller
2015-02-13 18:05 ` Junio C Hamano
2015-02-13 18:21 ` Stefan Beller
2015-02-13 18:26 ` Junio C Hamano
2015-02-13 18:32 ` Stefan Beller
2015-02-13 19:12 ` Junio C Hamano
2015-02-13 20:11 ` Michael Haggerty
2015-02-13 21:53 ` Junio C Hamano [this message]
2015-02-14 5:58 ` Michael Haggerty
2015-02-09 18:57 ` [PATCH 0/8] Fix some problems with reflog expiration Stefan Beller
2015-02-10 23:12 ` [PATCH] refs.c: get rid of force_write flag Stefan Beller
2015-02-12 15:35 ` Michael Haggerty
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