From: Junio C Hamano <gitster@pobox.com>
To: Patrick Steinhardt <ps@pks.im>
Cc: git@vger.kernel.org,
Christian Couder <christian.couder@gmail.com>,
Jeff King <peff@peff.net>
Subject: Re: [PATCH v2 4/4] fetch: implement support for atomic reference updates
Date: Tue, 12 Jan 2021 11:19:49 -0800 [thread overview]
Message-ID: <xmqqturm3qui.fsf@gitster.c.googlers.com> (raw)
In-Reply-To: <X/2UkKS0AhT6jLXj@ncase> (Patrick Steinhardt's message of "Tue, 12 Jan 2021 13:22:40 +0100")
Patrick Steinhardt <ps@pks.im> writes:
>>
>> > > + fprintf(fetch_head->fp, "%s\t%s\t%s",
>> > > + old_oid, merge_status_marker, note);
>> > > + for (i = 0; i < url_len; ++i)
>> > > + if ('\n' == url[i])
>> > > + fputs("\\n", fetch_head->fp);
>> > > + else
>> > > + fputc(url[i], fetch_head->fp);
>> > > + fputc('\n', fetch_head->fp);
>>
>> ... these stdio operations for a single record would result in a
>> single atomic write() that would not compete with writes by other
>> processes. So I wouldn't call "the current design allows ... at the
>> same time." It has been broken for years and nobody complained.
>
> Fair enough. I somehow blindly assumed that `git fetch --all`, which
> does invoke `git fetch --append`, did perform the fetch in parallel. If
> that's not the case: all the better.
The "--all" option started as "one after another, one at a time",
but these days goes thru fetch_multiple() where we started to use
run_processes_parallel() API without giving it much thought what it
would do to the writing of FETCH_HEAD; since around d54dea77 (fetch:
let --jobs=<n> parallelize --multiple, too, 2019-10-05), this
codepath wrt FETCH_HEAD is utterly broken, I would have to say.
> The buffering of a single line is exactly what we're doing now in the
> non-atomic case. Previously there had been multiple writes, now we only
> call `strbuf_write()` once on the buffer for each reference.
Exactly.
next prev parent reply other threads:[~2021-01-12 19:22 UTC|newest]
Thread overview: 41+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-07 13:51 [PATCH 0/2] fetch: implement support for atomic reference updates Patrick Steinhardt
2021-01-07 13:51 ` [PATCH 1/2] fetch: allow passing a transaction to `s_update_ref()` Patrick Steinhardt
2021-01-07 22:59 ` Junio C Hamano
2021-01-08 0:45 ` Christian Couder
2021-01-08 7:18 ` Junio C Hamano
2021-01-07 13:51 ` [PATCH 2/2] fetch: implement support for atomic reference updates Patrick Steinhardt
2021-01-08 0:19 ` Junio C Hamano
2021-01-08 12:11 ` [PATCH v2 0/4] " Patrick Steinhardt
2021-01-08 12:11 ` [PATCH v2 1/4] fetch: extract writing to FETCH_HEAD Patrick Steinhardt
2021-01-08 23:40 ` Junio C Hamano
2021-01-11 10:26 ` Patrick Steinhardt
2021-01-11 19:24 ` Junio C Hamano
2021-01-08 12:11 ` [PATCH v2 2/4] fetch: refactor `s_update_ref` to use common exit path Patrick Steinhardt
2021-01-08 23:50 ` Junio C Hamano
2021-01-11 10:28 ` Patrick Steinhardt
2021-01-08 12:11 ` [PATCH v2 3/4] fetch: allow passing a transaction to `s_update_ref()` Patrick Steinhardt
2021-01-08 23:53 ` Junio C Hamano
2021-01-08 12:11 ` [PATCH v2 4/4] fetch: implement support for atomic reference updates Patrick Steinhardt
2021-01-09 0:05 ` Junio C Hamano
2021-01-11 10:42 ` Patrick Steinhardt
2021-01-11 19:47 ` Junio C Hamano
2021-01-12 12:22 ` Patrick Steinhardt
2021-01-12 12:29 ` Patrick Steinhardt
2021-01-12 19:19 ` Junio C Hamano [this message]
2021-01-11 11:05 ` [PATCH v3 0/5] " Patrick Steinhardt
2021-01-11 11:05 ` [PATCH v3 1/5] fetch: extract writing to FETCH_HEAD Patrick Steinhardt
2021-01-11 23:16 ` Junio C Hamano
2021-01-11 11:05 ` [PATCH v3 2/5] fetch: use strbuf to format FETCH_HEAD updates Patrick Steinhardt
2021-01-11 11:10 ` Patrick Steinhardt
2021-01-11 11:17 ` Christian Couder
2021-01-11 23:21 ` Junio C Hamano
2021-01-11 11:05 ` [PATCH v3 3/5] fetch: refactor `s_update_ref` to use common exit path Patrick Steinhardt
2021-01-11 11:05 ` [PATCH v3 4/5] fetch: allow passing a transaction to `s_update_ref()` Patrick Steinhardt
2021-01-11 11:05 ` [PATCH v3 5/5] fetch: implement support for atomic reference updates Patrick Steinhardt
2021-01-12 0:04 ` [PATCH v3 0/5] " Junio C Hamano
2021-01-12 12:27 ` [PATCH v4 " Patrick Steinhardt
2021-01-12 12:27 ` [PATCH v4 1/5] fetch: extract writing to FETCH_HEAD Patrick Steinhardt
2021-01-12 12:27 ` [PATCH v4 2/5] fetch: use strbuf to format FETCH_HEAD updates Patrick Steinhardt
2021-01-12 12:27 ` [PATCH v4 3/5] fetch: refactor `s_update_ref` to use common exit path Patrick Steinhardt
2021-01-12 12:27 ` [PATCH v4 4/5] fetch: allow passing a transaction to `s_update_ref()` Patrick Steinhardt
2021-01-12 12:27 ` [PATCH v4 5/5] fetch: implement support for atomic reference updates Patrick Steinhardt
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