Re: [PATCH 2/2] line-log: avoid unnecessary full tree diffs

From: Junio C Hamano <gitster@pobox.com>
To: "SZEDER Gábor" <szeder.dev@gmail.com>
Cc: git@vger.kernel.org, Thomas Rast <tr@thomasrast.ch>,
	Derrick Stolee <stolee@gmail.com>
Subject: Re: [PATCH 2/2] line-log: avoid unnecessary full tree diffs
Date: Wed, 21 Aug 2019 10:29:11 -0700	[thread overview]
Message-ID: <xmqqtvaas9zs.fsf@gitster-ct.c.googlers.com> (raw)
In-Reply-To: <20190821110424.18184-3-szeder.dev@gmail.com> ("SZEDER =?utf-8?Q?G=C3=A1bor=22's?= message of "Wed, 21 Aug 2019 13:04:24 +0200")

SZEDER Gábor <szeder.dev@gmail.com> writes:

> So basically the line-level log computes a full tree diff for each
> commit-parent pair in step (1) to be used for rename detection in step
> (4) in the off chance that an interesting path is missing from the
> parent.

Good explanation.  As we are not supporting swapping of two (or
more) files, we only need rename processing when a path we have been
inspecting disappears, at which point it is worth spending cycles to
see where the path used to be in the parent commit.

> [1] Line-level log's rename following is quite similar to 'git log
>     --follow path', with the notable differences that it does handle
>     multiple paths at once as well, and that it doesn't show the
>     commit performing the rename if it's an exact rename.

Yeah, it's one of the reasons why "log --follow" is not (yet) a
serious "feature" but merely a "checkbox item".

> [2] This slowness might not have been apparent initially, because back
>     when the line-level log feature was introduced rename detection

s/introduced/&,/

>     was not yet enabled by default; 12da1d1f6f (Implement line-history
>     search (git log -L), 2013-03-28) and 5404c116aa (diff: activate
>     diff.renames by default, 2016-02-25).

s/\.$/ are about 3 years apart&/ or something like that to make what
follows the semicolon a full sentence?