Re: [PATCH v6 1/1] builtin/grep.c: integrate with sparse index

From: Junio C Hamano <gitster@pobox.com>
Date: Sep 23, 2022, 16:40 UTC
Message-ID: <xmqq7d1uvybx.fsf@gitster.g>
In-Reply-To: <20220923041842.27817-2-shaoxuan.yuan02@gmail.com>

Shaoxuan Yuan <shaoxuan.yuan02@gmail.com> writes:

Show 11 quoted lines

> - Command used for testing:
>
> 	git grep --cached bogus -- "f2/f1/f1/*"
>
> The reason for specifying a pathspec is that, if we don't specify a
> pathspec, then grep_tree() will walk all the trees and blobs to find the
> pattern, and the time consumed doing so is not too different from using
> the original ensure_full_index() method, which also spends most of the
> time walking trees. However, when a pathspec is specified, this latest
> logic will only walk the area of trees enclosed by the pathspec, and the
> time consumed is reasonably a lot less.

Good. So without pathspec, we lazily populate the index and catch matches even from outside the sparse cone. We punt to "implicitly" apply the sparse cone(s) as a pathspec that limits the hits to the paths in the sparse cone(s).

> That is, if we don't specify a pathspec, the performance difference [1]
> is indistinguishable: both methods walk all the trees and take generally
> same amount of time (even with the index construction time included for
> ensure_full_index()).

Good.