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From: "Ævar Arnfjörð Bjarmason" <avarab@gmail.com>
To: Git Mailing List <git@vger.kernel.org>
Cc: Thomas Rast <tr@thomasrast.ch>,
	Junio C Hamano <gitster@pobox.com>, Jeff King <peff@peff.net>,
	Johannes Schindelin <Johannes.Schindelin@gmx.de>
Subject: merge-base --is-ancestor A B is unreasonably slow with unrelated history B
Date: Tue, 09 Jan 2018 16:17:41 +0100	[thread overview]
Message-ID: <87608bawoa.fsf@evledraar.gmail.com> (raw)

This is a pathological case I don't have time to dig into right now:

    git branch -D orphan;
    git checkout --orphan orphan &&
    git reset --hard &&
    touch foo &&
    git add foo &&
    git commit -m"foo" &&
    time git merge-base --is-ancestor master orphan

This takes around 5 seconds on linux.git to return 1. Which is around
the same time it takes to run current master against the first commit in
linux.git:

    git merge-base --is-ancestor 1da177e4c3f4 master

This is obviously a pathological case, but maybe we should work slightly
harder on the RHS of and discover that it itself is an orphan commit.

I ran into this while writing a hook where we'd like to do:

    git diff $master...topic

Or not, depending on if the topic is an orphan or just something
recently branched off, figured I could use --is-ancestor as on
optimization, and then discovered it's not much of an optimization.

             reply	other threads:[~2018-01-09 15:17 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-01-09 15:17 Ævar Arnfjörð Bjarmason [this message]
2018-01-09 19:13 ` Junio C Hamano
2018-01-09 19:30 ` Derrick Stolee
2018-01-10 14:01   ` Ævar Arnfjörð Bjarmason

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