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From: "Derrick Stolee via GitGitGadget" <gitgitgadget@gmail.com>
To: git@vger.kernel.org
Cc: Michael Haggerty <mhagger@alum.mit.edu>,
	me@ttaylorr.com, peff@peff.net, gitster@pobox.net,
	Derrick Stolee <derrickstolee@github.com>
Subject: [PATCH 0/3] Speed up remove_redundant()
Date: Thu, 28 Jan 2021 16:24:51 +0000	[thread overview]
Message-ID: <pull.852.git.1611851095.gitgitgadget@gmail.com> (raw)

Michael Haggerty pointed out that git merge-base --independent is quite slow
when many commits are provided in the input. This boils down to some
quadratic behavior in remove_redundant() because it calls
paint_down_to_common() in a loop.

This series avoids that by using a single commit walk, pushing a flag that
means "this commit is reachable from a parent of a commit in the list." At
the end of the walk, the input commits without that flag are independent.

There is an extra performance enhancement using the first-parent history as
a heuristic. This helps only when there is a single independent result, as
we can short circuit the walk when all other inputs are found to be
reachable from the top one.

My tests were on the Linux kernel repository, testing this command:

  git merge-base --independent $(git for-each-ref refs/tags --format="%(refname)")

       Before: 16.4s
After Patch 1:  1.1s
After Patch 2:  0.1s

This does not change the correctness of the function. It is tested carefully
in t6600-test-reach.c, among existing merge-base tests.

Thanks, -Stolee

Derrick Stolee (3):
  commit-reach: use one walk in remove_redundant()
  commit-reach: move compare_commits_by_gen
  commit-reach: use heuristic in remove_redundant()

 commit-reach.c | 178 +++++++++++++++++++++++++++++++++----------------
 1 file changed, 120 insertions(+), 58 deletions(-)


base-commit: 5a3b130cad0d5c770f766e3af6d32b41766374c0
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-852%2Fderrickstolee%2Fmerge-independent-v1
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-852/derrickstolee/merge-independent-v1
Pull-Request: https://github.com/gitgitgadget/git/pull/852
-- 
gitgitgadget

             reply	other threads:[~2021-01-28 16:26 UTC|newest]

Thread overview: 36+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-01-28 16:24 Derrick Stolee via GitGitGadget [this message]
2021-01-28 16:24 ` [PATCH 1/3] commit-reach: use one walk in remove_redundant() Derrick Stolee via GitGitGadget
2021-01-28 20:51   ` Junio C Hamano
2021-01-29 17:11     ` René Scharfe
2021-01-31  3:52       ` Derrick Stolee
2021-01-31 10:20         ` René Scharfe
2021-01-31  3:59     ` Derrick Stolee
2021-01-31 20:13       ` Derrick Stolee
2021-01-31 20:25       ` Junio C Hamano
2021-02-01  3:55         ` Derrick Stolee
2021-01-29 17:10   ` René Scharfe
2021-01-28 16:24 ` [PATCH 2/3] commit-reach: move compare_commits_by_gen Derrick Stolee via GitGitGadget
2021-01-28 16:24 ` [PATCH 3/3] commit-reach: use heuristic in remove_redundant() Derrick Stolee via GitGitGadget
2021-01-28 20:20 ` [PATCH 0/3] Speed up remove_redundant() Junio C Hamano
2021-02-01 12:47 ` [PATCH v2 0/5] " Derrick Stolee via GitGitGadget
2021-02-01 12:47   ` [PATCH v2 1/5] commit-reach: reduce requirements for remove_redundant() Derrick Stolee via GitGitGadget
2021-02-01 19:51     ` Junio C Hamano
2021-02-01 12:47   ` [PATCH v2 2/5] commit-reach: use one walk in remove_redundant() Derrick Stolee via GitGitGadget
2021-02-01 16:12     ` René Scharfe.
2021-02-01 16:31       ` Derrick Stolee
2021-02-01 12:47   ` [PATCH v2 3/5] commit-reach: move compare_commits_by_gen Derrick Stolee via GitGitGadget
2021-02-01 12:47   ` [PATCH v2 4/5] commit-reach: use heuristic in remove_redundant() Derrick Stolee via GitGitGadget
2021-02-01 20:05     ` Junio C Hamano
2021-02-01 21:02       ` Derrick Stolee
2021-02-01 12:47   ` [PATCH v2 5/5] commit-reach: stale commits may prune generation further Derrick Stolee via GitGitGadget
2021-02-03 15:59     ` Taylor Blau
2021-02-01 15:48   ` [PATCH v2 0/5] Speed up remove_redundant() Derrick Stolee
2021-02-18 23:25     ` Junio C Hamano
2021-02-19 12:17       ` Derrick Stolee
2021-02-20  3:32         ` Junio C Hamano
2021-02-19 12:34   ` [PATCH v3 " Derrick Stolee via GitGitGadget
2021-02-19 12:34     ` [PATCH v3 1/5] commit-reach: reduce requirements for remove_redundant() Derrick Stolee via GitGitGadget
2021-02-19 12:34     ` [PATCH v3 2/5] commit-reach: use one walk in remove_redundant() Derrick Stolee via GitGitGadget
2021-02-19 12:34     ` [PATCH v3 3/5] commit-reach: move compare_commits_by_gen Derrick Stolee via GitGitGadget
2021-02-19 12:34     ` [PATCH v3 4/5] commit-reach: use heuristic in remove_redundant() Derrick Stolee via GitGitGadget
2021-02-19 12:34     ` [PATCH v3 5/5] commit-reach: stale commits may prune generation further Derrick Stolee via GitGitGadget

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