Re: [PATCH 0/2] Accelerate "git merge-base --is-ancestor"

[Abhishek Kumar <abhishekkumar8222@gmail.com>]

On Wed, Jun 17, 2020 at 05:24:27PM +0000, Derrick Stolee via GitGitGadget wrote:
> It was recently [1] reported (and not-so-recently [2] reported) that "git
> merge-base --is-ancestor" can be pretty slow. In fact, it is regularly
> slower than "git branch --contains" or "git tag --contains", which are
> answering a "harder" query.
> 
> [1] https://lore.kernel.org/git/20200607195347.GA8232@szeder.dev/
> 
> [2] https://lore.kernel.org/git/87608bawoa.fsf@evledraar.gmail.com/
> 
> The root cause is that the in_merge_base() implementation is skipping the
> fast can_all_from_reach() implementation and using paint_down_to_common()
> instead. Note that these are equivalent: a commit A is in the set of
> merge-bases between A and B if and only if B can reach A.
> 
> This fixes the issue, and makes the performance degradation reported by
> Szeder a non-issue.
> 
> Thanks, -Stolee
> 
> Derrick Stolee (2):
>   commit-reach: create repo_is_descendant_of()
>   commit-reach: use fast logic in repo_in_merge_base
> 
>  commit-reach.c | 21 ++++++++++++++++++---
>  1 file changed, 18 insertions(+), 3 deletions(-)
> 
> 
> base-commit: b3d7a52fac39193503a0b6728771d1bf6a161464
> Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-664%2Fderrickstolee%2Fmerge-base-is-ancestor-v1
> Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-664/derrickstolee/merge-base-is-ancestor-v1
> Pull-Request: https://github.com/gitgitgadget/git/pull/664
> -- 
> gitgitgadget

Wow! Thanks for investigating through the issue and following up. The
performance numbers speak for themselves.

By applying this series on the commit-slab patch series, both are now
just as fast (master: 0.048s, commit-slab: 0.050s). 

Regards
Abhishek