Re: [PATCH v2 0/6] Sparse Index: Integrate with merge, cherry-pick, rebase, and revert

>
> This series integrates the sparse index with commands that perform merges
> such as 'git merge', 'git cherry-pick', 'git revert' (free with
> cherry-pick), and 'git rebase'.
>
> When the ORT merge strategy is enabled, this allows most merges to succeed
> without expanding the sparse index, leading to significant performance
> gains. I tested these changes against an internal monorepo with over 2
> million paths at HEAD but with a sparse-checkout that only has ~60,000 files
> within the sparse-checkout cone. 'git merge' commands went from 5-6 seconds
> to 0.750-1.250s.
>
> In the case of the recursive merge strategy, the sparse index is expanded
> before the recursive algorithm proceeds. We expect that this is as good as
> we can get with that strategy. When the strategy shifts to ORT as the
> default, then this will not be a problem except for users who decide to
> change the behavior.
>
> Most of the hard work was done by previous series, such as
> ds/sparse-index-ignored-files (which this series is based on).
>
>
> Updates in V2
> =============
>
>  * The tests no longer specify GIT_TEST_MERGE_ALGORITHM or directly
>    reference "-s ort". By relaxing this condition, I found an issue with
>    'git cherry-pick' and 'git rebase' when using the 'recursive' algorithm
>    which is fixed in a new patch.
>
>  * Use the pul.twohead config to specify the ORT merge algorithm to avoid
>    expanding the sparse index when that is what we are testing.