Re: [PATCH 2/4] read-cache: add index.skipHash config option

> The previous change allowed skipping the hashing portion of the
> hashwrite API, using it instead as a buffered write API. Disabling the
> hashwrite can be particularly helpful when the write operation is in a
> critical path.
>
> One such critical path is the writing of the index. This operation is so
> critical that the sparse index was created specifically to reduce the
> size of the index to make these writes (and reads) faster.
>
> Following a similar approach to one used in the microsoft/git fork [1],
> add a new config option (index.skipHash) that allows disabling this
> hashing during the index write. The cost is that we can no longer
> validate the contents for corruption-at-rest using the trailing hash.
> [...]
> Signed-off-by: Derrick Stolee <derrickstolee@github.com>
> ---
> diff --git a/Documentation/config/index.txt b/Documentation/config/index.txt
> @@ -30,3 +30,11 @@ index.version::
> +index.skipHash::
> +       When enabled, do not compute the trailing hash for the index file.
> +       Instead, write a trailing set of bytes with value zero, indicating
> +       that the computation was skipped.
> ++
> +If you enable `index.skipHash`, then older Git clients may report that
> +your index is corrupt during `git fsck`.

> diff --git a/t/t1600-index.sh b/t/t1600-index.sh
> @@ -65,6 +65,14 @@ test_expect_success 'out of bounds index.version issues warning' '
> +test_expect_success 'index.skipHash config option' '
> +       (
> +               rm -f .git/index &&
> +               git -c index.skipHash=true add a &&
> +               git fsck
> +       )
> +'