Re: [PATCH v2] dir: force untracked cache with core.untrackedCache

[Junio C Hamano <gitster@pobox.com>]

"Derrick Stolee via GitGitGadget" <gitgitgadget@gmail.com> writes:

> From: Derrick Stolee <derrickstolee@github.com>
>
> The GIT_FORCE_UNTRACKED_CACHE environment variable writes the untracked
> cache more frequently than the core.untrackedCache config variable. This
> is due to how read_directory() handles the creation of an untracked
> cache.
>
> Before this change, Git would not create the untracked cache extension
> for an index that did not already have one. Users would need to run a
> command such as 'git update-index --untracked-cache' before the index
> would actually contain an untracked cache.
>
> In particular, users noticed that the untracked cache would not appear
> even with core.untrackedCache=true. Some users reported setting
> GIT_FORCE_UNTRACKED_CACHE=1 in their engineering system environment to
> ensure the untracked cache would be created.
>
> The decision to not write the untracked cache without an environment
> variable tracks back to fc9ecbeb9 (dir.c: don't flag the index as dirty
> for changes to the untracked cache, 2018-02-05). The motivation of that
> change is that writing the index is expensive, and if the untracked
> cache is the only thing that needs to be written, then it is more
> expensive than the benefit of the cache. However, this also means that
> the untracked cache never gets populated, so the user who enabled it via
> config does not actually get the extension until running 'git
> update-index --untracked-cache' manually or using the environment
> variable.
>
> We have had a version of this change in the microsoft/git fork for a few
> major releases now. It has been working well to get users into a good
> state. Yes, that first index write is slow, but the remaining index
> writes are much faster than they would be without this change.
>
> Signed-off-by: Derrick Stolee <derrickstolee@github.com>
> ---

Will queue.

Thanks.