Re: What's cooking in git.git (Sep 2021, #08; Mon, 27)

[Neeraj Singh <nksingh85@gmail.com>]

On Fri, Oct 1, 2021 at 10:02 AM Junio C Hamano <gitster@pobox.com> wrote:
>
> Elijah Newren <newren@gmail.com> writes:
>
> > Said another way, I don't think anything should be writing a critical
> > file that needs to be durable when we're in the middle of a
> > "read-only" process like git-log.  The only things written should be
> > temporary stuff, like the automatic remerge calculation from
> > merge-ort, the textconv cache optimization stuff, or perhaps future
> > gitattributes transformation caching.  All that stuff can safely be
> > blown away at the completion of each merge.
>
> The textconv cache can be populated/written during "git log -p" into
> the object store to persist.  With or without "--remerge-diff", we
> can make design decision to either
>
>  - use temporary object store to discard everything we create at the
>    end in one-go, or
>
>  - write them into the object store to let later gc to handle the
>    crufts.
>
> The former will disable persistent write access to the cache.  It
> still allows accesses the cached data during the same process,
> though.  We so far deemed that textconv cache, when the user enables
> it, is valuable enough to make persistent.  Perhaps remerge-diff's
> tentative merge result may fall into the same category?  Some folks
> may want to cache, others may not.
>
> If we were to use the same notes-cache mechanism, we record the tree
> object (perhaps the object name) as the cached value for the merge
> commit in question.  Hopefully most of the merges are clean merges,
> and "caching" the results of the recreation of the merge would cost
> almost nothing.  We need objects to record the fact that "this merge
> has cached result" in the notes-cache, but the tree object that
> represents the cached result is already in the history the merge
> belongs to.
>

Elijah,
To Junio's point, I'm also curious about why it's so important to
aggressively purge the
mechanical merge cache that you want to do it after each diff
operation rather than once
at the end.