Subject: Re: [PATCH] checkout: don't write merge results into the object database

From: Junio C Hamano <[email-masked]>
Date: Thu, 15 Jun 2017 14:56:03 -0700

René Scharfe <[email-masked]> writes:

>> If it is a concern, I think it could be solved by "unpretending" after
>> our call to checkout_entry completes. That would need a new call in
>> sha1_file.c, but it should be easy to write.
>
> Good point; we'd accumulate fake entries that we'll never need again.

Hopefully we are not pretending to have the same object from two
callsites; this one may knows the merged one no longer needs to be
in core, but some other callsite wanted to pretend a blob with the
same contents is in the object store, what happens to it?  I do not
think we want to refcount ;-)

> The patch should clean them up.
>
> Alternatively we could finally address the NEEDSWORK comment and
> provide a way to checkout a file without faking an index entry..

Yeah, we should not need index entry, and we should not need the
blob object name.

    ... thinks a bit more ...

Having said that, in the longer term, it may be safe to write an
actual object out to the object store.  The convert-to-working-tree
backends currently work only on raw bytes, but it is not inplausible
for some new interfaces to want to pass the object name to the
backend and tell it either togive raw (converted) bytes back, or to
write out the bytes directly to the filesystem, bypassing the main
Git process.  If we "pretend" in this process, not just we accumulate
cruft in-core as Peff points out, we risk giving out an invalid object
name to such external mechanisms.

I do not think it is too bad to leave a handful of temporary blobs
that are written out by "git checkout -m <other-branch>" in the
object store to be GC'ed.