Subject: Re: [PATCH v3 2/5] object-file.c: handle undetermined oid in write_loose_object()

From: Junio C Hamano <[email-masked]>
Date: Mon, 29 Nov 2021 12:44:43 -0800

Derrick Stolee <[email-masked]> writes:

> My first reaction is to not write into .git/objects/ directly, but
> instead make a .git/objects/tmp/ directory and write within that
> directory. The idea is to prevent leaving stale files in the
> .git/objects/ directory if the process terminates strangely (say,
> a power outage or segfault).

Even if we know the name of the object we are writing beforehand, I
do not think it is a good idea to open-write-close the final object
file.  The approach we already use everywhere is to write into a
tmpfile/lockfile and rename it to the final name 

object-file.c::write_loose_object() uses create_tmpfile() to prepare
a temporary file whose name begins with "tmp_obj_", so that "gc" can
recognize stale ones and remove them.

> If this was an interesting idea to pursue, it does leave a question:
> should we clean up the tmp/ directory when it is empty? That would
> require adding a check in finalize_object_file() that is probably
> best left unchecked (the lstat() would add a cost per loose object
> write that is probably too costly). I would rather leave an empty
> tmp/ directory than add that cost per loose object write.

I am not sure why we want a new tmp/ directory.