Subject: Re: [PATCH v2 1/1] repack: avoid loosening promisor objects in partial clones

From: Junio C Hamano <[email-masked]>
Date: Mon, 19 Apr 2021 16:09:03 -0700

Rafael Silva <[email-masked]> writes:

> When `git repack -A -d` is run in a partial clone, `pack-objects`
> is invoked twice: once to repack all promisor objects, and once to
> repack all non-promisor objects. The latter `pack-objects` invocation
> is with --exclude-promisor-objects and --unpack-unreachable, which
> loosens all unused objects. Unfortunately, this includes promisor
> objects.
>
> Because the -d argument to `git repack` subsequently deletes all loose
> objects also in packs, these just-loosened promisor objects will be
> immediately deleted. However, this extra disk churn is unnecessary in
> the first place.  For example, a newly-clone partial repo that filters

"in a newly-cloned partial repo", I'd think.

> For testing, we need to validate whether any object was loosened.
> However, the "evidence" (loosened objects) is deleted during the
> process which prevents us from inspecting the object directory.
> Instead, let's teach `pack-objects` to count loosened objects and
> emit via trace2 thus allowing inspecting the debug events after the
> process is finished. This new event is used on the added regression
> test.

Nicely designed.

> +	uint32_t loosened_objects_nr = 0;
>  	struct object_id oid;
>  
>  	for (p = get_all_packs(the_repository); p; p = p->next) {
> @@ -3492,11 +3493,16 @@ static void loosen_unused_packed_objects(void)
>  			nth_packed_object_id(&oid, p, i);
>  			if (!packlist_find(&to_pack, &oid) &&
>  			    !has_sha1_pack_kept_or_nonlocal(&oid) &&
> -			    !loosened_object_can_be_discarded(&oid, p->mtime))
> +			    !loosened_object_can_be_discarded(&oid, p->mtime)) {
>  				if (force_object_loose(&oid, p->mtime))
>  					die(_("unable to force loose object"));
> +				loosened_objects_nr++;
> +			}
>  		}
>  	}
> +
> +	trace2_data_intmax("pack-objects", the_repository,
> +			   "loosen_unused_packed_objects/loosened", loosened_objects_nr);
>  }

OK, so this is just the "stats".

> diff --git a/builtin/repack.c b/builtin/repack.c
> index 2847fdfbab..5f9bc74adc 100644
> --- a/builtin/repack.c
> +++ b/builtin/repack.c
> @@ -20,7 +20,7 @@ static int delta_base_offset = 1;
>  static int pack_kept_objects = -1;
>  static int write_bitmaps = -1;
>  static int use_delta_islands;
> -static char *packdir, *packtmp;
> +static char *packdir, *packtmp_name, *packtmp;
>  
>  static const char *const git_repack_usage[] = {
>  	N_("git repack [<options>]"),
> @@ -530,7 +530,8 @@ int cmd_repack(int argc, const char **argv, const char *prefix)
>  	}
>  
>  	packdir = mkpathdup("%s/pack", get_object_directory());
> -	packtmp = mkpathdup("%s/.tmp-%d-pack", packdir, (int)getpid());
> +	packtmp_name = xstrfmt(".tmp-%d-pack", (int)getpid());
> +	packtmp = mkpathdup("%s/%s", packdir, packtmp_name);

Just a mental note, but we should move away from ".tmp-$$" that is a
remnant from the days back when this was a shell script, and use the
tempfile.h API (#leftoverbits).  Such a change must not be part of
this topic, of course.

Thanks.  Will queue and see what others say.