Re: [PATCH 3/6] object-file: extract logic to approximate object count

> In "builtin/gc.c" we have some logic that checks whether we need to
> repack objects. This is done by counting the number of objects that we
> have and checking whether it exceeds a certain threshold. We don't
> really need an accurate object count though, which is why we only
> open a single object diretcroy shard and then extrapolate from there.

>
> Extract this logic into a new function that is owned by the loose object
> database source. This is done to prepare for a subsequent change, where
> we'll introduce object counting on the object database source level.
>
> Signed-off-by: Patrick Steinhardt <ps@pks.im>
> ---
>  builtin/gc.c  | 37 +++++++++----------------------------
>  object-file.c | 41 +++++++++++++++++++++++++++++++++++++++++
>  object-file.h | 13 +++++++++++++
>  3 files changed, 63 insertions(+), 28 deletions(-)
>
> diff --git a/builtin/gc.c b/builtin/gc.c
> index fb329c2cff..a08c7554cb 100644
> --- a/builtin/gc.c
> +++ b/builtin/gc.c
> @@ -467,37 +467,18 @@ static int rerere_gc_condition(struct gc_config *cfg UNUSED)
>  static int too_many_loose_objects(int limit)
>  {
>  	/*
> -	 * Quickly check if a "gc" is needed, by estimating how
> -	 * many loose objects there are.  Because SHA-1 is evenly
> -	 * distributed, we can check only one and get a reasonable
> -	 * estimate.
> +	 * This is weird, but stems from legacy behaviour: the GC auto
> +	 * threshold was always essentially interpreted as if it was rounded up
> +	 * to the next multiple 256 of, so we retain this behaviour for now.
>  	 */
> -	DIR *dir;
> -	struct dirent *ent;
> -	int auto_threshold;
> -	int num_loose = 0;
> -	int needed = 0;
> -	const unsigned hexsz_loose = the_hash_algo->hexsz - 2;
> -	char *path;
> -
> -	path = repo_git_path(the_repository, "objects/17");
> -	dir = opendir(path);
> -	free(path);
> -	if (!dir)
> +	int auto_threshold = DIV_ROUND_UP(limit, 256) * 256;
> +	unsigned long loose_count;
> +
> +	if (odb_source_loose_approximate_object_count(the_repository->objects->sources,
> +						      &loose_count) < 0)
>  		return 0;
>  
> -	auto_threshold = DIV_ROUND_UP(limit, 256);
> -	while ((ent = readdir(dir)) != NULL) {
> -		if (strspn(ent->d_name, "0123456789abcdef") != hexsz_loose ||
> -		    ent->d_name[hexsz_loose] != '\0')
> -			continue;
> -		if (++num_loose > auto_threshold) {
> -			needed = 1;
> -			break;
> -		}
> -	}
> -	closedir(dir);
> -	return needed;
> +	return loose_count > auto_threshold;
>  }
>  
>  static struct packed_git *find_base_packs(struct string_list *packs,
> diff --git a/object-file.c b/object-file.c
> index a3ff7f586c..da67e3c9ff 100644
> --- a/object-file.c
> +++ b/object-file.c
> @@ -1868,6 +1868,47 @@ int odb_source_loose_for_each_object(struct odb_source *source,
>  					     NULL, NULL, &data);
>  }
>  
> +int odb_source_loose_approximate_object_count(struct odb_source *source,
> +					      unsigned long *out)
> +{
> +	const unsigned hexsz = source->odb->repo->hash_algo->hexsz - 2;
> +	unsigned long count = 0;
> +	struct dirent *ent;
> +	char *path = NULL;
> +	DIR *dir = NULL;
> +	int ret;
> +
> +	path = xstrfmt("%s/17", source->path);
> +
> +	dir = opendir(path);
> +	if (!dir) {
> +		if (errno == ENOENT) {
> +			*out = 0;
> +			ret = 0;
> +			goto out;
> +		}
> +
> +		ret = error_errno("cannot open object shard '%s'", path);
> +		goto out;
> +	}
> +
> +	while ((ent = readdir(dir)) != NULL) {
> +		if (strspn(ent->d_name, "0123456789abcdef") != hexsz ||
> +		    ent->d_name[hexsz] != '\0')
> +			continue;
> +		count++;
> +	}
> +
> +	*out = count * 256;