Re: [PATCH] packfile: skip decompressing and hashing blobs in add_promisor_object()

> OK, so we are checking the type up front and then skipping
> parse_object() if we can. But there is already some logic inside
> parse_object() for these kinds of optimizations. If we tell it we are
> not interested in checking the hash of the objects, then it knows it can
> skip loading the blob entirely.
> 
> But it can _also_ use that flag for other things, like using the
> commit-graph rather than loading individual commit objects. So doing
> this:
>   
> diff --git a/packfile.c b/packfile.c
> index 9cc11b6dc5..01b992a4e1 100644
> --- a/packfile.c
> +++ b/packfile.c
> @@ -2310,7 +2310,8 @@ static int add_promisor_object(const struct object_id *oid,
>  		we_parsed_object = 0;
>  	} else {
>  		we_parsed_object = 1;
> -		obj = parse_object(pack->repo, oid);
> +		obj = parse_object_with_flags(pack->repo, oid,
> +					      PARSE_OBJECT_SKIP_HASH_CHECK);
>  	}
>  
>  	if (!obj)
> 
> drops my linux.git case down to 49s. It's skipping the blobs (with no
> need for your patch) and loading the commits out of the graph file. Note
> that you may need to "git commit-graph write --reachable" to see the
> effect (I think we do generate graphs by default in git-gc these days,
> but I'm not sure if we do so right after cloning).