Subject: Re: [PATCH 1/5] upload-pack: look up "want" lines via commit-graph

From: Patrick Steinhardt <[email-masked]>
Date: Tue, 1 Mar 2022 09:43:18 +0100

On Wed, Feb 23, 2022 at 09:13:53AM -0500, Derrick Stolee wrote:
> On 2/23/2022 7:35 AM, Patrick Steinhardt wrote:
> 
> > The following benchmark is executed in a repository with a huge number
> > of references. It uses cached request from git-fetch(1) as input and
> > contains about 876,000 "want" lines:
> > 
> >     Benchmark 1: git-upload-pack (HEAD~)
> >       Time (mean ± σ):      7.113 s ±  0.028 s    [User: 6.900 s, System: 0.662 s]
> >       Range (min … max):    7.072 s …  7.168 s    10 runs
> > 
> >     Benchmark 2: git-upload-pack (HEAD)
> >       Time (mean ± σ):      6.622 s ±  0.061 s    [User: 6.452 s, System: 0.650 s]
> >       Range (min … max):    6.535 s …  6.727 s    10 runs
> > 
> >     Summary
> >       'git-upload-pack (HEAD)' ran
> >         1.07 ± 0.01 times faster than 'git-upload-pack (HEAD~)'
> 
> Nice!
> 
> > -		o = parse_object(the_repository, &oid);
> > +		commit = lookup_commit_in_graph(the_repository, &oid);
> > +		if (commit)
> > +			o = &commit->object;
> > +		else
> > +			o = parse_object(the_repository, &oid);
> > +
> 
> This is a neat trick. I see that we've also done this trick in
> revision.c:get_reference(). Perhaps it is worth creating a helper,
> maybe named parse_probably_commit()?

That might be a good idea, thanks. I'll have a look at what the end
result would look like.

Patrick

> >  		if (!o) {
> >  			packet_writer_error(writer,
> >  					    "upload-pack: not our ref %s",
> > @@ -1434,7 +1440,7 @@ static int parse_want_ref(struct packet_writer *writer, const char *line,
> >  	if (skip_prefix(line, "want-ref ", &refname_nons)) {
> >  		struct object_id oid;
> >  		struct string_list_item *item;
> > -		struct object *o;
> > +		struct object *o = NULL;
> >  		struct strbuf refname = STRBUF_INIT;
> >  
> >  		strbuf_addf(&refname, "%s%s", get_git_namespace(), refname_nons);
> > @@ -1448,7 +1454,15 @@ static int parse_want_ref(struct packet_writer *writer, const char *line,
> >  		item = string_list_append(wanted_refs, refname_nons);
> >  		item->util = oiddup(&oid);
> >  
> > -		o = parse_object_or_die(&oid, refname_nons);
> > +		if (!starts_with(refname_nons, "refs/tags/")) {
> > +			struct commit *commit = lookup_commit_in_graph(the_repository, &oid);
> > +			if (commit)
> > +				o = &commit->object;
> > +		}
> > +
> > +		if (!o)
> > +			o = parse_object_or_die(&oid, refname_nons);
> > +
> 
> Even here, we _could_ use a parse_probably_commit() helper
> inside the if (!starts_with(...)) block, even though we would
> still need the if (!o) check later.
> 
> Thanks,
> -Stolee