Subject: Re: [PATCH 1/1] commit-graph.c: avoid unnecessary tag dereference when merging

From: Taylor Blau <[email-masked]>
Date: Sat, 21 Mar 2020 18:20:05 -0600

On Sat, Mar 21, 2020 at 08:03:01PM -0400, Derrick Stolee wrote:
> On 3/21/2020 2:50 PM, Junio C Hamano wrote:
> > Do we need to worry about INFO_QUICK and SKIP_FETCH_OBJECT in this
> > codepath, by the way?
>
> I was coming back to this thread to bring up these exact flags for
> consideration. The good news is that in a partial clone with any
> amount of filtering we will still have all reachable commits, which
> are necessary for the commit-graph to make sense. The only ones that
> would fail has_object_file() are ones removed by GC, but they may
> still exist on the remote. So without SKIP_FETCH_OBJECT, we would
> generate a network call even if the server has GC'd to remove the
> commits. This gets particularly bad when the server returns all
> reachable objects from that commit!

That makes sense. Do you think something like this should be applied?

diff --git a/commit-graph.c b/commit-graph.c
index c7cfadc786..0097318798 100644
--- a/commit-graph.c
+++ b/commit-graph.c
@@ -1594,6 +1594,7 @@ static void merge_commit_graph(struct write_commit_graph_context *ctx,
 {
        uint32_t i;
        uint32_t offset = g->num_commits_in_base;
+       int flags = OBJECT_INFO_QUICK | OBJECT_INFO_SKIP_FETCH_OBJECT;

        ALLOC_GROW(ctx->commits.list, ctx->commits.nr + g->num_commits, ctx->commits.alloc);

@@ -1606,7 +1607,7 @@ static void merge_commit_graph(struct write_commit_graph_context *ctx,
                load_oid_from_graph(g, i + offset, &oid);

                /* only add commits if they still exist in the repo */
-               if (repo_has_object_file(ctx->r, &oid)) {
+               if (repo_has_object_file_with_flags(ctx->r, &oid, flags)) {
                        result = lookup_commit(ctx->r, &oid);
                        if (repo_parse_commit(ctx->r, result))
                                result = NULL;

> Thanks,
> -Stolee

Thanks,
Taylor