Re: [PATCH v2 4/7] fetch: only populate existing_refs if needed
From: Junio C Hamano <hidden>
Date: 2020-08-12 18:06:26
Jonathan Tan [off-list ref] writes:
When fetching tags, Git only writes tags that do not already exist in the client repository. This necessitates an iteration over all the refs, but fetch performs this iteration even if no tags are fetched.
Hmph, the change itself mechanically makes sense (i.e. if the ref_map has no entry with peer_ref defined, existing_refs hashmap is never looked up, so there is no reason to populate it), but the explanation of log message, especially the part that places strees on tags, does not. Wouldn't a plain vanilla "git fetch" with no argument that uses the remote.origin.fetch populated with standard refspecs to maintain remote-tracking branches use this hash? I think the readers need to be somehow made aware of the fact that the author of this commit message is concentrated primarily on fetch used as a mechanism to grab specific objects, often used by lazy fetch, without touching any remote-tracking refs. Because tag following is on by default (which is a convenient default for the plain vanilla fetches that updates remote-tracking branches), however, such a "these specific objects only" fetch still tries to trigger the auto following of tags, and necessitates "--no-tags" to take advantage of the optimization proposed by this patch. So nothing written in the proposed log message is incorrect per-se, but it is not very friendly to readers without clarivoyance.
quoted hunk
diff --git a/builtin/fetch.c b/builtin/fetch.c index 29db219c68..6460ce3f4e 100644 --- a/builtin/fetch.c +++ b/builtin/fetch.c@@ -449,6 +449,7 @@ static struct ref *get_ref_map(struct remote *remote, struct ref *orefs = NULL, **oref_tail = &orefs; struct hashmap existing_refs; + int existing_refs_populated = 0; if (rs->nr) { struct refspec *fetch_refspec;@@ -542,15 +543,18 @@ static struct ref *get_ref_map(struct remote *remote, ref_map = ref_remove_duplicates(ref_map); - refname_hash_init(&existing_refs); - for_each_ref(add_one_refname, &existing_refs); - for (rm = ref_map; rm; rm = rm->next) { if (rm->peer_ref) { const char *refname = rm->peer_ref->name; struct refname_hash_entry *peer_item; unsigned int hash = strhash(refname); + if (!existing_refs_populated) { + refname_hash_init(&existing_refs); + for_each_ref(add_one_refname, &existing_refs); + existing_refs_populated = 1; + } + peer_item = hashmap_get_entry_from_hash(&existing_refs, hash, refname, struct refname_hash_entry, ent);@@ -560,7 +564,8 @@ static struct ref *get_ref_map(struct remote *remote, } } } - hashmap_free_entries(&existing_refs, struct refname_hash_entry, ent); + if (existing_refs_populated) + hashmap_free_entries(&existing_refs, struct refname_hash_entry, ent); return ref_map; }