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From: Junio C Hamano <gitster@pobox.com>
To: Jonathan Tan <jonathantanmy@google.com>
Cc: git@vger.kernel.org
Subject: Re: [PATCH v2 4/7] fetch: only populate existing_refs if needed
Date: Wed, 12 Aug 2020 11:06:14 -0700	[thread overview]
Message-ID: <xmqqk0y37n8p.fsf@gitster.c.googlers.com> (raw)
In-Reply-To: <77bc83e7f2c0a9c95e2ff31aa7a11295bbdf054c.1597184949.git.jonathantanmy@google.com> (Jonathan Tan's message of "Tue, 11 Aug 2020 15:52:19 -0700")

Jonathan Tan <jonathantanmy@google.com> 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.

> 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;
>  }

  reply	other threads:[~2020-08-12 18:06 UTC|newest]

Thread overview: 57+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-24 22:38 [RFC PATCH] Modify fetch-pack to no longer die on error? Jonathan Tan
2020-07-24 23:07 ` Junio C Hamano
2020-07-24 23:11 ` Junio C Hamano
2020-07-25 21:41   ` Jeff King
2020-07-25 23:01     ` Junio C Hamano
2020-07-27 17:11       ` Jeff King
2020-07-28 19:23       ` Jonathan Tan
2020-07-28 20:08         ` Jeff King
2020-07-29 18:53           ` Jonathan Tan
2020-07-29 19:29             ` Jeff King
2020-07-29 19:02           ` Junio C Hamano
2020-07-29 22:55             ` Jonathan Tan
2020-08-05  1:20 ` [RFC PATCH 0/7] Lazy fetch with subprocess Jonathan Tan
2020-08-05  1:20   ` [RFC PATCH 1/7] fetch-pack: allow NULL negotiator->add_tip Jonathan Tan
2020-08-05 19:53     ` Junio C Hamano
2020-08-07 20:53       ` Jonathan Tan
2020-08-05  1:20   ` [RFC PATCH 2/7] fetch-pack: allow NULL negotiator->known_common Jonathan Tan
2020-08-05 20:08     ` Junio C Hamano
2020-08-05 22:11       ` Junio C Hamano
2020-08-07 20:59         ` Jonathan Tan
2020-08-05  1:20   ` [RFC PATCH 3/7] negotiator/null: add null fetch negotiator Jonathan Tan
2020-08-05  1:20   ` [RFC PATCH 4/7] fetch: --stdin Jonathan Tan
2020-08-05 20:33     ` Junio C Hamano
2020-08-07 21:10       ` Jonathan Tan
2020-08-07 21:58         ` Junio C Hamano
2020-08-07 21:10       ` Jonathan Tan
2020-08-05  1:20   ` [RFC PATCH 5/7] fetch: submodule config Jonathan Tan
2020-08-05  1:20   ` [RFC PATCH 6/7] fetch: only populate existing_refs if needed Jonathan Tan
2020-08-05  1:20   ` [RFC PATCH 7/7] promisor-remote: use subprocess to fetch Jonathan Tan
2020-08-11 22:52 ` [PATCH v2 0/7] Lazy fetch with subprocess Jonathan Tan
2020-08-11 22:52   ` [PATCH v2 1/7] negotiator/null: add null fetch negotiator Jonathan Tan
2020-08-12 12:55     ` Derrick Stolee
2020-08-12 16:44       ` Junio C Hamano
2020-08-12 17:29         ` Jonathan Tan
2020-08-11 22:52   ` [PATCH v2 2/7] fetch: allow refspecs specified through stdin Jonathan Tan
2020-08-11 22:52   ` [PATCH v2 3/7] fetch: avoid reading submodule config until needed Jonathan Tan
2020-08-12 17:34     ` Junio C Hamano
2020-08-11 22:52   ` [PATCH v2 4/7] fetch: only populate existing_refs if needed Jonathan Tan
2020-08-12 18:06     ` Junio C Hamano [this message]
2020-08-11 22:52   ` [PATCH v2 5/7] fetch-pack: do not lazy-fetch during ref iteration Jonathan Tan
2020-08-12 18:25     ` Junio C Hamano
2020-08-11 22:52   ` [PATCH v2 6/7] promisor-remote: lazy-fetch objects in subprocess Jonathan Tan
2020-08-12 18:28     ` Junio C Hamano
2020-08-11 22:52   ` [PATCH v2 7/7] fetch-pack: remove no_dependents code Jonathan Tan
2020-08-12 12:51   ` [PATCH v2 0/7] Lazy fetch with subprocess Derrick Stolee
2020-08-18  4:01 ` [PATCH v3 " Jonathan Tan
2020-08-18  4:01   ` [PATCH v3 1/7] negotiator/noop: add noop fetch negotiator Jonathan Tan
2020-08-18  4:01   ` [PATCH v3 2/7] fetch: allow refspecs specified through stdin Jonathan Tan
2020-08-18  4:01   ` [PATCH v3 3/7] fetch: avoid reading submodule config until needed Jonathan Tan
2020-08-18  4:01   ` [PATCH v3 4/7] fetch: only populate existing_refs if needed Jonathan Tan
2020-08-18  4:01   ` [PATCH v3 5/7] fetch-pack: do not lazy-fetch during ref iteration Jonathan Tan
2020-08-18  4:01   ` [PATCH v3 6/7] promisor-remote: lazy-fetch objects in subprocess Jonathan Tan
2020-08-18  4:01   ` [PATCH v3 7/7] fetch-pack: remove no_dependents code Jonathan Tan
2020-08-18 19:56   ` [PATCH v3 0/7] Lazy fetch with subprocess Junio C Hamano
2020-08-18 22:32     ` Junio C Hamano
2020-08-18 23:36       ` [PATCH] fixup! promisor-remote: lazy-fetch objects in subprocess Jonathan Tan
2020-08-18 23:57         ` Junio C Hamano

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