[RFC PATCH] fetch-pack: lazy fetch using tree:0
- From
- Jonathan Tan <jonathantanmy@google.com>
- Date
- Mar 19, 2020, 17:44 UTC
- Message-ID
- <20200319174439.230969-1-jonathantanmy@google.com>
Support for partial clones with filtered trees was added in bc5975d24f ("list-objects-filter: implement filter tree:0", 2018-10-07), but whenever a lazy fetch of a tree is done, besides the tree itself, some other objects that it references are also fetched.
The "blob:none" filter was added to lazy fetches in 4c7f9567ea ("fetch-pack: exclude blobs when lazy-fetching trees", 2018-10-04) to restrict blobs from being fetched, but it didn't restrict trees. ("tree:0", which would restrict all trees as well, wasn't added then because "tree:0" was itself new and may not have been supported by Git servers, as you can see from the dates of the commits.)
Now that "tree:0" has been supported in Git for a while, teach lazy fetches to use "tree:0" instead of "blob:none".
(An alternative to doing this is to teach Git a new filter that only returns exactly the objects requested, no more - but "tree:0" already does that for us for now, hence this patch. If we were to support filtering of commits in partial clones later, I think that specifying a depth will work to restrict the commits returned, so we won't need an additional filter anyway.) --- This looks like a good change to me - in particular, it makes Git align with the (in my opinion, reasonable) mental model that when we lazily fetch something, we only fetch that thing. Some issues that I can think about:
- Some hosts like GitHub support some partial clone filters, but not "tree:0". - I haven't figured out the performance implications yet. If we want a tree, I think that we typically will want some of its subtrees, but not all.
Any thoughts? --- fetch-pack.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/fetch-pack.c b/fetch-pack.c index 1734a573b0..655ec5d4a3 100644 --- a/fetch-pack.c +++ b/fetch-pack.c @@ -1747,14 +1747,14 @@ struct ref *fetch_pack(struct fetch_pack_args *args, /* * The protocol does not support requesting that only the * wanted objects be sent, so approximate this by setting a - * "blob:none" filter if no filter is already set. This works - * for all object types: note that wanted blobs will still be + * "tree:0" filter if no filter is already set. This works + * for all object types: note that wanted blobs and trees will still be * sent because they are directly specified as a "want". * * NEEDSWORK: Add an option in the protocol to request that * only the wanted objects be sent, and implement it. */ - parse_list_objects_filter(&args->filter_options, "blob:none"); + parse_list_objects_filter(&args->filter_options, "tree:0"); } if (version != protocol_v2 && !ref) {
-- 2.25.1.696.g5e7596f4ac-goog