Re: [PATCH] unpack-trees: allow missing CE_SKIP_WORKTREE objs
- From
Ben Peart <peartben@gmail.com>
- Date
- Oct 9, 2018, 14:48 UTC
- Message-ID
- <7ac4ea1d-596d-cffd-337f-bf1879d982e1@gmail.com>
- In-Reply-To
- <20181008214816.42856-1-jonathantanmy@google.com>
On 10/8/2018 5:48 PM, Jonathan Tan wrote:
Show 19 quoted lines
> Whenever a sparse checkout occurs, the existence of all blobs in the > index is verified, whether or not they are included or excluded by the > .git/info/sparse-checkout specification. This degrades performance, > significantly in the case of a partial clone, because a lazy fetch > occurs whenever the existence of a missing blob is checked. > > At the point of invoking cache_tree_update() in unpack_trees(), > CE_SKIP_WORKTREE is already set on all excluded blobs > (mark_new_skip_worktree() is called twice to set CE_NEW_SKIP_WORKTREE, > then apply_sparse_checkout() is called which copies over > CE_NEW_SKIP_WORKTREE to CE_SKIP_WORKTREE). cache_tree_update() can use > this information to know which blobs are excluded, and thus skip the > checking of these. > > Because cache_tree_update() is used from multiple places, this new > behavior is guarded by a new flag WRITE_TREE_SKIP_WORKTREE_MISSING_OK. > Implement this new flag, and teach unpack_trees() to invoke > cache_tree_update() with this new flag. >
I wonder if preventing the download of all missing blobs should be limited to only the checkout command. When you looked at the other places that call cache_tree_update(), does it make sense that they trigger the download of all the missing blobs? For example, I suspect you would not want them all downloaded just to do a merge-recursive.
In full disclosure, we implemented this a couple of years ago [1] for GVFS and opted to do the logic a little differently. We found that we didn't want to trigger the download of all missing blobs in cache_tree_update() for _any_ command that was executing in a partially cloned repo. This is safe because if any individual blob is actually needed, it will get downloaded "on demand" already.
[1] https://github.com/Microsoft/git/commit/ec865500d98
Show 102 quoted lines
> Signed-off-by: Jonathan Tan <jonathantanmy@google.com>
> ---
> cache-tree.c | 6 +++++-
> cache-tree.h | 4 ++++
> t/t1090-sparse-checkout-scope.sh | 33 ++++++++++++++++++++++++++++++++
> unpack-trees.c | 1 +
> 4 files changed, 43 insertions(+), 1 deletion(-)
>
> diff --git a/cache-tree.c b/cache-tree.c
> index 5ce51468f0..340caf2d34 100644
> --- a/cache-tree.c
> +++ b/cache-tree.c
> @@ -246,6 +246,8 @@ static int update_one(struct cache_tree *it,
> int missing_ok = flags & WRITE_TREE_MISSING_OK;
> int dryrun = flags & WRITE_TREE_DRY_RUN;
> int repair = flags & WRITE_TREE_REPAIR;
> + int skip_worktree_missing_ok =
> + flags & WRITE_TREE_SKIP_WORKTREE_MISSING_OK;
> int to_invalidate = 0;
> int i;
>
> @@ -356,7 +358,9 @@ static int update_one(struct cache_tree *it,
> }
>
> if (is_null_oid(oid) ||
> - (mode != S_IFGITLINK && !missing_ok && !has_object_file(oid))) {
> + (mode != S_IFGITLINK && !missing_ok &&
> + !(skip_worktree_missing_ok && ce_skip_worktree(ce)) &&
> + !has_object_file(oid))) {
> strbuf_release(&buffer);
> if (expected_missing)
> return -1;
> diff --git a/cache-tree.h b/cache-tree.h
> index 0ab6784ffe..655d487619 100644
> --- a/cache-tree.h
> +++ b/cache-tree.h
> @@ -40,6 +40,10 @@ void cache_tree_verify(struct index_state *);
> #define WRITE_TREE_DRY_RUN 4
> #define WRITE_TREE_SILENT 8
> #define WRITE_TREE_REPAIR 16
> +/*
> + * Do not check for the presence of cache entry objects with CE_SKIP_WORKTREE.
> + */
> +#define WRITE_TREE_SKIP_WORKTREE_MISSING_OK 32
>
> /* error return codes */
> #define WRITE_TREE_UNREADABLE_INDEX (-1)
> diff --git a/t/t1090-sparse-checkout-scope.sh b/t/t1090-sparse-checkout-scope.sh
> index 25d7c700f6..090b7fc3d3 100755
> --- a/t/t1090-sparse-checkout-scope.sh
> +++ b/t/t1090-sparse-checkout-scope.sh
> @@ -63,4 +63,37 @@ test_expect_success 'return to full checkout of master' '
> test "$(cat b)" = "modified"
> '
>
> +test_expect_success 'in partial clone, sparse checkout only fetches needed blobs' '
> + test_create_repo server &&
> + git clone "file://$(pwd)/server" client &&
> +
> + test_config -C server uploadpack.allowfilter 1 &&
> + test_config -C server uploadpack.allowanysha1inwant 1 &&
> + echo a >server/a &&
> + echo bb >server/b &&
> + mkdir server/c &&
> + echo ccc >server/c/c &&
> + git -C server add a b c/c &&
> + git -C server commit -m message &&
> +
> + test_config -C client core.sparsecheckout 1 &&
> + test_config -C client extensions.partialclone origin &&
> + echo "!/*" >client/.git/info/sparse-checkout &&
> + echo "/a" >>client/.git/info/sparse-checkout &&
> + git -C client fetch --filter=blob:none origin &&
> + git -C client checkout FETCH_HEAD &&
> +
> + git -C client rev-list HEAD \
> + --quiet --objects --missing=print >unsorted_actual &&
> + (
> + printf "?" &&
> + git hash-object server/b &&
> + printf "?" &&
> + git hash-object server/c/c
> + ) >unsorted_expect &&
> + sort unsorted_actual >actual &&
> + sort unsorted_expect >expect &&
> + test_cmp expect actual
> +'
> +
> test_done
> diff --git a/unpack-trees.c b/unpack-trees.c
> index 51bfac6aa0..39e0e7a6c7 100644
> --- a/unpack-trees.c
> +++ b/unpack-trees.c
> @@ -1635,6 +1635,7 @@ int unpack_trees(unsigned len, struct tree_desc *t, struct unpack_trees_options
> o->result.cache_tree = cache_tree();
> if (!cache_tree_fully_valid(o->result.cache_tree))
> cache_tree_update(&o->result,
> + WRITE_TREE_SKIP_WORKTREE_MISSING_OK |
> WRITE_TREE_SILENT |
> WRITE_TREE_REPAIR);
> }
>