In a similar fashion as a previous commit, teach `upload-pack` to avoid
enumerating hidden references where possible.
Note, however, that there are certain cases where cannot avoid
enumerating even hidden references, in particular when either of:
- `uploadpack.allowTipSHA1InWant`, or
- `uploadpack.allowReachableSHA1InWant`
are set, corresponding to `ALLOW_TIP_SHA1` and `ALLOW_REACHABLE_SHA1`,
respectively.
When either of these bits are set, upload-pack's `is_our_ref()` function
needs to consider the `HIDDEN_REF` bit of the referent's object flags.
So we must visit all references, including the hidden ones, in order to
mark their referents with the `HIDDEN_REF` bit.
When neither `ALLOW_TIP_SHA1` nor `ALLOW_REACHABLE_SHA1` are set, the
`is_our_ref()` function considers only the `OUR_REF` bit, and not the
`HIDDEN_REF` one. `OUR_REF` is applied via `mark_our_ref()`, and only
to objects at the tips of non-hidden references, so we do not need to
visit hidden references in this case.
When neither of those bits are set, `upload-pack` can potentially avoid
enumerating a large number of references. In the same example as a
previous commit (linux.git with one hidden reference per commit,
"refs/pull/N"):
$ printf 0000 >in
$ hyperfine --warmup=1 \
'git -c transfer.hideRefs=refs/pull upload-pack . <in' \
'git.compile -c transfer.hideRefs=refs/pull -c uploadpack.allowTipSHA1InWant upload-pack . <in' \
'git.compile -c transfer.hideRefs=refs/pull upload-pack . <in'
Benchmark 1: git -c transfer.hideRefs=refs/pull upload-pack . <in
Time (mean ± σ): 406.9 ms ± 1.1 ms [User: 357.3 ms, System: 49.5 ms]
Range (min … max): 405.7 ms … 409.2 ms 10 runs
Benchmark 2: git.compile -c transfer.hideRefs=refs/pull -c uploadpack.allowTipSHA1InWant upload-pack . <in
Time (mean ± σ): 406.5 ms ± 1.3 ms [User: 356.5 ms, System: 49.9 ms]
Range (min … max): 404.6 ms … 408.8 ms 10 runs
Benchmark 3: git.compile -c transfer.hideRefs=refs/pull upload-pack . <in
Time (mean ± σ): 4.7 ms ± 0.2 ms [User: 0.7 ms, System: 3.9 ms]
Range (min … max): 4.3 ms … 6.1 ms 472 runs
Summary
'git.compile -c transfer.hideRefs=refs/pull upload-pack . <in' ran
86.62 ± 4.33 times faster than 'git.compile -c transfer.hideRefs=refs/pull -c uploadpack.allowTipSHA1InWant upload-pack . <in'
86.70 ± 4.33 times faster than 'git -c transfer.hideRefs=refs/pull upload-pack . <in'
As above, we must visit every reference when
uploadPack.allowTipSHA1InWant is set. But when it is unset, we can visit
far fewer references.
Signed-off-by: Taylor Blau <me@xxxxxxxxxxxx>
---
upload-pack.c | 33 +++++++++++++++++++++++++++------
1 file changed, 27 insertions(+), 6 deletions(-)
diff --git a/upload-pack.c b/upload-pack.c
index 99d216938c..366a101d8d 100644
--- a/upload-pack.c
+++ b/upload-pack.c
@@ -602,11 +602,32 @@ static int get_common_commits(struct upload_pack_data *data,
}
}
+static int allow_hidden_refs(enum allow_uor allow_uor)
+{
+ return allow_uor & (ALLOW_TIP_SHA1 | ALLOW_REACHABLE_SHA1);
+}
+
+static void for_each_namespaced_ref_1(each_ref_fn fn,
+ struct upload_pack_data *data)
+{
+ /*
+ * If `data->allow_uor` allows fetching hidden refs, we need to
+ * mark all references (including hidden ones), to check in
+ * `is_our_ref()` below.
+ *
+ * Otherwise, we only care about whether each reference's object
+ * has the OUR_REF bit set or not, so do not need to visit
+ * hidden references.
+ */
+ if (allow_hidden_refs(data->allow_uor))
+ for_each_namespaced_ref(NULL, fn, data);
+ else
+ for_each_namespaced_ref(data->hidden_refs.v, fn, data);
+}
+
static int is_our_ref(struct object *o, enum allow_uor allow_uor)
{
- int allow_hidden_ref = (allow_uor &
- (ALLOW_TIP_SHA1 | ALLOW_REACHABLE_SHA1));
- return o->flags & ((allow_hidden_ref ? HIDDEN_REF : 0) | OUR_REF);
+ return o->flags & ((allow_hidden_refs(allow_uor) ? HIDDEN_REF : 0) | OUR_REF);
}
/*
@@ -855,7 +876,7 @@ static void deepen(struct upload_pack_data *data, int depth)
* marked with OUR_REF.
*/
head_ref_namespaced(check_ref, data);
- for_each_namespaced_ref(NULL, check_ref, data);
+ for_each_namespaced_ref_1(check_ref, data);
get_reachable_list(data, &reachable_shallows);
result = get_shallow_commits(&reachable_shallows,
@@ -1386,7 +1407,7 @@ void upload_pack(const int advertise_refs, const int stateless_rpc,
if (advertise_refs)
data.no_done = 1;
head_ref_namespaced(send_ref, &data);
- for_each_namespaced_ref(NULL, send_ref, &data);
+ for_each_namespaced_ref_1(send_ref, &data);
if (!data.sent_capabilities) {
const char *refname = "capabilities^{}";
write_v0_ref(&data, refname, refname, null_oid());
@@ -1400,7 +1421,7 @@ void upload_pack(const int advertise_refs, const int stateless_rpc,
packet_flush(1);
} else {
head_ref_namespaced(check_ref, &data);
- for_each_namespaced_ref(NULL, check_ref, &data);
+ for_each_namespaced_ref_1(check_ref, &data);
}
if (!advertise_refs) {
--
2.41.0.16.g26cd413590
