All the callback functions which write refs in the reftable backend
perform D/F conflict checks via `refs_verify_refname_available()`. But
in reality we perform these D/F conflict checks a second time in the
reftable library via `stack_check_addition()`.
Interestingly, the code in the reftable library is inferior compared to
the generic function:
- It is slower than `refs_verify_refname_available()`, even though
this can probably be optimized.
- It does not provide a proper error message to the caller, and thus
all the user would see is a generic "file/directory conflict"
message.
Disable the D/F conflict checks in the reftable library by setting the
`skip_name_check` write option. This results in a non-negligible speedup
when writing many refs. The following benchmark writes 100k refs in a
single transaction:
Benchmark 1: update-ref: create many refs (HEAD~)
Time (mean ± σ): 3.241 s ± 0.040 s [User: 1.854 s, System: 1.381 s]
Range (min … max): 3.185 s … 3.454 s 100 runs
Benchmark 2: update-ref: create many refs (HEAD)
Time (mean ± σ): 2.878 s ± 0.024 s [User: 1.506 s, System: 1.367 s]
Range (min … max): 2.838 s … 2.960 s 100 runs
Summary
update-ref: create many refs (HEAD~) ran
1.13 ± 0.02 times faster than update-ref: create many refs (HEAD)
Signed-off-by: Patrick Steinhardt <ps@xxxxxx>
---
refs/reftable-backend.c | 5 +++++
1 file changed, 5 insertions(+)
diff --git a/refs/reftable-backend.c b/refs/reftable-backend.c
index 8a54b0d8b2..7515dd3019 100644
--- a/refs/reftable-backend.c
+++ b/refs/reftable-backend.c
@@ -247,6 +247,11 @@ static struct ref_store *reftable_be_init(struct repository *repo,
refs->write_options.block_size = 4096;
refs->write_options.hash_id = repo->hash_algo->format_id;
refs->write_options.default_permissions = calc_shared_perm(0666 & ~mask);
+ /*
+ * We verify names via `refs_verify_refname_available()`, so there is
+ * no need to do the same checks in the reftable library again.
+ */
+ refs->write_options.skip_name_check = 1;
/*
* Set up the main reftable stack that is hosted in GIT_COMMON_DIR.
--
2.44.GIT
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