Add benchmarks for Updater
Our update-ref wrapper doesn't have currently any benchmarks. This MR adds benchmarks for both updates and deletions. Deletions are also benchmarked with refs loose and packed. Creations are not benchmarked separately as the operation is the same as an update.
The performance of update-ref is important for &8903 and &8911 as all reference updates need to be serialized and applied through the log. The benchmarks here give us an idea of what sort of reference change throughput we can achieve with log application.
Running the benchmark on my laptop gives us few points:
- Reference update throughput caps at 50 updates/s. This means we currently can't achieve high enough throughput to match our peak load mutator rates. The results do not get better with increased transaction sizes.
- Reference deletion throughput with packed refs matches the update throughput when transaction size is 1. The performance improves dramatically when transaction size is increased.
Deletions respond well to bigger transaction sizes which gives us some leeway in optimizing our log processing by batching multiple transactions into a single write. This is likely due to packed-refs file having to be rewritten only once for a deletion. The reference updates end up in loose files regardless of the transaction size which makes batching transactions quite ineffective. This will likely get better with future reference file formats in Git as they'd allow for batching multiple transactions into a single write.
Benchmark Results
goos: darwin goarch: amd64 pkg: gitlab.com/gitlab-org/gitaly/v15/internal/git/updateref cpu: Intel(R) Core(TM) i9-9880H CPU @ 2.30GHz BenchmarkUpdater BenchmarkUpdater/update BenchmarkUpdater/update/transaction_size:_1 BenchmarkUpdater/update/transaction_size:_1-16 52 20710401 ns/op 48.32 reference_updates/s 269 B/op 12 allocs/op BenchmarkUpdater/update/transaction_size:_10 BenchmarkUpdater/update/transaction_size:_10-16 6 199396022 ns/op 50.18 reference_updates/s 2881 B/op 57 allocs/op BenchmarkUpdater/update/transaction_size:_100 BenchmarkUpdater/update/transaction_size:_100-16 1 2002251276 ns/op 49.96 reference_updates/s 18808 B/op 450 allocs/op BenchmarkUpdater/delete BenchmarkUpdater/delete/reference_count_100/references_packed_false/transaction_size_1 BenchmarkUpdater/delete/reference_count_100/references_packed_false/transaction_size_1-16 1393 941592 ns/op 1063 reference_deletions/s 206 B/op 11 allocs/op BenchmarkUpdater/delete/reference_count_100/references_packed_true/transaction_size_1 BenchmarkUpdater/delete/reference_count_100/references_packed_true/transaction_size_1-16 57 21183865 ns/op 47.23 reference_deletions/s 278 B/op 11 allocs/op BenchmarkUpdater/delete/reference_count_100/references_packed_false/transaction_size_10 BenchmarkUpdater/delete/reference_count_100/references_packed_false/transaction_size_10-16 306 4080364 ns/op 2452 reference_deletions/s 702 B/op 38 allocs/op BenchmarkUpdater/delete/reference_count_100/references_packed_true/transaction_size_10 BenchmarkUpdater/delete/reference_count_100/references_packed_true/transaction_size_10-16 44 24515611 ns/op 408.1 reference_deletions/s 819 B/op 39 allocs/op BenchmarkUpdater/delete/reference_count_100/references_packed_false/transaction_size_100 BenchmarkUpdater/delete/reference_count_100/references_packed_false/transaction_size_100-16 48 24458077 ns/op 4090 reference_deletions/s 5800 B/op 308 allocs/op BenchmarkUpdater/delete/reference_count_100/references_packed_true/transaction_size_100 BenchmarkUpdater/delete/reference_count_100/references_packed_true/transaction_size_100-16 31 37074623 ns/op 2699 reference_deletions/s 5885 B/op 309 allocs/op PASS ok gitlab.com/gitlab-org/gitaly/v15/internal/git/updateref 365.684s