graphql-engine/server/benchmarks

This is our v2 benchmark suite, which gets run in CI. It makes use of graphql-bench internally (which in turn uses the K6 load testing tool)

Here is an overview of this directory:

benchmark_sets/*

Each sub-directory here contains a different schema and accompanying latency benchmarks (see below for adding your own). Each benchmark set runs in parallel on CI. See benchmark_sets/chinook/ for reference.

In a benchmark set directory, the existence of an empty file named one of the following have the following effects:

• SKIP_CI: don't run the benchmark in CI at all
• SKIP_PR_REPORT: don't post the regression results directly in the PR comment body (useful if the results are noisy for now)

benchmark_sets//adhoc_operations/

Each script here (if present) defines a non-graphql operation to be benchmarked. These are run in sequence after the graphql-bench -powered queries defined in the config.query.yaml files.

These are suitable for e.g. metadata queries or more complex interactions with the server, where you don't care about concurrent requests and where the work is CPU-bound (because in the future reporting will highlight stable metrics like CPU mutator time and allocations).

Because of the overhead of timing things in bash you probably don't want to rely on the wallclock latency numbers for queries that are faster than 100 ms. These numbers may also be noisier since we're running single-threaded and so taking fewer samples.

bench.sh

This script runs a particular benchmark set against a particular hasura docker image or, if omitted, the hasura running on port 8181. e.g. to run the chinook benchmarks:

$ ./bench.sh chinook hasura/graphql-engine:v2.0.1

Only fairly recent (as of this writing) builds of hasura are supported.

Be aware benchmarks are tuned for our beefy CI machines, and some may perform poorly and give useless output on a laptop with few cores.

fabfile.py

This is the core of the CI functionality. It's possible to run this locally but you'll need credentials (see .circleci/config.yaml). In general this can be ignored.

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Interpreting benchmark results

• bytes_alloc_per_req should be very stable but of course doesn't measure, e.g. whether we're generating efficient SQL

• min latency is often stable, especially when we have many (>5,000) samples; a regression here may mean a change to the code is influencing performance ...or it might indicate the test run was unstable and should be taken with a grain of salt, or retried

• ...but long tail latencies are very important; the 90th percentile may be a better target to optimize for than the median (50th percentile)

• ...but keep in mind that longtail latencies are by definition noisey: the 99.9th percentile may represent only a handful of samples. Therefore be cautious when drawing inferences from a comparison of tail latencies between versions.

• If Memory Residency has changed:

  • live_bytes is just the total size of heap objects after GC, and is quite deterministic; mem_in_use is closer to what users experience in their nice graphs

  • does the regression show up in huge_schema? If not maybe a function was turned into a CAF. Small, constant memory usage increases are probably not a big deal

    The following is good background for mem_in_use vs. live_bytes, and why we might care:

    https://well-typed.com/blog/2021/01/fragmentation-deeper-look/ https://well-typed.com/blog/2021/03/memory-return/

• If optimizing or tuning the output/compression codepath:

  • chinook.*_small_result and simple_query_* queries are average wrt response body size (according to cloud data)
  • ...and chinook.full_introspection is ~P95

Adding a new benchmark and reviewing

You'll create a new directory under benchmark_sets/, and in general can follow the pattern from chinook. The process looks like:

• export_metadata to create your replace_metadata.json using stable hasura if possible, so that you can compare performance against older versions of hasura (e.g. chinook and huge_schema use v2 of metadata)

• check major_gcs from /dev/rts_stats before and after a test run, ensuring the benchmark ran for long enough to perform at least a few major GCs.

• play with benchmark duration, so that results are repeatable but take no longer than necessary (see also above)

• if you're interested in latency, be sure you haven't requested a rate too close to the throughput limit; experiment locally to find an appropriate upper bounds for load.

• set preAllocatedVUs juar high enough so that K6 doesn't have to allocate VUs during test, and you see no dropped_iterations reported

• look for ✓ no error in body in K6 output to make sure your query is correct (assuming you're not benchmarking error handling)

• document the purpose of the benchmark. e.g. "large response bodies at high throughput", or "complex joins with conditions on a table with a lot of data, ensuring we're generating an efficient query"; give context so your fellow developers have a sense of what a regression means

Make sure the benchmark set takes less than 20 minutes, otherwise it will be killed. You can always split benchmarks up into two different sets to be run in parallel.

If a benchmark set is not fairly stable, or you're not sure if it is, add an empty file named SKIP_PR_REPORT in the benchmark set's directory; this will prevent display of regression numbers in the PR comment body, but will still run and record the benchmarks.

For code reviewers: help double-check the above, in particular look for errors in K6 output. Take a look at the detailed GUI report, make sure if using constant-arrival-rate that the query can keep up with load.