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Update testing section of global-tag-throttling.md

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sfc-gh-tclinkenbeard 2022-11-14 06:07:07 -08:00 committed by Trevor Clinkenbeard
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@ -116,12 +116,12 @@ If an individual zone is unhealthy, it may cause the throttling ratio for storag
### Client Rate Calculation
The smoothed per-client rate for each tag is tracked within `GlobalTagThrottlerImpl::PerTagStatistics`. Once a target rate has been computed, this is passed to `GlobalTagThrotterImpl::PerTagStatistics::updateAndGetPerClientRate` which adjusts the per-client rate. The per-client rate is meant to limit the busiest clients, so that at equilibrium, the per-client rate will remain constant and the sum of throughput from all clients will match the target rate.
## Testing
The `GlobalTagThrottling.toml` test provides a simple end-to-end test using the global tag throttler. Quotas are set using the internal tag quota API in the `GlobalTagThrottling` workload. This is run in parallel with the `ReadWrite` workload, which tags transactions. The number of `transaction_tag_throttled` errors is reported, along with the throughput, which should be roughly predictable based on the quota parameters chosen.
## Simulation Testing
The `ThroughputQuota.toml` test provides a simple end-to-end test using the global tag throttler. Quotas are set using the internal tag quota API in the `ThroughputQuota` workload. This is run with the `Cycle` workload, which randomly tags transactions.
In addition to this end-to-end test, there is a suite of unit tests with the `/GlobalTagThrottler/` prefix. These tests run in a mock environment, with mock storage servers providing simulated storage queue statistics and tag busyness reports. Mock clients simulate workload on these mock storage servers, and get throttling feedback directly from a global tag throttler which is monitoring the mock storage servers.
In each test, the `GlobalTagThrottlerTesting::monitor` function is used to periodically check whether or not a desired equilibrium state has been reached. If the desired state is reached and maintained for a sufficient period of time, the test passes. If the unit test is unable to reach this desired equilibrium state before a timeout, the test will fail. Commonly, the desired state is for the global tag throttler to report a client rate sufficiently close to the desired rate specified as an input to the `GlobalTagThrottlerTesting::rateIsNear` function.
In each unit test, the `GlobalTagThrottlerTesting::monitor` function is used to periodically check whether or not a desired equilibrium state has been reached. If the desired state is reached and maintained for a sufficient period of time, the test passes. If the unit test is unable to reach this desired equilibrium state before a timeout, the test will fail. Commonly, the desired state is for the global tag throttler to report a client rate sufficiently close to the desired rate specified as an input to the `GlobalTagThrottlerTesting::rateIsNear` function.
## Visibility