Context

Clean up and import the latency load testing package to enable validation of driver behavior under load, supporting DRIVERS-3320 (client backpressure testing): https://github.com/prestonvasquez/dev/tree/main/mongo-go-driver/v1/metrics/latency

The framework generates load by spawning workers until a target latency threshold is reached, then runs user-defined experiments while capturing metrics. This simulates real-world conditions where the driver is under pressure:

1. Preloads a test collection with random documents
2. Spawns workers that execute FindOne operations, measuring latency
3. Dynamically adds workers until average latency exceeds target threshold
4. Once under load, triggers user-defined experiment functions
5. Collects and reports metrics at completion

Currently the following metrics are captures:

• Connection pool: closed count, close reasons/errors, ready durations, pending read success/failure
• Commands: started/succeeded/failed counts
• Operations: count, timeout errors, average/median duration

Definition of done

• Import the latency package and update for V2 compatibility.
• Create an evergreen task that runs the workload. If possible, Use send-perf-data for the metrics so that this data can be compared over time.
• Determine which metrics should be supported.
• Determine an architecture that can be extended for different workloads.

Pitfalls

The framework tests a narrow workload pattern (concurrent FindOne on non-existent keys). Results may not generalize to workloads with mixed operations, large documents, aggregations, or write-heavy patterns. This ticket should be for implementing an extendable baseline and not to create comprehensive coverage.