DataStax Java Driver 4.x Backpressure Changes Impact Connection Pool Saturation

Goal

Determine how the backpressure semantics introduced in DataStax Java Driver 4.x alter the detection and handling of connection‑pool exhaustion compared with the 3.x series.

Constraints and Uncertainty

Configuration keys, metric names, and default pool sizes differ between the two major driver versions. Server‑side overload, hot partitions, and GC pauses can produce symptoms that look like client‑side pool saturation, making it difficult to isolate the root cause without version‑specific observability.

Which metric names should be monitored to detect saturation in each driver version? What are the default pool sizes and timeout defaults for 3.x versus 4.x? What configuration changes are required when migrating to 4.x to preserve the previous backpressure behavior?