Limits of Ruby Connection Pool Timeout for Detecting Intermittent Exhaustion

Goal: Identify a reliable way to detect when a Ruby connection pool is approaching exhaustion before threads experience timeout‑induced latency spikes.

Constraints: The connection_pool gem only raises a Timeout::Error after the per‑checkout timeout expires and does not emit warnings or metrics; developers must either poll pool.available_size or rescue exceptions, which can add overhead and may miss short‑lived exhaustion events. Behavior differs between gem versions and when the pool is wrapped by ActiveRecord’s database.yml settings.

Which monitoring strategy provides the earliest indication of exhaustion with minimal performance impact, and how should the timeout value be tuned relative to expected request latency to avoid false positives?