Tag: JVM Java Mastery

All the articles with the tag "JVM Java Mastery".

• Decoding HikariCP Pool Exhaustion via JVM Thread Dump — What TIMED_WAITING (parked) Really Means

  3 May, 2026

  When the pool exhaustion alert fires, staring at application code yields nothing. The thread dump from jstack is the real evidence — every worker thread is frozen in HikariCP at TIMED_WAITING (parked). I walk through the JVM Thread State machine, LockSupport.parkNanos, the ConcurrentBag and SynchronousQueue mechanics, and how the transaction-with-external-call pool-exhaustion measurement [measured] (timeout 5s = 100% pass / 1s = 16.7%) maps line-by-line to the dump — diagnosing pool exhaustion from a single dump in production.

• When equals/hashCode Goes Wrong: A Duplicate Payment Incident Post-Mortem

  9 Jan, 2026

  A deep dive into how forgetting to override hashCode() while implementing equals() caused duplicate payments. Includes Kafka TopicPartition analysis, HashMap internals, and code review checklists.