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7/23/2026
Debugging a Legacy Java Pipeline: Connection Pool Exhaustion and Compounding Failures

Debugging a Legacy Java Pipeline: Connection Pool Exhaustion and Compounding Failures

Original: Jerry Ran Out of Numbers But Drank All the Punch

Short summary

An engaging narrative about debugging 'Jerry,' a legacy Java data-pipeline application that started failing under performance-test workloads. The story traces through DB2 connection pool exhaustion, zombie JDBC threads, and a series of seemingly unrelated timeouts and deadlocks that resisted every targeted fix. The post illustrates how legacy systems accumulate multiple overlapping problems so that every reasonable theory is partially correct yet none is the complete answer.

  • •Legacy Java app 'Jerry' fails under load with DB2 connection pool exhaustion and zombie threads
  • •Multiple overlapping bugs make every theory partially right but none the complete fix
  • •Story highlights the difficulty of diagnosing compounding issues in legacy enterprise systems

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