Developer Recounts Months-Long Battle With a Legacy Java App's Cascading Bugs

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A software developer has shared a detailed account of debugging a legacy Java application, nicknamed Jerry, originally built on a Java 8 stack to move data reliably into a database. Over time, the app grew unwieldy through incomplete rewrites and staff turnover, leaving it poorly suited for increased workloads. Performance testing exposed a cascade of failures, beginning with an exhausted HikariCP connection pool and zombie threads holding onto database resources. Each apparent fix would seem to resolve the issue, only for timeouts and deadlocks to resurface weeks later under different test conditions. The story was submitted as part of DEV Community's Summer Bug Smash writing challenge, sponsored by Sentry.

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