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Gopi Gorantala

I'm Gopi — 15+ years in Java, building Kafka and Flink platforms for banks, where one lost event is a financial discrepancy. I write javahandbook.com because the guides I needed didn't exist. Everything here is tested against a real cluster first.

HikariPool-1 - Connection is not available, request timed out after 30000ms: Diagnosing and Fixing Connection Pool Exhaustion in Spring Boot

A production-grade breakdown of the HikariCP Connection is not available timeout in Spring Boot — why it happens under load, how to reproduce it locally, and how to fix and prevent pool exhaustion for good.

Kafka TopicAuthorizationException: Not Authorized to Access Topics — Fix

Hitting TopicAuthorizationException: Not authorized to access topics in Kafka? Here's why ACLs deny you, how principals really resolve, and the exact fix.

Kafka Failed to Acquire Lock on File .lock: How to Fix It

Kafka broker won't start: 'Failed to acquire lock on file .lock ... A Kafka instance in another process is using this directory.' Why it happens and how to fix it.

Consumer Rebalance Storms: Why Your Kafka Consumer Group Never Stabilizes

A deep dive into Kafka consumer rebalance storms — the exact CommitFailedException and JoinGroup log spam that signals it, why max.poll.interval.ms and eager rebalancing are usually to blame, and how to fix it with cooperative sticky assignment and static membership.

LazyInitializationException: could not initialize proxy — no Session — Root Cause and Fix

A deep dive into Spring Boot's LazyInitializationException, why it slips past code review and blows up in production, and how to fix it properly instead of slapping @Transactional on everything.

Kafka InstanceAlreadyExistsException: AppInfo Mbean Fix

Kafka logs 'Error registering AppInfo mbean javax.management.InstanceAlreadyExistsException'. Here's what a duplicate client.id really breaks and how to fix it.

Kafka Timeout Before Position for Partition Could Be Determined

Kafka consumer failing with TimeoutException: Timeout of 60000ms expired before the position for partition could be determined? Here's the fix.

Kafka: Timed out waiting for a node assignment — Fix

Kafka AdminClient and kafka-topics.sh fail with 'Timed out waiting for a node assignment. Call: createTopics'. Here's why it happens and the exact fix.

Kafka Streams LockException: Failed to Lock the State Directory

Kafka Streams throwing LockException: Failed to lock the state directory for task? Here's the exact cause, why it happens, and the fix.

Kafka: Connection Terminated During Authentication — Fix

Kafka AuthenticationException 'terminated during authentication' with its three-reason hint decoded: security.protocol mismatch, TLS/firewall, and mTLS. Repro plus the fix.