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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.

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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.

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Kafka InitProducerId Timeout: Why It Hangs and the Fix

Kafka producer throws 'Timeout expired after 60000ms while awaiting InitProducerId' and initTransactions() hangs on startup. Here's the real root cause and the fix.

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Kafka InconsistentGroupProtocolException: Cause and Fix

Kafka InconsistentGroupProtocolException: the group member's supported protocols are incompatible. Why it hits mid-upgrade and how to fix the assignor mismatch.

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Kafka InconsistentClusterIdException: Cluster ID Mismatch Fix

Fix kafka.common.InconsistentClusterIdException: Cluster ID doesn't match stored clusterId in meta.properties — the Docker volume cause and the real fix.

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Kafka FETCH_SESSION_ID_NOT_FOUND: Causes and Fix

Kafka logs spamming FETCH_SESSION_ID_NOT_FOUND or INVALID_FETCH_SESSION_EPOCH? Here's what the fetch session cache is doing and how to stop the noise.

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Kafka FencedInstanceIdException: Fix Static Membership Collisions

FencedInstanceIdException means two live consumers share one group.instance.id. Here's why the broker fences the old one, and how to fix it for good.

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Kafka "Failed to construct kafka consumer": Every Cause, Fixed

KafkaException: Failed to construct kafka consumer — how to triage every common cause (deserializer class, classpath, DNS, JAAS, SSL) and fix each one fast.

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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.

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Kafka CorruptRecordException: Record Is Corrupt — Fix It

Kafka CorruptRecordException: Record is corrupt (stored crc != computed crc). Why the CRC check fails, how to recover the partition, and how to stop it recurring.

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Kafka: Consumer Is Not Subscribed to Any Topics — Fix

IllegalStateException: Consumer is not subscribed to any topics or assigned any partitions — why poll() throws it, the subscribe/assign contract, and the fix.