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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 NetworkException: The Server Disconnected — How to Fix It

Fix org.apache.kafka.common.errors.NetworkException: the server disconnected before a response was received. Root causes, idempotent retries, LB timeouts.

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Kafka: Marking the Coordinator Dead — Causes and Fix

Kafka consumer stuck logging 'Marking the coordinator dead' / 'Group coordinator is unavailable or invalid, will attempt rediscovery'. Here's the real cause and the fix.

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Kafka ListenerNotFoundException: No Matching Listener Fix

Kafka ListenerNotFoundException and 'leader brokers without a matching listener' explained: why the leader lacks the listener, how to reproduce, and the fix.

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Kafka LEADER_NOT_AVAILABLE: Why It Happens and How to Fix It

Kafka LEADER_NOT_AVAILABLE floods your producer logs the moment you write to a fresh topic. Here's the exact cause, the reproduction, and the real fix.

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KafkaStorageException: Disk Error & No Space Left on Device

Fix org.apache.kafka.common.errors.KafkaStorageException and 'No space left on device' broker shutdowns — recovery runbook, retention math, disk sizing.

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Kafka InvalidTxnStateException: Causes and How to Fix It

InvalidTxnStateException means your producer called a transactional API in the wrong state. Here's the state machine, the exact triggers, and the fix.

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Kafka InvalidTopicException: Why It Happens and How to Fix It

Kafka InvalidTopicException — 'Topic name is illegal' from bad characters, 249-char limits, or '.'/'_' collisions. The exact rules, root cause, and the fix.

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Kafka InvalidStateStoreException: State Store May Have Migrated

Fixing InvalidStateStoreException: "the state store may have migrated to another instance" in Kafka Streams — root causes, retry logic, and the right IQ design.

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Kafka InvalidReplicationFactorException: Larger Than Available Brokers

Fix Kafka's InvalidReplicationFactorException — "Replication factor: 3 larger than available brokers: 1" — in Docker and single-broker dev setups fast.

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Kafka InvalidGroupIdException: Fixing the group.id Error

Hitting InvalidGroupIdException: "you must provide a valid group.id"? Why subscribe() and offset commits require a group.id in Kafka, and the exact fix.