Kafka: a read_committed consumer stalls behind one open transaction

Transactional consumers read up to the Last Stable Offset, not the high watermark. A single transaction left open blocks delivery of every record written after it - on that partition, for every consumer group.

• Kafka: linger.ms=0 does not mean every record is sent alone
• Kafka: an eager rebalance stops the entire consumer group
• Kafka: log compaction never removes the last record for a key, including a tombstone
• Kafka: consumer lag on one partition is skew, not a scaling problem
• Kafka: a non-idempotent producer reorders on retry
• Kafka: adding partitions breaks key ordering permanently

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Published 2026-08-25

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