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• there are no more messages available
  • The ConsumerOffsetChecker will show that the log offset of the partitions being consumed does not change on the broker
• the next message available is larger than the maximum fetch size you have specified
  • One possibility of a stalled consumer is that the fetch size in the consumer is smaller than the largest message in the broker. You can use the DumpLogSegments tool to figure out the largest message size and set fetch.size in the consumer config accordingly.
• your client code simply stops pulling messages from the iterator (the blocking queue will fill up).
  • One of the typical causes is that the application code that consumes messages somehow died and therefore killed the consumer thread. We recommend using a try/catch clause to log all Throwable in the consumer logic.

Why messages are delayed in my consumer?

This could be a general throughput issue. If so, you can use more consumer streams (may need to increase # partitions) or make the consumption logic more efficient.

Another potential issue is when multiple topics are consumed in the same consumer connector. Internally, we have an in-memory queue for each topic, which feed the consumer iterators. We have a single fetcher thread per broker that issues multi-fetch requests for all topics. The fetcher thread iterates the fetched data and tries to put the data for different topics into its own in-memory queue. If one of the consumer is slow, eventually its corresponding in-memory queue will be full. As a result, the fetcher thread will block on putting data into that queue. Until that queue has more space, no data will be put into the queue for other topics. Therefore, those other topics, even if they have less volume, their consumption will be delayed because of that. To address this issue, either making sure that all consumers can keep up, or using separate consumer connectors for different topics.

Brokers

How many topics can I have?

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