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  1. Kafka
  2. KAFKA-1756

never allow the replica fetch size to be less than the max message size

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    Details

    • Type: Bug
    • Status: Resolved
    • Priority: Major
    • Resolution: Not A Problem
    • Affects Version/s: 0.8.1.1, 0.8.2.0
    • Fix Version/s: None
    • Component/s: None
    • Labels:
      None

      Description

      There exists a very hazardous scenario where if the max.message.bytes is greather than the replica.fetch.max.bytes the message will never replicate. This will bring the ISR down to 1 (eventually/quickly once replica.lag.max.messages is reached). If during this window the leader itself goes out of the ISR then the new leader will commit the last offset it replicated. This is also bad for sync producers with -1 ack because they will all block (heard affect caused upstream) in this scenario too.

      The fix here is two fold

      1) when setting max.message.bytes using kafka-topics we must check first each and every broker (which will need some thought about how todo this because of the topiccommand zk notification) that max.message.bytes <= replica.fetch.max.bytes and if it is NOT then DO NOT create the topic

      2) if you change this in server.properties then the broker should not start if max.message.bytes > replica.fetch.max.bytes

      This does beg the question/issue some about centralizing certain/some/all configurations so that inconsistencies do not occur (where broker 1 has max.message.bytes > replica.fetch.max.bytes but broker 2 max.message.bytes <= replica.fetch.max.bytes because of error in properties). I do not want to conflate this ticket but I think it is worth mentioning/bringing up here as it is a good example where it could make sense.

      I set this as BLOCKER for 0.8.2-beta because we did so much work to enable consistency vs availability and 0 data loss this corner case should be part of 0.8.2-final

      Also, I could go one step further (though I would not consider this part as a blocker for 0.8.2 but interested to what other folks think) about a consumer replica fetch size so that if the message max is increased messages will no longer be consumed (since the consumer fetch max would be < max.message.bytes

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            • Assignee:
              Unassigned
              Reporter:
              joestein Joe Stein
            • Votes:
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              Dates

              • Created:
                Updated:
                Resolved: