James Cheng created KAFKA-3410:
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Summary: Unclean leader election and "Halting because log
truncation is not allowed"
Key: KAFKA-3410
URL: https://issues.apache.org/jira/browse/KAFKA-3410
Project: Kafka
Issue Type: Bug
Reporter: James Cheng
I ran into a scenario where one of my brokers would continually shutdown, with
the error message:
[2016-02-25 00:29:39,236] FATAL [ReplicaFetcherThread-0-1], Halting because log
truncation is not allowed for topic test, Current leader 1's latest offset 0 is
less than replica 2's latest offset 151 (kafka.server.ReplicaFetcherThread)
I managed to reproduce it with the following scenario:
1. Start broker1, with unclean.leader.election.enable=false
2. Start broker2, with unclean.leader.election.enable=false
3. Create topic, single partition, with replication-factor 2.
4. Write data to the topic.
5. At this point, both brokers are in the ISR. Broker1 is the partition leader.
6. Ctrl-Z on broker2. (Simulates a GC pause or a slow network) Broker2 gets
dropped out of ISR. Broker1 is still the leader. I can still write data to the
partition.
7. Shutdown Broker1. Hard or controlled, doesn't matter.
8. rm -rf the log directory of broker1. (This simulates a disk replacement or
full hardware replacement)
9. Resume broker2. It attempts to connect to broker1, but doesn't succeed
because broker1 is down. At this point, the partition is offline. Can't write
to it.
10. Resume broker1. Broker1 resumes leadership of the topic. Broker2 attempts
to join ISR, and immediately halts with the error message:
[2016-02-25 00:29:39,236] FATAL [ReplicaFetcherThread-0-1], Halting because log
truncation is not allowed for topic test, Current leader 1's latest offset 0 is
less than replica 2's latest offset 151 (kafka.server.ReplicaFetcherThread)
I am able to recover by setting unclean.leader.election.enable=true on my
brokers.
I'm trying to understand a couple things:
* In step 10, why is broker1 allowed to resume leadership even though it has no
data?
* In step 10, why is it necessary to stop the entire broker due to one
partition that is in this state? Wouldn't it be possible for the broker to
continue to serve traffic for all the other topics, and just mark this one as
unavailable?
* Would it make sense to allow an operator to manually specify which broker
they want to become the new master? This would give me more control over how
much data loss I am willing to handle. In this case, I would want broker2 to
become the new master. Or, is that possible and I just don't know how to do it?
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