[jira] [Created] (KAFKA-9866) Do not attempt to elect preferred leader replicas which are outside ISR

["Stanislav Kozlovski (Jira)" <ji...@apache.org>]

Stanislav Kozlovski created KAFKA-9866:
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             Summary: Do not attempt to elect preferred leader replicas which are outside ISR
                 Key: KAFKA-9866
                 URL: https://issues.apache.org/jira/browse/KAFKA-9866
             Project: Kafka
          Issue Type: Improvement
            Reporter: Stanislav Kozlovski


The controller automatically triggers a preferred leader election every N minutes. It tries to elect all preferred leaders of partitions without doing some basic checks like whether the leader is in sync.

This leads to a multitude of errors which cause confusion:
{code:java}
April 14th 2020, 17:01:11.015	[Controller id=0] Partition TOPIC-9 failed to complete preferred replica leader election to 1. Leader is still 0{code}
{code:java}
April 14th 2020, 17:01:11.002	[Controller id=0] Error completing replica leader election (PREFERRED) for partition TOPIC-9
kafka.common.StateChangeFailedException: Failed to elect leader for partition TOPIC-9 under strategy PreferredReplicaPartitionLeaderElectionStrategy {code}
It would be better if the Controller filtered out some of these elections, not attempt them at all and maybe log an aggregate INFO-level log



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