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

• Type: Improvement
• Status: Resolved
• Priority: Minor
• Resolution: Fixed
• Fix Version/s: 2.6.0
• Assignee: Wang Ge
• Reporter: Stanislav Kozlovski
• Created: 14/Apr/20 19:42
• Updated: 27/Apr/20 22:16
• Resolved: 27/Apr/20 20:51

Description

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:

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

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 

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

Issue Links

• links to: GitHub Pull Request #8524