[KAFKA-9186] Kafka Connect floods logs with probably bogus error messages from DelegatingClassLoader

• Type: Bug
• Status: Resolved
• Priority: Minor
• Resolution: Fixed
• Affects Version/s: 2.3.1
• Fix Version/s: 2.5.0, 3.0.0
• Component/s: connect
• Assignee: Chia-Ping Tsai
• Reporter: Piotr Szczepanik
• Reviewer: Jason Gustafson
• Created: 14/Nov/19 12:19
• Updated: 08/Mar/21 17:50
• Resolved: 08/Mar/21 17:50

Description

After upgrading Kafka Connect from 2.3.0 to 2.3.1 we discovered a lot of recurring ERROR messages in Connect's logs.

Plugin class loader for connector: 'com.google.pubsub.kafka.sink.CloudPubSubSinkConnector' was not found. Returning: org.apache.kafka.connect.runtime.isolation.DelegatingClassLoader@58f437b0
logger: org.apache.kafka.connect.runtime.isolation.DelegatingClassLoader

Kafka Connect continues processing the topics as it should be.

We are not using plugin classloader isolation feature by not specifying plugin.path property because we were seeing classloading deadlocks similar to ones described in KAFKA-7421

Maybe the level of this message should be lowered?