[KAFKA-6924] Making state store queryable on replicas

• Type: New Feature
• Status: Resolved
• Priority: Major
• Resolution: Duplicate
• Component/s: streams
• Assignee: Unassigned
• Reporter: Navinder Brar
• Created: 21/May/18 05:41
• Updated: 22/May/18 15:16
• Resolved: 22/May/18 15:16

Description

State store in Kafka streams are currently only queryable when StreamTask is in RUNNING state. The idea is to make it queryable even for StandbyTasks to decrease the downtime if client is not able to fetch data from Active machine.

Suppose the coordinator is not able to connect to machine which had active partition due to some reason. So, rather than failing that request we could serve request from replica which could be on some other machine. Although state on replica might be little behind the active but it could still be beneficial in some cases to serve request from replica than failing the request.

It's very important improvement as it could simply improve the availability of microservices developed using kafka streams.

I am working on a patch for this change. Any feedback or comments are welcome.

Also, I have gone thorugh https://issues.apache.org/jira/browse/KAFKA-6031, has this been implemented?