[jira] [Created] (KAFKA-6555) Making state store queryable during restoration

["Ashish Surana (JIRA)" <ji...@apache.org>]

Ashish Surana created KAFKA-6555:
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             Summary: Making state store queryable during restoration
                 Key: KAFKA-6555
                 URL: https://issues.apache.org/jira/browse/KAFKA-6555
             Project: Kafka
          Issue Type: Improvement
          Components: streams
            Reporter: Ashish Surana


State store in Kafka streams are currently only queryable when StreamTask is in RUNNING state. The idea is to make it queryable even in the RESTORATION (PARTITION_ASSIGNED) state as the time spend on restoration can be huge and making the data inaccessible during this time could be downtime not suitable for many applications.

When the active partition goes down then one of the following occurs:
 # One of the standby replica partition gets promoted to active: Replica restores the remaining state from the changelog topic. The time taken for this depends on how much the replica is lagging behind in consuming changelog topic. During this restoration time the state store for that partition is not queryable giving us the downtime for the entire parition. We can make it queryable for the data already present in the state store.
 # When there is no replica or standby task, then active task will be started in one of the existing node. That node has to build the entire state from the changelog topic which can take lot of time depending on how big is the changelog topic, and keeping state store not queryable during this time is the downtime for the parition.

 

It's very important improvement as it could simply improve the availability of microservices developed using kafka streams. Any feedback or comments are welcome.

 

 



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