Status

Current state: Under Discussion

Discussion thread: here 

JIRA: here 

Please keep the discussion on the mailing list rather than commenting on the wiki (wiki discussions get unwieldy fast).

Motivation

Currently, when GlobalStreamThread dies from a fatal error, an InvalidOffsetException will be forwarded to the user which is used to indicate that something wrong had occurred. We have improved upon the durability of GlobalStreamThread previously by wiping all data that had already been processed and rebuilding the store entirely (which was done in KAFKA-6121). However, we should also give the user the option of choosing their reset policy which up to this time, they had no chance of selecting.

There is already a config available "global.consumer.auto.offset.reset" which can be leveraged to reset offsets for global topics. So, no new config needs to be added. But currently, there is no support to override per-topic reset policy for global topics which would require a KIP to change the public interfaces mentioned below.

Public Interfaces

A new reset policy(s) will be added which will allow the user some flexibility in determining the resilience of GlobalStreamThread.  It should also be noted that Topology.addGlobalStore does not allow the user to decide which policy to use. This method will have to be extended. 

public class Topology { 

	// newly added
    public synchronized <K, V> Topology addGlobalStore(final AutoOffsetReset offsetReset,
													   final StoreBuilder<?> storeBuilder,
                                                       final String sourceName,
                                                       final TimestampExtractor timestampExtractor,
                                                       final Deserializer<K> keyDeserializer,
                                                       final Deserializer<V> valueDeserializer,
                                                       final String topic,
                                                       final String processorName,
                                                       final ProcessorSupplier<K, V> stateUpdateSupplier) {
    }
}

Proposed Changes

• Using config- global.consumer.auto.offset.reset to set reset policy for GlobalStreamThread and take actions based on this policy(cleaning up the stores and seekToBeginning/seekToEnd) based on this config as we do based on auto.offset.reset in StreamThread.
• Add the interface mentioned above to allow users to reset per-topic overrides for GlobalTopics.

Compatibility, Deprecation, and Migration Plan

• The current Topology.addGlobalStore method will be extended. We will add a second version of addGlobalStore with extra input parameters while the original method calls the added method with default values. This would not force the user to change their preexisting code in any way.

Rejected Alternatives

• Wipe the store and seekToBeginning and log the error in case of InvalidOffsetException instead of providing a reset policy.