Status

Current state: Under discussion

...

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

Motivation

In order for state stores to provide stronger consistency in the future (e.g., RYW consistency) they need to be able to collect record metadata (e.g., offset information).

...

The task of this ticket is to expose recordMetadata via the StateStoreContext. 

Public Interfaces

The following interface will change:

• org.apache.kafka.stream.processor.StateStoreContext - adding method recordMetadata()

Proposed Changes

The code segment below shows the actual code change together with the corresponding JavaDoc:

...

A POC with an example showing how recordMetadata can be used in state stores is given here:  https://github.com/patrickstuedi/kafka/tree/record-metadata2

Compatibility, Deprecation, and Migration Plan

The change of the StateStoreContext interface does not require any changes to any of the implementations of the interface, it merely exposes (recordMetadata) a method that is already implemented in AbstractProcessorContext. Therefore we do not expect any compatibility issues. Moreover, recordMetadata returns an object of type RecordMetadata which is exclusively read-only, thus, protecting Kafka-internal from being tampered by applications. 

Rejected Alternatives

None.