[FLINK-29395][Connector/Kinesis] Handle empty deaggregated records…

[hlteoh37]

…in FanOutRecordPublisher

What is the purpose of the change

The consumer fails when three conditions are met:

1. Kinesis EFO record publisher uses an AT_TIMESTAMP starting position.
2. The first record batch is not empty.
3. The deaggregated record batch is empty.

This can happen when the user writes aggregated records into their Kinesis stream whilst specifying the explicitHashKey for every single user record. When resharding occurs, there is a possibility that records within the same aggregated batch fall into two different shards, since they have different explicit hash keys. When this happens, the deaggregated records are dropped. (We need to do this in Kinesis Consumer so we do not process duplicate records. See awslabs/kinesis-aggregation#11)

If all deaggregated records are dropped, the consumer receives an empty deaggregated record batch even though the record batch is not empty.

Brief change log

This is fixed by returning the AT_TIMESTAMP starting position when receiving an AT_TIMESTAMP sentinel sequence number.

Verifying this change

• Unit tests

Does this pull request potentially affect one of the following parts:

• Dependencies (does it add or upgrade a dependency): no
• The public API, i.e., is any changed class annotated with @Public(Evolving): no
• The serializers: no
• The runtime per-record code paths (performance sensitive): no
• Anything that affects deployment or recovery: JobManager (and its components), Checkpointing, Kubernetes/Yarn, ZooKeeper: no
• The S3 file system connector: no

Documentation

• Does this pull request introduce a new feature? no
• If yes, how is the feature documented? not applicable

[flinkbot]

CI report:

• 74a6b1c Azure: SUCCESS

Bot commands

The @flinkbot bot supports the following commands:

• @flinkbot run azure re-run the last Azure build

[dannycranmer]

Thanks for the deep dive! The solution LGTM, just one comment on the unit test

[dannycranmer]

Thanks @hlteoh37m LGTM