Okada Haruki

## Summary - Fix a typo in the comment about `TLCFcnElementVariableValue` parsing * `|->` should be `:>`

I think it is useful to add extension fallback feature to SbtTwirl. It will work as follows. - If you have set `formatFallback: SettingKey[Option[String]]` and template's extension does not match...

- Currently, Decaton's SubPartitioner uses murmur2 hash of the key to determine the subpartition to ensure per-key processing ordering guarantee. - However, sometimes we want to use round-robin strategy even...

Support cooperative rebalancing protocol

1

- Kafka 2.4.0 introduces `cooperative rebalancing protocol`, which mitigates the stop-the-world effect upon rebalancing * https://cwiki.apache.org/confluence/display/KAFKA/KIP-429%3A+Kafka+Consumer+Incremental+Rebalance+Protocol - Users can opt-in cooperative rebalancing by specifying `CooperativeStickyAssignor` in `partition.assignment.strategy` config or implementing...

- In Kafka, it's common to use some entity's identifier (e.g. user-id) to ensure task processing ordering per entity. - At the same time, this tends to cause "hot-spot" key...

Provide BatchingProcessor as a built-in processor

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- Task batching is a common-pattern that many Decaton users often implement by their own * i.e. Batching several tasks of type `T` to `List` and process them at once....

Adopt poll(Duration) fixes #118

1

## Summary - Currently, Decaton uses `KafkaConsumer#poll(long)` which is deprecated and could be removed in future Kafka release

## Summary - Currently, rebalance-listener could block indefinitely in below scenario: * Let's say: - There are 3 partitions (0,1,2) - 3 instances (X,Y,Z) - partition-0 is assigned to X...

## Summary - Currently, Decaton uses `KafkaConsumer#poll(long)` which could block indefinitely and already marked as deprecated * https://github.com/line/decaton/blob/v3.0.1/processor/src/main/java/com/linecorp/decaton/processor/runtime/internal/ConsumeManager.java#L165 - We should migrate to `poll(Duration)` overload

## Summary - Currently, ProcessorSubscription's state transitions to RUNNING at the end of rebalance listener (onPartitionsAssigned) - So, offset-reset could be happen in later `poll()` after transitioned to RUNNING -...