Implement ReducePartition

[wsry]

Motivation

As described in the document, ReducePartition is a good supplement of the current MapPartition. It has several good features, for example, it can benefit streaming and hybrid shuffle (mixed streaming and batch) and it is good for performance for some scenarios.

Changes

It is big change including many aspects, including shuffle API enhancement (Flink side), ShuffleMaster change, shuffle write/read change, network protocol change, storage change, fault tolerance change and so on. We need to Implement it step by step.

Tasks

• SortBuffer supports reading data from the specified channel index #40

Test

• UT test.
• E2E test.
• Stability test.
• Test manually on a cluster.

[qiunanx]

@TanYuxin-tyx Is this feature already implemented ?