[FLINK-7282] Credit-based Network Flow Control

• Type: New Feature
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Component/s: Runtime / Network
• External issue URL: https://docs.google.com/document/d/1chTOuOqe0sBsjldA_r-wXYeSIhU2zRGpUaTaik7QZ84
• Assignee: Zhijiang
• Reporter: Zhijiang
• Created: 27/Jul/17 10:57
• Updated: 13/Oct/20 08:13
• Resolved: 13/Oct/20 08:13

Description

This is a part of work for network stack improvements proposed in StephanEwen 's FLIP

Backpressure currently happens very naturally through the TCP network connections and the bounded buffering capacity. The downsides are :

• All channels multiplexed into the same TCP connection stall together, as soon as one channel has backpressure.
• Under backpressure, connections can not transport checkpoint barriers.

This flink-managed flow control is similar to the window-based advertisement mechanism in TCP. The basic approaches are the following:

• Each RemoteInputChannel has fixed exclusive buffers as initial credits, and SingleInputGate has a fixed buffer pool for managing floating buffers for all RemoteInputChannels.
• RemoteInputChannel as receiver notifies the current available credits to the sender side.
• Senders must never send buffers without credit, that means all the buffers sent must be accepted by receivers so no buffers accumulated on the network wire.
• Senders also send the current size of backlog that indicates how many buffers are available on the sender side. The receivers use this information to decide how to request floating buffers from the fixed buffer pool.

To avoid immediate commits affecting master branch, it will be implemented into a separate feature branch.

Sub-Tasks

• Create a fix size (non rebalancing) buffer pool type for the floating buffers: Closed
• Manage exclusive buffers in RemoteInputChannel: Closed
• Add credit field in PartitionRequest message: Closed
• Define the BufferListener interface to replace EventListener in BufferProvider: Closed
• Implement Netty receiver incoming pipeline for credit-based: Closed
• Implement Netty receiver outgoing pipeline for credit-based: Closed
• Implement sender backlog logic for credit-based: Closed
• Implement Netty sender incoming pipeline for credit-based: Closed
• Add the switch for keeping both the old mode and the new credit-based mode: Closed
• Stop assigning floating buffers for blocked input channels in exactly-once mode: Closed
• Implement CheckpointBarrierHandler not to spill data for exactly-once based on credit-based flow control: Closed
• The tag of waiting for floating buffers in RemoteInputChannel should be updated properly: Closed
• Adapt BackPressureStatsTracker to work with credit-based flow control: Closed
• Make credit-based floating buffers optional: Closed
• Lower the minimum number of buffers for incoming channels to 1: Closed
• Make buffer count per InputGate always #channels*buffersPerChannel + ExclusiveBuffers: Closed
• Initial credit should be configured in a separate parameter: Closed
• Avoid recursion stack overflow during releasing SingleInputGate: Closed
• Introduce another greedy mechanism for distributing floating buffers: Closed
• Fix the calculation of backlog in PipelinedSubpartition: Closed
• Construct special test/benchmark to verify the backlog effect: Closed
• Remove non credit based network code: Closed
• Remove the setting of netty channel watermark in NettyServer: Closed
• Solve the potential deadlock problem when reducing exclusive buffers to zero: Closed