[RATIS-1557] Support linearizable read from followers (Read Index)

• Type: New Feature
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 2.5.0
• Component/s: Linearizable Read
• Labels: gsoc2022 mentor
• Assignee: Song Ziyang
• Reporter: Xinyu Tan
• Created: 21/Mar/22 13:56
• Updated: 04/Aug/23 18:36
• Resolved: 04/Aug/23 18:36

Description

Raft algorithm not only allows linearizable read through Read Index or Lease Read, but also allows linearizable read on the follower nodes, which can increase the read throughput linearly with the number of nodes. Algorithm specific processes can refer to Raft thesis in section 6.4

Our project, Apache IoTDB, is trying to build our high availability module using Ratis. We want Ratis to support linearizable follower read so that we can mask the concept of replicas for upper layers, that is, reading the latest data at any node.

In our survey, sofa-jraft, etcd, tikv-rs and other famous consensus algorithms libraries have supported linearizable follower read. As the only consensus algorithm library under the Apache Foundation, we expect Ratis to support this feature as well, and I'm happy to participate in further discussions and development.

Issue Links

• relates to: RATIS-1262 Support linearizable read
• relates to: RATIS-1864 Support leader lease
• links to: GitHub Pull Request #700

Sub-Tasks

• Record call id for board casting a heartbeat: Resolved
• Trigger to send a heartbeat immediately: Resolved
• Add heartbeat broadcast mechanism for leader readIndex: Resolved
• Support leader linearizable read-only requests: Resolved
• Add new Server RPC: readIndex: Resolved
• Move HeartbeatListeners to LeaderStateImpl: Resolved
• Support linearizable read in AsyncApi: Resolved
• Retry linearizable read when leader steps down: Resolved
• Add linearizable read in Counter example: Resolved
• Support client use linearizable read per request: Resolved
• Fix readIndexHeartbeat using incorrct index handle onAppendEntriesReply method: Resolved
• Fix NPE in ReadIndexHeartbeats: Resolved
• HeartbeatAck use in-correct callId as minCallId: Resolved
• Handle exception of readIndexAsync in gRPC readIndex impl: Resolved