Leader Lease
Objective
To introduce the Leader Lease Read feature into Ratis to enhance read capabilities and address existing limitations.
Current Implementation Limitations
- Leader Bypass Read: Offers improved latency and throughput but is constrained to the leader and may produce inconsistent results.
- Server Linearizable Read (ReadIndex): Allows clients to read from any server, ensuring linearizability but suffers from suboptimal latency (20-30% throughput drop compared to bypass read).
Reasons for Proposed Feature (Leader Lease Read)
- Validated by other communities (e.g., Sofa-Jraft), resulting in a 15% improvement in throughput performance.
- Addresses the demand for low-latency read capabilities from downstream dependents like IoTDB for time-series queries.
Configuration
To enable and configure Leader Lease, the following properties can be set in RaftServerConfigKeys:
| Property | Description | Type | Default |
|---|---|---|---|
raft.server.read.leader.lease.enabled | Whether to enable lease in linearizable read-only requests. | boolean | false |
raft.server.read.leader.lease.timeout.ratio | Maximum timeout ratio of leader lease. | double (ranging from 0.0 to 1.0) | 0.9 |
Related Issues and References
- Previous community discussions: RATIS-1864, RATIS-1273 and https://github.com/apache/ratis/pull/383
- Quantitative results: https://www.sofastack.tech/en/projects/sofa-jraft/jraft-user-guide/ (Section 5. Linearizable read)