[IOTDB-1118] [Distributed] Limit query log lag in mid consistency level

• Type: Improvement
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Component/s: Core/Cluster
• Labels: pull-request-available
• Assignee: Chao Wang
• Reporter: Tian Jiang
• Created: 21/Jan/21 02:30
• Updated: 25/Aug/21 08:17
• Resolved: 06/Mar/21 10:04

Description

We provide a middle level of read consistency, which is a best-effort strategy, and will try to synchronize with the leader and uses the local data when the synchronization times out. However, the maximum log lag is undefined, which means the node can be arbitrarily far from the leader (missing arbitrarily length of logs) and incurs inconvenience when the user wants to control the data freshness.

To resolve this, a configuration should be provided like `max_read_log_lag`, which only takes effect when the consistency level is set to mid, and queries will fail if the log lag exceeds this configuration after a time out.

Issue Links

• is a child of: IOTDB-68 IoTDB supports distributed version
• links to: GitHub Pull Request #2766