[IGNITE-19120] Raft client should get leader metadata along while getting leader itself

• Type: Improvement
• Status: Patch Available
• Priority: Major
• Resolution: Unresolved
• Labels: ignite-3
• Assignee: Vladislav Pyatkov
• Reporter: Denis Chudov
• Reviewer: Alexander Lapin
• Created: 24/Mar/23 12:35
• Updated: 12/Jul/23 08:07

Description

Motivation

This ticket is about TopologyAwareRaftGroupService which can subscribe on leader change. Necessary metadata is last log index and last applied index in leader's storage. 

This will allow to remove readIndex requests on acceptance of a lease on leaseholder candidate. As we know that no write commands in replication group can happen in absence of leaseholder, this means that leaseholder should just catch up leader's last log index received with leader metadata to make sure that its local storage is up-to-date. Applied index can be not reliable as leader may be being recovered and applied index maybe in progress of catch-up with log index, but it might be useful to know applied index on leaseholder candidate to justify time of waiting for actual storage state.

Definition of done

readIndex call is removed from Replica#waitForActualState.

Issue Links

• relates to: IGNITE-19833 Function to understand that the replication group majority is lost
• links to: GitHub Pull Request #2255