MySQL Bugs: #90284: Add an acceptor only role to leverage it in single-primary mode

Bug #90284	Add an acceptor only role to leverage it in single-primary mode
Submitted:	3 Apr 2018 1:05	Modified:	3 Apr 2018 14:50
Reporter:	Artem Danilov	Email Updates:
Status:	Verified	Impact on me:	None
Category:	MySQL Server: Group Replication	Severity:	S4 (Feature request)
Version:		OS:	Any
Assigned to:		CPU Architecture:	Any

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Description:
Group replication configured in single-primary mode still reserves slots for all members in the log and requires non-primary nodes to send skip messages to guarantee progress for the primary. This adds visible overhead for latency sensitive applications. 

How to repeat:
Setup group replication with 3 members with 100ms latency between all members. The operations from a single client in the tight loop shows multiple RTs latency but I'd expect it to be close to 1 RT to the closest replica.

Suggested fix:
Single-primary mode should not reserve slots for non-primary members so that primary progress won't be blocked on waiting for skip messages from all members of the group.