20.5.1.3 Using Group Replication Group Write Consensus

This section explains how to inspect and configure the maximum number of consensus instances at any time for a group. This maximum is referred to as the event horizon for a group, and is the maximum number of consensus instances that the group can execute in parallel. This enables you to fine tune the performance of your Group Replication deployment. For example, the default value of 10 is suitable for a group running on a LAN, but for groups operating over a slower network such as a WAN, increase this number to improve performance.

Inspecting a Group's Write Concurrency

Use the group_replication_get_write_concurrency() function to inspect a group's event horizon value at runtime by issuing:

SELECT group_replication_get_write_concurrency();

Configuring a Group's Write Concurrency

Use the group_replication_set_write_concurrency() function to set the maximum number of consensus instances that the system can execute in parallel by issuing:

SELECT group_replication_set_write_concurrency(instances);

where instances is the new maximum number of consensus instances. The GROUP_REPLICATION_ADMIN privilege is required to use this function.