Always On in SQL Server 2017 (Read-Scale Feature)
SQL server 2017 has introduced new feature and technology (read-scale availability group) with Always on. Now, Always On availability groups provide high availability, disaster recovery and read-scale balancing.
Read-Scale Availability Group: This architecture provides replicas for read-only workloads but no HA. There is a question why we need this new architecture:
In SQL Server 2016 and before, all availability groups required a cluster and cluster provides a business continuity HADR. SQL Server 2017 introduces read-scale availability groups without a cluster.
This feature is very useful in case if the business needs to keep the resources for mission-critical workloads running on the primary then users can route to readable secondary replicas without using any cluster technology.
CLUSTER_TYPE: There are three different cluster types which are used while creating availability group as below
- WSFCWinows server failover cluster. On Windows, it is the default value for CLUSTER_TYPE.
- EXTERNALA cluster manager that is not Windows server failover cluster – for example, on Linux with Pacemaker.
- NONENo cluster manager. Used for a read-scale availability group.
How to get the details for cluster type used in availability group:
Two new columns: cluster_type and cluster_type_desc
Select name as ‘Availability Groups ’, cluster_type, cluster_type_desc from sys.availability_groups.
Thanks for reading!
Awaiting your valuable responses…