AlwaysOn Policies for Operational Issues with AlwaysOn Availability Groups (SQL Server)
The AlwaysOn Availability Groups health model evaluates a set of predefined policy based management (PBM) policies. You can use theses for viewing the health of an availability group and its availability replicas and databases in SQL Server 2016.
In this Topic:
- AlwaysOn predefined policies
A set of built-in policies that allow a database administrator to check an availability group and its availability replicas and databases for compliance with the states that are defined by the AlwaysOn policies.
- AlwaysOn Availability Groups
A high-availability and disaster-recovery solution that provides an enterprise-level alternative to database mirroring.
- availability group
A container for a discrete set of user databases, known as availability databases, that fail over together.
- availability replica
An instantiation of an availability group that is hosted by a specific instance of SQL Server and that maintains a local copy of each availability database that belongs to the availability group. Two types of availability replicas exist: a single primary replica and one to four secondary replicas. The server instances that host the availability replicas for a given availability group must reside on different nodes of a single Windows Server Failover Clustering (WSFC) cluster.
- availability database
A database that belongs to an availability group. For each availability database, the availability group maintains a single read-write copy (the primary database) and one to four read-only copies (secondary databases).
- AlwaysOn Dashboard
A SQL Server Management Studio dashboard that provides an at-a-glance view of the health of an availability group. For more information, see AlwaysOn Dashboard, later in this topic.
The following table summarizes the predefined policies.
WSFC Cluster State
Instance of SQL Server
Availability Group Online State
Availability Group Automatic Failover Readiness
Availability Replicas Data Synchronization State
Synchronous Replicas Data Synchronization State
Availability Replicas Role State
Availability Replicas Connection State
Availability Replica Role State
Availability Replica Connection State
Availability Replica Join State
Availability Replica Data Synchronization State
Availability Database Suspension State
Availability Database Join State
Availability Database Data Synchronization State
*For AlwaysOn policies, the category names are used as IDs. Changing the name of an AlwaysOn category would break its health-evaluation functionality. Therefore, do not modify the names of AlwaysOn categories.
The AlwaysOn Dashboard gives you an at-a-glance view of the health of an availability group. The AlwaysOn Dashboard includes the following features:
Enables you to easily display details about a given availability group, its availability replicas, and its databases.
Displays visual indications of key states to help database administrators make quick operational decisions.
Provides launch points for troubleshooting scenarios.
For a given operational issue, populates the Policy Evaluation Result dialog box with information about specific AlwaysOn health policy violations and with links to remediation help.
Provides an health extended event viewer to show previous events for AlwaysOn-specific issues.
If failing over the availability group is a possible remediation for an issue, provides a launch point for the links Fail Over Availability Group Wizard. This wizard takes a database administrator through the manual failover process.
Extending the AlwaysOn Availability Groups health model is simply a matter of creating your own user-defined policies and putting them into certain categories based on the type of object that you are monitoring. After you a alter few settings, the AlwaysOn dashboard will automatically evaluate your own user-defined policies, as well as the AlwaysOn predefined policies.
A user-defined policy can use any of the available PBM facets, including those used by the AlwaysOn predefined policies (see Predefined Policies and Issues, earlier in this topic). The Server facet provides the following properties for monitoring AlwaysOn Availability Groups health: (IsHadrEnabled and HadrManagerStatus). The Server facet also provides properties the following policies for monitoring the WSFC cluster configuration: ClusterQuorumType, and ClusterQuorumState.
For more information, see The AlwaysOn Health Model Part 2 -- Extending the Health Model (a SQL Server AlwaysOn Team blog).