Introduction to the availability group dynamic management objects in sql server 2016 _ database high availability content from sql server pro

Availability Groups – a hybrid of SQL Server Database Mirroring and Windows Failover Clustering – are becoming the de-facto standard for implementation of high availability solutions for Microsoft SQL Server. Sql server browser While the learning curve can be steep it’s also a fairly short learning curve. What is ms sql server This article does not purport to discuss the nuances of Availability Groups (AGs) nor the processes for installing and configuring “AG’s” but rather focuses on introducing you to the Dynamic Management Objects (DMOs) useful in assessing the architecture and state of your AGs using the SQL Server Dynamic Management Views.

The Dynamic Management Objects we’ll be reviewing in this article are categorized into two areas: those focused on the server level of granularity and those that drill down into the specific state of databases inside the Availability Groups hosted in your environments.


What is sql server used for Regardless of scope you must be granted VIEW SERVER STATE permissions in order to view results from any of these DMV’s.

These DMVs are consistent across SQL Server versions 2012 through 2016. Sql server grouping SQL Server 2016 introduced two new DMV’s pertaining to the new feature/method of seeding replicas without a backup/restore process:

We are not covering these now but will do so in a future article where I show how to use this functionality to avoid the process of backup and restore to seed a replica – similar to how SQL Azure creates replicas on AG creation already.

We will break these down showing an overview of what each DMV provides in terms of information (columns returned) and some of the questions that each answers individually or with the assistance of other DMVs or System Catalog Views. Sql server services Some of these objects are only good for resolving object ID’s (ag_id, group_id, replica_id, etc.) to a logical name but most serve valid purposes for helping to identify synchronization state, AG health, architecture, configuration, and more. Sql server developer edition You should not feel limited by the graphical user interface offerings (GUI) inside SQL Server Management Studio. Online ms sql server Thanks to the SQL Server Dynamic Management Views you have countless options for building your own monitoring scripts and dashboards for dealing with Availability Groups in your SQL Server environments.

This DMV provides quorum information for each node in a WSFC that is supporting an AG. Sql server 2008 training If the node has quorum it will display quorum information for that node. Server name sql express If there is no quorum no results are returned.

sys.dm_hadr_cluster_members provides information about all the nodes in the clustering ecosystem that builds the foundations for your Availability Groups. Sql server group by month It identifies the server name of each participating node, the type of participant (node or witness), and the state of the participant. Sql server update The columns of primary interest are going to be provided through the following query – not all columns provide value.

This DMV exposes the instance name and WSFC node name for all instances participating in the WSFC. Use of sql server You’ll also see the ag_resource_id assigned to the instance. What is sql database server This allows you to relate a node name and SQL instance name back to any DMV exposing ag_resource_id for rationalizing the ag_resource_id into something meaningful for identification. Sql server 2008 express with advanced services You’ll likely never query this DMV directly, but rather as part of a larger query using it to provide a naming context when otherwise only an ag_resource_id exists.

Additionally, as Microsoft points out in their own documentation, “this dynamic management view is useful for detecting an availability group with multiple availability replicas that are hosted on the same WSFC node, which is an unsupported configuration that could occur after an FCI failover if the availability group is incorrectly configured.”

This DMV exists solely to allow for linking and name resolution should the Availability Group be renamed. Sql server limit Just like logins and users in SQL are associated with a sid that uniquely identifies the entity (rather than the login name or user name identifying the entity) so is the case with the ag_id. For en sql server Likewise as you’ll see in subsequent DMVs later in this article resources and groups that comprise the AG ecosystem – while having a name property that can be changed – also have an underlying ID value that cannot be changed and will always be used to maintain relationships between the various objects and levels of granularity in the AG. What is meant by sql server This DMV is used throughout joins that afford relationships between many of the DMVs discussed in this article. Sql server compact It will be rare that you would query this DMV directly but common to use it as an intermediate join between two or more DMVs. Install sql server express The resource_id and group_id map back to WSFC resources and resource groups.

It should be noted – because it’s confusing – that ag_id is associated with the identity of the Availability Group whereas the ag_group_id identifies the WSFC Group Id of the Availability Group.

Returns a row for every availability replica (regardless of join state) of the Availability Groups in the Windows Server Failover Cluster. Is sql server a database Since the AG’s id is not exposed in this DMV you have to join to sys.dm_hadr_availability_replica_cluster_nodes via sys.dm_hadr_availability_replica_cluster_states.replica_server_name or sys. Sql server 2000 tutorial dm_hadr_availability_replica_cluster_states.node_name. Sql server express edition 2005 Likewise you can also join to dm_hadr_availability_group_states.primary_replica on replica_server_name to get the group_id for the Availability Group or to sys.dm_hadr_name_id_map.ag_name = dm_hadr_availability_replica_cluster_nodes.group_name to also return the ag_id value. Miscrosoft sql server This is one area where Microsoft was not consistent in it’s Dynamic Management Object / System Catalog View naming conventions. For in sql server 2008 In one DMV you see a column called ag_name – in another it’s referred to as group_name. Sql server express 2008 with tools You can use any of these joins in reverse to humanize an exposed ag_id, say in sys.dm_hadr_availability_group_states, to an ag_name.

This DMV is most useful when needing to rationalize the replica_id in various DMVs back to a meaningful name – in this case the server name for the replica as represented in the replica_server_name column. Sql server maintenance An example of using this DMV is provided under dm_hadr_availability_group_states, which is covered further in this article.

This DMV returns a row showing the state of each local and remote availability replica in the same Availability Group as the local replica against which the query is executed. Ms sql server free It’s best to execute this against the host for the primary replica in order to assure the most complete picture possible of the state of all replicas participating in the AG. Sql server versions If you execute queries on sys.dm_hadr_availability_replica_states against the host for any of the secondary replicas you’ll only return local information for the availability group (the secondary node being queried against.)

sys.dm_hadr_database_replica_states returns a row for each database participating in an Availability Group and provides state information on both the primary and secondary replicas. Sql for sql server On a secondary replica, this view returns a row for every secondary database on the server instance. Ms sql server 2005 On the primary replica, this view returns a row for each primary database and an additional row for the corresponding secondary database. Sql server t sql So expect two rows returned for each database when executing on a primary replica but only one – and for the values associated with the secondary replica of the database – when executed against the secondary replica’s host. Sql server 2012 express limits Also, Microsoft makes clear that the values of the end_of_log_lsn, last_hardened_lsn, last_received_lsn, last_sent_lsn, recovery_lsn, and truncation_lsn columns are not actual log sequence numbers (LSNs). Ms sql server syntax Instead these are actually a log-block ID padded with zeroes. Sql server where Log blocks are the physical containers for those Virtual Log Files (or VLF’s) that you keep hearing about. Ms sql server 2012 express Of the LSN values returned by sys.dm_hadr_database_replica_states, only last_redone_lsn is a real LSN.

Availability Groups are a powerful replacement to SQL Server Database Mirroring and though complex in configuration and creation once configured you do have insights into their state thanks not only to the GUI objects inside SQL Server Management Studio – but also through Transact SQL and the SQL Server Dynamic Management Views as well. Sql server 2008 express r2 I hope you enjoyed this overview. Migrate sql express to sql server Going forward expect to see how we can use each of these DMOs together and separately to assess and solve your high availability implementations in SQL Server 2016… Sql server cost and beyond.

banner