Availability Groups

Availabilty groups

Availability Groups define a set of two (2) or more failover partners known as Availability Replicas. Each replica hosts a copy of the availability databases in the availability group. Every availability replica is assigned an initial role, either primary or secondary, which determines whether it hosts read-write databases (Primary) or read-only databases (Secondary).

Replicas are hosted on different servers and can be synchronized in two (2) modes (Asynchronous or Synchronous). The following cards display latency-specific information on the duplication of transactions for all Primary and Secondary Replicas on an ongoing basis.

• Use the Instance, Database, and Tag drop-down Page Filters to change the visualization to reflect the applied filter.
• Use the calendar widget to change the date range (default is last seven (7) days). The selected range is displayed in the widget.

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Primary replica latency

This card displays latency data by Instance for the Primary Replica.

• Bytes Sent to Replica/sec. are displayed by Throughput and Instance with sortable columns. Select the row to display details for Replicas within that Throughput range.
• Log Send Queue counter displays the number of log records in the primary database (in kilobytes) that have not yet been sent to the secondary replica by Instance in sortable columns. This value is sent to the secondary replica from the primary replica. Select the row to display scores for Replicas within that Throughput range.

Hover the cursor over the column headings to sort the list in ascending or descending order.

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Secondary replica latency

This card displays latency data by Instance for the Secondary Replica.

• Redone Bytes/sec. are displayed by Throughput and Instance with sortable columns. Select the row to display details for Replicas within that Throughput range.
• Redo Queue Latency counter displays the number of log records in the secondary replica, by Throughput and Instance with sortable columns, that have not been redone . Select the row to display scores for Instances within that Throughput range.

Hover the cursor over the column headings to sort the list in ascending or descending order.

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Primary replicas

The Primary Replica makes the primary databases available for read-write connections and sends the transaction log records of each primary database to every secondary database. Data is synchronized at the database level. This card displays information from the SQL Server that is stored in DVMs.
Results are grouped in a searchable table format with sortable columns, as follows:

• The Health column displays a color-coded Health Score icon indicating the general status of the replica.
• The Instance column displays the name of the Replica. An instance can be used for multiple Availability Groups.
• The Database column displays the name(s) of the Database(s) within the Availability Group.
• The Availability Group column the availability group name.
• The Availability Mode column displays the mode of data synchronization (synchronous or asynchronous) for the Availability Group. This determines whether the primary replica waits to commit transactions on a database until a given secondary replica has written the transaction log records to disk (hardened the log).
• The Replica Health State column displays information from the SQL Server on the status of the Replica. Select the score to see
• The Unhealthy Databases column displays the count of unhealthy databases in the Availability Group.
• The Avg. MB Sent to Replica column displays the average rate at which the Primary Replica Instance sent data during the collection range, in kilobytes/second.
• The Failovers column displays transitions of Secondary Replicas to the primary role (and former Primary Replicas to the secondary role) within the selected time range.
• The Last Updated column displays the time of the last collection from that server.

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Secondary replicas

Secondary Replicas are always read-only. This card lists all non-primary Replicas in a searchable table format with sortable columns, as follows:

• The Health column displays a color-coded Health Score icon indicating the general status of the replica.
• The Instance column displays the name of the Replica. An instance can be used for multiple Availability Groups.
• The Database column displays the name(s) of the Database(s) within the Availability Group.
• The Availability Group column the availability group name.
• The Availability Mode column displays the mode of data synchronization (synchronous or asynchronous) for the Availability Group. This determines whether the primary replica waits to commit transactions on a database until a given secondary replica has written the transaction log records to disk (hardened the log).
• The Replica Health State column displays information from the SQL Server on the status of the Replica. Select the score to see
• The Unhealthy Databases column displays the count of unhealthy databases in the Availability Group.
• The Avg. MB Sent to Replica column displays the average rate at which the Primary Replica Instance sent data during the collection range, in kilobytes/second.
• The Failovers column displays transitions of Secondary Replicas to the primary role (and former Primary Replicas to the secondary role) within the selected time range.
• The Last Updated column displays the time of the last collection from that server.