Monitoring SQL Server Database Mirroring with Email Alerts

Problem

The number of Database Mirror pairs in our enterprise is increasing at an alarming rate. With the ease of setup, resilience and ability to seamlessly failover and failback, database mirroring has taken over from log shipping as the DR solution of choice. We need a basic script that we can execute on all servers participating in mirroring that will alert us if any Principals or Mirrors are in an abnormal state. The script needs to work on both Principal and Mirror server.

Solution

The Catalog View sys.database_mirroring contains one row for each database in the instance of SQL Server and also contains state information of all mirrored databases. We’ll query this Catalog View and raise an email alert for each mirrored database that we find in an abnormal state. We don’t utilize a witness server in any of our mirrored pairs so we rely on manual failover.

Prerequisites

A valid Database mail profile
A valid login that has permission to send email i.e. a member of the DatabaseMailUserRole role in the msdb database
At least one pair of mirrored databases to monitor

The Script

Substitute in the below script your Database Mail profile and a suitable email address to receive the alerts.

DECLARE @state VARCHAR(30) 
DECLARE @DbMirrored INT 
DECLARE @DbId INT 
DECLARE @String VARCHAR(100) 
DECLARE @databases TABLE (DBid INT, mirroring_state_desc VARCHAR(30)) 
 
-- get status for mirrored databases 
INSERT @databases 
SELECT database_id, mirroring_state_desc 
FROM sys.database_mirroring 
WHERE mirroring_role_desc IN ('PRINCIPAL','MIRROR') 
AND mirroring_state_desc NOT IN ('SYNCHRONIZED','SYNCHRONIZING') 
 
-- iterate through mirrored databases and send email alert 
WHILE EXISTS (SELECT TOP 1 DBid FROM @databases WHERE mirroring_state_desc IS NOT NULL) 
BEGIN 
   SELECT TOP 1 @DbId = DBid, @State = mirroring_state_desc 
   FROM @databases 
   SET @string = 'Host: '+@@servername+'.'+CAST(DB_NAME(@DbId) AS VARCHAR)+ ' - DB Mirroring is '+@state +' - notify DBA' 
   EXEC msdb.dbo.sp_send_dbmail 'valid_mail_profile', 'DBA@mssqltips.com', @body = @string, @subject = @string 
   DELETE FROM @databases WHERE DBid = @DbId 
END 
 
--also alert if there is no mirroring just in case there should be mirroring :)
SELECT @DbMirrored = COUNT(*) 
FROM sys.database_mirroring 
WHERE mirroring_state IS NOT NULL 
IF @DbMirrored = 0 
BEGIN 
   SET @string = 'Host: '+@@servername+' - No databases are mirrored on this server - notify DBA' 
   EXEC msdb.dbo.sp_send_dbmail 'valid_mail_profile', 'DBA@mssqltips.com', @body = @string, @subject = @string 
END

Practice

To verify the alert let’s pause mirroring through the SQL Server Management Studio (SSMS). In Object Explorer right click your mirrored database > Properties > Mirroring option > Pause button as follows:

Now, if the query finds a mirrored database in an abnormal state as shown below, it will send out an alert email alert:

The script will also output the following information to notify you that an alert has been sent to be processed by Database Mail.

Mirroring Alert Message
-----------------------
Host: SERVERXXX.MirrorTest - DB Mirroring is Suspended - notify DBA
 
Mail queued.
 
 
Mirroring Alert Message
-----------------------
Host: SERVERXXX.sp_config_ssp2 - DB Mirroring is DISCONNECTED - notify DBA
 
Mail queued.

Email received that clearly shows the host name, database name and the abnormal state of the mirroring so that the DBA team can investigate further.

Next Steps

You can schedule this simple script as a SQL job to run every few minutes to monitor and alert on the state of your mirroring.
Use the Database Mirroring Monitor in SSMS to set various warning thresholds that will raise events to the Application Event Log. These events can be monitored by your enterprise monitoring tool or through SSMS.
Review this excellent tip on automating database mirroring failover for multiple databases.
Check out the following tips

Alan Cranfield

Versatile SQL SERVER DBA with over 10 years’ experience managing critical production systems in large distributed enterprise environments. Specialise in SQL Server database administration and configuration on a large scale and the design of robust strategies for the maintenance and management of Very Large Databases primarily within the financial services industry. Have undertaken DBA work in 4 continents in the Banking, Gaming and Insurance sectors as well as 3 years with NYSE in London where I was the Lead SQL Server DBA for NYSE LIFFE™, the global derivatives business of the NYSE Euronext group. Currently living in Shanghai where I was recently asked by Microsoft to assist with the transition of an eCommerce operations team from US to China.

Prerequisites

The Script

Practice

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