Understanding the WMI Provider for Server Events
SQL Server 2005 includes the WMI Provider for Server Events. This provider lets you use the Windows Management Instrumentation (WMI) to monitor events in SQL Server. The provider works by turning SQL Server into a managed WMI object. Any event that can generate an event notification in SQL Server can be leveraged by the WMI by using this provider. Additionally, as a management application that interacts with the WMI, SQL Server Agent can respond to these events, increasing the scope of events covered by SQL Server Agent over earlier releases.
Management applications such as SQL Server Agent can access SQL Server events using the WMI Provider for Server Events by issuing WMI Query Language (WQL) statements. WQL is a simplified subset of structured query language (SQL), with some WMI-specific extensions. In using WQL, an application retrieves an event type against a specific database or database object. The WMI Provider for Server Events translates the query into an event notification, effectively creating an event notification in the target database. For more information about how event notifications work in SQL Server, see Event Notifications (Database Engine). The events that can be queried are listed in WMI Provider for Server Events Classes and Properties.
When an event occurs that triggers the event notification to send a message, the message goes to a predefined target service in msdb that is named SQL/Notifications/ProcessWMIEventProviderNotification/v1.0. The service puts the event into a predefined queue in msdb that is named WMIEventProviderNotificationQueue. (Both the service and the queue are created dynamically by the provider when it first connects to SQL Server.) The provider then reads the event data from this queue and transforms it into managed object format (MOF) before returning it to the application. The following illustration shows this process.
For example, consider the following WQL Query:
SELECT * FROM DDL_DATABASE_LEVEL_EVENTS WHERE DatabaseName = 'AdventureWorks'
In response to this query, the WMI Provider for Server Events creates the equivalent event notification in the target database:
USE AdventureWorks ; GO CREATE EVENT NOTIFICATION SQLWEP_76CF38C1_18BB_42DD_A7DC_C8820155B0E9 ON DATABASE WITH FAN_IN FOR DDL_DATABASE_LEVEL_EVENTS TO SERVICE 'SQL/Notifications/ProcessWMIEventProviderNotification/v1.0', 'A7E5521A-1CA6-4741-865D-826F804E5135'; GO
In this example,
SQLWEP_76CF38C1_18BB_42DD_A7DC_C8820155B0E9 is a Transact-SQL identifier that is made up of the prefix
SQLWEP_ and a GUID.
SQLWEP creates a new GUID for each identifier. The value
A7E5521A-1CA6-4741-865D-826F804E5135 in the
TO SERVICE clause is the GUID that identifies the broker instance in the msdb database.
For more information about how to work with WQL, see Using WQL with the WMI Provider for Server Events.
Management applications direct the WMI Provider for Server Events to an instance of SQL Server by connecting to a WMI namespace that is defined by the provider. The Windows WMI service maps this namespace to the provider DLL, Sqlwep.dll, and loads it into memory. The provider manages a WMI namespace for Server Events for each instance of SQL Server 2005, and the format is: \\.\root\Microsoft\SqlServer\ServerEvents\instance_name, where instance_name defaults to MSSQLSERVER. For more information about how to connect to a WMI namespace for an instance of SQL Server, see Working with the WMI Provider for Server Events.
The provider DLL, Sqlwep.dll, is loaded only one time into the WMI host service of the operating system of the server, regardless of how many instances of SQL Server are on the server.
For an example of a SQL Server Agent management application that uses the WMI Provider for Server Events, see Sample: Creating a SQL Server Agent Alert by Using the WMI Provider for Server Events. For an example of a management application that uses the WMI Provider for Server Events in managed code, see Sample: Using the WMI Event Provider with the .NET Framework. More information is also available about WMI in the Microsoft .NET Framework SDK.