The SQL Server Agent can monitor events that occur on
the database server and automatically respond to these events with
alerts. Alerts can be fired based on SQL Server events, performance
conditions, and Windows Management Instrumentation (WMI) events. After
an alert is fired, the SQL Server Agent can respond by notifying an
operator or executing a job. This provides a proactive means for
identifying and reacting to critical conditions on a database server.
Defining Alert Properties
To define alerts, you select the SQL Server Agent node in the Object Explorer tree and then right-click on the Alerts node and select New Alert. Figure 1 shows an example of the New Alert dialog that appears.
Figure 1. The General page of the New Alert dialog.
The General page selected in Figure 1
allows you to define the basic alert properties, including the name of
the alert and type of event you want the alert to respond to. The
default type of alert, the SQL Server event alert, is triggered by SQL
Server events that write to the Windows Application event log. SQL
Server writes to the Application event log when the following events
When sysmessages errors with a severity of 19 or higher are generated. You can use the sys.sysmessages catalog view to view all the sysmessages that are stored in the server. You can create new user-defined messages by using the sp_addmessage stored procedure; they must have a msg_id
(or error number) that is greater than 50,000. The error message must
be created before you can reference the error number in an alert.
When sysmessages errors are generated by the database engine. These messages have error numbers lower than 50,000 and are installed by default.
When any RAISERROR statement is invoked with the WITH LOG option. The WITH LOG statement forces the event to be written to the Application event log. Messages generated with RAISERROR that have a severity level greater than 18 are required to write to the Application event log.
When sysmessages have been altered with the sp_altermessage statement to write to the application log. The sp_altermessage command has a write_to_logsys.messages. When the write_to_log parameter is set to WITH_LOG, these message automatically write to the Application event log, regardless of whether the WITH_LOG option is used when the error is raised. parameter that you can use to modify error numbers found in
When application calls are made to xp_logevent to log an event to the application log.
The bottom portion of the
General page of the New Alert dialog allows you to define which events
in the Application event log the alert should respond to. You can have
the event respond to a specific error number, the error severity level,
or specific text that is contained in the error message. The sys.sysmessages
catalog view contains a complete list of all the error message details
for all the supported languages. You can use the following SELECT statement to list the error messages for the English language:
SELECT * FROM SYS.SYSMESSAGES
where msglangid = 1033
order by msglangid, error
You can define an alert for
hundreds of messages. For example, you can define an alert that responds
to changes to database options. You do this by selecting error number
5084, which is triggered whenever a change is made to the database
options. You can also narrow the scope of the alert to look at a
specific database by using the Database Name drop-down. This limits the
alert to errors that occur in the specific database you choose. The
default option is to look at all databases.
The two other types of alerts
you can define are SQL Server performance condition alerts and WMI
event alerts. A SQL Server performance condition alert reacts to
performance conditions on the server. Figure 2 shows an example of this type of alert.
Figure 2. A SQL Server performance condition alert on the General page.
When you select a
SQL Server performance condition alert, you need to select the
performance object and counter for that object to monitor. The SQL
Server performance objects and counters available on the General page of
the New Alert dialog are a subset of those available in the Windows
Performance Monitor application. These performance metrics encompass key
indicators, such as memory, CPU, and disk space.
After selecting the object
and counter, you need to define the performance threshold for the alert
at the bottom of the General page, below the Alert if Counter label. In
the example shown in Figure 16.16, the alert is monitoring the transaction log file for the AdventureWorks database. The threshold has been set such that the alert will fire if the transaction log for this database rises above 2KB.
The WMI event alerts use WMI to
monitor events in an instance of SQL Server. The SQL Server Agent can
access SQL Server events by using the WMI provider for server events by
issuing WMI Query Language (WQL) statements. WQL is a scaled-down
version of SQL that contains some WMI-specific extensions. When a WMI
query is run, it essentially creates an event notification in the target
database so that a related event will fire.
shows an example of a WMI event alert. This example uses a WQL query
that detects any Data Definition Language (DDL) changes to any of the
databases on the server. After the alert is created, you can test it by
running a DDL statement against the database (for example, alter table Person.address add newcol int null).
Figure 3. The General page showing a WMI event alert.
Defining Alert Responses
The definition of an alert
has two primary components. The
first component involves the identification of the event or performance
condition that will trigger the alert. The second part of an alert
definition involves the desired response when the alert condition is
met. You can define an alert response by using the Response page on the
alert’s Properties screen. Figure 4 shows a sample response that has been configured to use NET SEND on a message to the operator named ChrisG.
Figure 4. Configuring an alert response.
Operator notification and
job execution are the two responses to an alert. Operator notification
allows for one or more operators to be notified via email, pager, or the
NET SEND command. Job execution allows for
the execution of a job that has been defined in the SQL Server Agent.
For example, you could execute a job that does a database backup for an
alert that is triggered based on database size. You can define both job
execution and operator notification in a single alert; they are not
You can further define an alert response by using the Options page of an alert’s Properties window (see Figure 5).
Figure 5. Alert options.
You can include an alert’s
error text in the operator notification message on this page. This alert
error text provides further details about why the alert was fired. For
example, if you have an alert that is triggered by changes to database
options, the alert error text would include the actual option that was
changed. You can also define additional notification text that is
included when the message is sent. This message could include directives
for the operators or additional instructions. Finally, you can define
the amount of time that the alert will wait before responding to the
alert condition again. You do this by using the Delay Between Responses
drop-downs (Minutes and Seconds) to set the wait time. This capability
is useful in situations in which an alert condition can happen
repeatedly within a short period of time. You can define a response
delay to prevent an unnecessarily large number of alert notifications
from being sent.