TAILIEUCHUNG - Brad’s Sure Guide to SQL Server Maintenance Plans- P48

Brad’s Sure Guide to SQL Server Maintenance Plans- P48: SQL Server has a reputation as being a simple database application to install, configure, and maintain. This is a little misleading. SQL Server is a powerful relational database that can handle the needs of the largest organizations and, as such, its proper maintenance almost certainly requires the attention of an experienced DBA. | Chapter 18 Subplans and Precedence Figure Notice that the green arrow starts at the Backup Database Task and points at the Maintenance Cleanup task. The arrow always must originate at the precedent task Back Up Database which will execute first and terminate at the dependent task Maintenance Cleanup which will execute second depending on any imposed conditions. The conditions are imposed inside the precedence arrow itself and in fact the green color of this arrow in Figure indicates that the arrow is by default imposing an on success condition on the execution of the Maintenance Cleanup task. In other words the condition can be expressed as follows On success of the backup task execute the cleanup task. How do we verify this If you right-click on the green line and then select Edit or double-click on the green line the Precedence Constraint Editor screen appears as shown in Figure . 236 Chapter 18 Subplans and Precedence Figure The Precedence Constraint Editor is used to help you establish the types of precedence that are available. There are quite a few options on this screen but it turns out that we can ignore most of them. The Precedence Constraint Editor screen looks more complicated than it really is because it includes options that aren t really applicable to creating Maintenance Plans. Like much of the code used by the Maintenance Plan Designer it is reused in different parts of SSMS and so certain options are presented out of context. For example the Expression option available as an Evaluation operation is really designed to create SS1S packages not Maintenance Plans. The only option with which we really need to be concerned is Value. By default Success is selected in the drop-down list and this is the origin of the green color of the arrow in Figure . Only if the Back Up Database task executes successfully will the Maintenance Cleanup task execute. There are two other options available in the Values drop-down list namely .

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