Professional SQL Server™ 2005 Integration Services

10.3. Enterprise Workflows with the Control Flow

Both of the components of the Control Flow have been discussed in Chapter 3 as well as the different types of precedence constraints. Since the Control Flow contains standard workflow concepts that are common to most scheduling and ETL tools, including DTS, the rest of this chapter will focus on the Data Flow; however, a brief look at the Control Flow parallelization and processing is warranted.

The Control Flow, as has already been mentioned, can be designed to execute tasks in parallel or serial, or a combination of the two. Tasks also are synchronous in nature, meaning that the task requires completion before handing off operation to another process. While it is possible to design a Control Flow that contains tasks that are not connected with constraints to other tasks, the tasks are still synchronously tied to the execution of the package. Said in another way, a package cannot kick off the execution of a task and then complete execution while the task is still executing. Rather, the SSIS execution thread for the task is synchronously tied to the task's execution and will not release until the task completes successfully or fails.

The synchronous nature of tasks should not be confused with the synchronous and asynchronous nature of transformations in the Data Flow. The concepts are slightly different. In the Data Flow, a transformation's synchronicity is a matter of communication (how data is passed between transformations) rather ...