The Data Flow Task moves data from sources to destinations with some transforms in between. When you are running a Data Flow in development, it might seem difficult to determine if the data is being transformed correctly. The columns might not be passed through the Data Flow at all.
You could open the destination to check on the status of the data, but this approach might not always be the best solution. Imagine a Data Flow with dozens of transforms moving thousands of rows to a destination. Opening the destination shows the columns are not showing the data you expected. Which transform is causing the problem? It may be hard to determine by just examining the data in the destination. This situation is where Data Viewers make tracking data changes much easier. Data Viewers are a development tool used to glance at the data during the Data Flow execution phase of a package. They cause a small popup window to show the data at certain points in a Data Flow.
Data Viewers should be removed before moving a package to production to be scheduled to run. If the Data Viewer remains on a package, the package will not stop at the point the Data Viewer is called, and the Data Viewer will load in memory and use unnecessary buffers.
To create a Data Viewer on a Data Flow, double-click the green or red line that connects the tasks in the Data Flow. This opens the Data Flow Path Editor, as shown in Figure 40-1. In the General node you find the common properties of the Data ...