The save-while-active (SWA) feature allows users to resume activity after save processing reaches a certain point. i5/OS refers to this point as the synchronization checkpoint. By using the save-while-active feature, you can reduce application downtime and increase user access to selected data or applications.
To use the save-while-active feature with a save that does not use journaling or commitment control, you need to prevent user access until BRMS reaches the synchronization point. Once the system reaches the checkpoint, the system releases the exclusive locks on the library, and users can resume normal activity. Meanwhile, BRMS continues to save the data.
If you have large libraries with single member physical files, it may take less time to reach the checkpoint than it takes to save the data to tape. For example, suppose you have a library that contains single member physical files and that it takes an hour to save. During regular save processing, the system locks the library, which prevents user access to any file in that library until the save completes. By using the save-while-active feature, users can access library files after BRMS reaches the checkpoint. Suppose, in this example, that BRMS reaches the checkpoint in 20 minutes. In this example, the save-while-active feature increased your application availability by nearly 40 minutes. IBM cannot determine the exact time at which BRMS reaches the checkpoint. The exact time depends on the size of the library or application to which you are applying save-while-active. Under most circumstances, however, the time it takes to reach the checkpoint is notably shorter than the time it takes to save the entire library or application.
This section provides several examples of how you can apply save-while-active to your save strategy. However, this section does not cover every topic associated with save-while-active. Therefore, you should review Backing up your system topic in the IBM i Information Center for more information before implementing save-while-active.