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Use RECOVER parameter to get better restarts after system failures

The RECOVER parameter can play a critical role in repairing access paths after a system failure.

Ron Turull

Last time, we discussed the MAINTparameter of the Create Logical File (CRTLF) command. Using this parameter effectively can increase your system's performance. But don't overlook the RECOVER parameter, either. Although this parameter does not affect day-to-day processing like the MAINT parameter does, it does play a critical role during what most shops consider a very critical time: during recovery after a system failure.

There are three periods of a system recovery during which a damaged access path can be repaired or rebuilt:

  1. During the IPL.
  2. After the IPL but before any jobs are allowed to open the file.
  3. During the first open of the associated file.

The RECOVER parameter accepts one of three values, permitting you to select the recovery phase during which you want the access path rebuilt. The three values are as follows:

  1. *IPL. Use this value for critical files. No user jobs are allowed to start until all files with RECOVER(*IPL) have had their access paths rebuilt.
  2. *AFTIPL. This is the default for files that require unique keys. Users' jobs are allowed to start and run while these files are being processed. However, if a job tries to use a file that is undergoing access path rebuild, the job (i.e., program) will receive an exception message. So, be careful; you may want to build in some file-exception handling into any program that uses a file with RECOVER(*AFTIPL) or specify RECOVER(*IPL) instead.
  3. *NO. This is the default for files that do not require unique keys. The file's access path is rebuilt the next time the file is opened. The program that opens the file will wait while the access path is rebuilt.

For physical files, too
These two CRTLF command parameters -- MAINT and RECOVER -- are also a part of the CRTPF command (Create Physical File). This, of course, is because physical files can have keyed access paths as well. All the same rules apply so think about hitting F4+F9 when creating physical files, too.

About the author: Ron Turull is editor of Inside Version 5. He has more than 20 years experience programming for and managing AS/400-iSeries systems.


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