What IMS cannot recover

IMS can automatically recover from some errors, and IMS provides mechanisms to allow you to recover from many more errors, but there are some errors IMS cannot recover.

Generally, these unrecoverable errors are of two types:

• Application logic or input errors

  When you detect an error caused by an application program that is running, backing out the faulty data is fairly simple. But if that program is given the wrong input or is constructed with logic errors, you might not be able to detect such problems because the program will run to completion. After the application program has finished running (or has committed its data), the faulty data can be used by other programs, and the problem can spread throughout your system.

  IMS has no automatic or guaranteed way to back out committed data. You might be able to back out the data manually (for example, by editing individual records in the affected databases), but such a process is likely to be difficult. And the more time that passes after the original errors are introduced, the more programs are likely to have used the bad data, and the less likely your chances of success. Moreover, output that has been produced or actions taken as a result of the faulty data will already be outside the boundaries of the databases.

  Recommendation: To minimize application logic or input errors, you should extensively test new applications (both individually and in an integrated system test) before bringing them online. Extensive validation of user input by application programs also helps minimize input errors.
• Operational errors, including misuse (accidental or malicious) of the IMS recovery facilities
  Successful recovery requires both proper operation of IMS on a daily basis and proper use of the recovery facilities. This proper use includes such things as:

  • Using the correct data sets
  • Avoiding improper job cancellations during regular operations
  • Regularly maintaining the logs
  • Using the correct log volumes in the correct sequence
  • Using the appropriate utilities at the appropriate time

  You should have no difficulties in operating IMS properly, and other topics in this information explain how to set up the necessary procedures and guidelines. However, if you operate IMS, its recovery facilities, or both, improperly, IMS might not be able to correct problems introduced by such improper use.