HD Pointer Checker online considerations

HD Pointer Checker can run for IMS online databases. However, HD Pointer Checker might not generate accurate results under certain conditions. Incomplete insert, replace, or delete operations typically cause HD Pointer Checker to detect false pointer errors.

To increase the likelihood of achieving accurate results, the following three methods are provided:

Running HD Pointer Checker for IMS online databases while the databases are not being updated or, at least, when the databases are scarcely updated

If HD Pointer Checker detects pointer errors in IMS online databases, try running HD Pointer Checker again for the databases. If the pointer error was caused by an incomplete database update operation, the error might not be present in the second run. However, if the same pointer error is detected in the same pointer in the second run, the database likely has a pointer error.

Consecutive HD Pointer Checker run listings must be compared. Whenever the same error message occurs on two consecutive run listings, you can be sure it is a real error. Then analyze the errors and repair the databases. How to do this is described in Database repair guidelines. All error messages that are not present on the following HD Pointer Checker run are quite likely to be a result of incomplete database updating. Typically, you can ignore such error messages because they do not represent database corruption. Although this technique is cumbersome and error-prone, it can be used successfully with due attention.

Running HD Pointer Checker while the database is quiesced

To keep the database online as much as possible and achieve accurate pointer checking results, you can use the database quiesce function and the FlashCopy® function. The FlashCopy function requires less time to create a copy of data set. For example, you can make the database quiesced and take an image copy with the FlashCopy function. When the image copy is taken, release the quiesce (the database becomes available when quiesce is released) and run HD Pointer Checker for the image copy data set. In this way, you can shorten the time that a database is unavailable.

The advantage of this method is that you can achieve accurate pointer checking results. However, this method requires additional DASD space for FlashCopy, and you must run separate steps to quiesce the database, create FlashCopy, and run pointer check.

For information about the database quiesce function, see IMS Operations and Automation.

Running IMS HP Image Copy in pseudo online pointer check mode

IMS HP Image Copy provides the functions to make online databases temporarily unavailable (they are taken offline or quiesced) and to run HASH checking. Pseudo online pointer check mode uses these IMS HP Image Copy functions to provide accurate HASH checking results for online databases.

The advantage of this method is that you can achieve accurate pointer checking results within one IMS HP Image Copy job step. Therefore, you do not need to manually issue IMS commands to stop or restart the databases. The disadvantages are that additional DASD space is required for FlashCopy, and only HASH checking is available.

The following restrictions apply to HASH checking:
  • HASH checking checks the pointers briefly. If a pointer error is detected in an IMS HP Image Copy job, stop the database and run HDPC stand-alone job for the database to analyze the pointer error.
  • For HALDBs, HASH checking checks the physical pointers, but it does not check the logical pointers and PSINDEX databases.
Here is a sample scenario to efficiently check the pointers by using pseudo online check mode: Run the IMS HP Image Copy job in pseudo online pointer check mode for online databases on a regular basis, and run HD Pointer Checker stand-alone job for offline databases during the batch window.

For details about pseudo online pointer check mode, see "Pointer checking for online full-function databases" in the IMS High Performance Image Copy User's Guide.