Analyzing fragmentation exceptions for HISAM and SHISAM databases

Analyze the fragmentation exceptions that were detected for HISAM and SHISAM databases.

Before you begin

Ensure that you can access the Sensor Data Statistics report that contains the latest sensor data. If you cannot access this report, run the FF DB Sensor Printing utility to generate the report.

About this task

In the following procedure, you will analyze each fragmentation exception that you received for HISAM and SHISAM databases.

For each exception that was reported, you will first identify the relevant data elements to understand the condition of the database. Then, for HISAM databases, you will analyze the relevant IMS Tools reports to learn more about the database state. Finally, if you use Management Console or Administration Console and if relevant sensor data charts are available, you will analyze historical trends of sensor data to understand the trend characteristics of the sensor data that was obtained from the database data sets.

By completing these steps, you will identify the type of fragmentation symptoms that occurred and the database data set for which the exceptions were reported.

Procedure

In this section, instructions to analyze the common fragmentation exceptions are provided. Follow the instructions for the exceptions that you received. The most common exceptions are listed first.
Exception class name: EXCESSIVE_CI_OR_CA_SPLITS
This exception indicates that the number of CI splits, CA splits, or both are high, and that the VSAM KSDS file is fragmented.
The data set of SHISAM databases and the primary data set of HISAM databases are VSAM KSDSs. As data is updated in VSAM KSDS files, control interval (CI) and control area (CA) splits occur. A condition where excessive CI and CA splits exist indicates that the data set is fragmented. CI and CA splits do not occur in overflow data sets because overflow data sets are VSAM ESDSs.
An excessive number of CI splits and CA splits might affect the I/O performance efficiency of applications that perform a massive amount of sequential reading. For information about the effects of an excessive number of CI splits or CA splits, see the topic "Optimizing Free Space Distribution" in z/OS® DFSMS Using Data Sets.
Complete these steps to analyze this exception:
  1. Locate the following data elements in the Sensor Data Statistics report:
    DB_NUM_CI_SPLIT
    The value for this data element indicates the number of split CIs.
    DB_PCT_NUM_CI_SPLIT
    The value for this data element indicates the percentage of split CIs compared to the total number CIs.
    DB_NUM_CA_SPLIT
    The value for this data element indicates the number of split CAs.
    DB_PCT_NUM_CA_SPLIT
    The value for this data element indicates the percentage of split CAs compared to the total number of CAs.
  2. Optional: To view the trend of data over time, locate the following charts in Management Console or Administration Console:
    • CA Splits chart
    • CI Splits chart

    Understanding the trend over time can help you anticipate the future behavior of the data sets. Use this knowledge to determine when you might need to take preventative action and to establish efficient maintenance plans.

You have now obtained information about the current database state that caused this exception. You will use this information later to determine the appropriate action to resolve the exception.
In Step b, you also identified the sensor data charts that can help you establish maintenance plans to prevent this exceptional state from occurring in the future.
Exception class name: EXCESSIVE_HISAM_DELETE_SEGM
This exception indicates that too many segments whose delete flag is set to ON exist. These segments have already been deleted, but they still exist in the database. These segments waste space and increase the number of I/O operations.
For information about the effects of delete segments, see the topic "Deleting segments" in IMS Database Administration for the version of IMS that you are using.
Complete these steps to analyze this exception:
  1. Locate the following data elements in the Sensor Data Statistics report:
    DB_NUM_DELSEG
    DB_PCT_NUM_DELSEG
    The values for these data elements indicate the number of segments whose delete flag is set to ON and the percentage of these segments compared to the total bytes of used blocks in the data set.
  2. Optional: To obtain more information about these segments, run the HD Pointer Checker utility of IMS HP Pointer Checker, or IMS HP Image Copy with the HDPC=YES option, and generate the HISAM Data Set Statistics report.

    By reviewing this report, you can determine how many deleted segments exist for each segment type. You can also identify the length of each segment, which helps you identify the amount of space that is occupied by the deleted segments. In addition, you can identify the segment level for each segment type. If segment types whose segment level is high have many deleted segments, I/O performance can be affected.

  3. Optional: To view the trend of data over time, locate the Deleted Segment chart in Management Console or Administration Console.

    Understanding the trend over time can help you anticipate the future behavior of the data sets. Use this knowledge to determine when you might need to take preventative action and to establish efficient maintenance plans.

You have now obtained information about the current database state that caused this exception. You will use this information later to determine the appropriate action to resolve the exception.
In Step c, you also identified the sensor data chart that can help you establish maintenance plans to prevent this exceptional state from occurring in the future.
Exception class name: FRAGMENTED_FREE_SPACE
This exception indicates an excessive amount of fragmented unusable IMS free space. Fragmented unusable IMS free space is fragmented space that is too small to store the shortest segment that is defined in the DBD definition.
Complete these steps to analyze these exceptions:
  1. Locate the following data element in the Sensor Data Statistics report:
    DB_AVG_NUM_FSE
    The value of this data element indicates the average number of IMS free space fragments in a CI.
    This data element is reported for each data set. Locate the data element values for each data set, and identify the data sets for which this exception was reported.

    Also, locate the following data elements. These data elements help you understand more about the amount of remaining free space that IMS can use.

    DB_NUM_FSE_MIN
    The value of this data element indicates the number of IMS free space fragments in which the shortest segment that is defined in the DBD definition can be stored.
    DB_NUM_FSE_MAX
    The value of this data element indicates the number of IMS free space fragments in which the longest segment that is defined in the DBD definition can be stored.
    DB_NUM_FSE
    The value of this data element indicates the number of IMS free space fragments.
    DB_BYTES_FREE_SPACE
    The value of this data element indicates the total bytes of free space.

    These data elements are reported for each data set. Locate the data element values for each data set, and identify the data sets for which this exception was reported.

  2. Optional: To view the trend of data over time, locate the following charts in Management Console or Administration Console:
    • Unusable IMS Free Space chart
    • Usable IMS Free Space chart

    Understanding the trend over time can help you anticipate the future behavior of the data sets. Use this knowledge to determine when you might need to take preventative action and to establish efficient maintenance plans.

You have now obtained information about the current database state that caused this exception. You will use this information later to determine the appropriate action to resolve the exception.
In Step b, you also identified the sensor data charts that can help you establish maintenance plans to prevent this exceptional state from occurring in the future.

What to do next

If you received other exceptions that belong to other exception categories, see the following topics to determine your next step:

If the only exceptions that you received are fragmentation exceptions, continue with Resolving fragmentation exceptions for HISAM and SHISAM databases.