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:
- 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.
- 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:
- 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.
- 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.
- 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:
- 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.
- 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.