Analyze the reports that provide the database record information
so that you can understand the statuses of database records in the
DEDB area.
Before you begin
Ensure that you can access the following reports for the
subject DEDB area:
DB Record Profile Analysis report
DB Record Placement Analysis report
Segment I/O Analysis report
Segment Placement Analysis report
Largest Database Records report (optional)
Not all utilities of IMS Fast
Path Solution Pack can produce this report. Use the appropriate utilities
and runtime options to generate these reports.
For details about the utility options and reports that can be generated, see the topic "Generating the analysis reports" in the IMS Fast Path Solution Pack: IMS High Performance Fast Path Utilities
User's Guide.
About this task
One of the most important tasks in
analyzing DEDB areas is analyzing the database record profile. The
process of analyzing a database record profile includes reviewing
the effect on I/O efficiency that might be caused by the changes in
database record characteristics. Results from this analysis are the
key factors for determining the best approach to resolve the exceptions.
In
this task, you will review the average length of the database records
and then review the patterns and statistics of database record overflow.
You will also review the database record overflow at the segment occurrence
level. These factors help you learn how I/O efficiency is affected
by segment overflow.
Optionally, if you identify a large database
record while reviewing the length of database records, you will also
learn how to obtain more information about such records. You will
also learn how to obtain information about database records at the
UOW level.
By completing this task, you will determine whether
the database record profile has been changed and whether the change
might affect I/O efficiency.
Procedure
Complete the following steps to
understand the statuses of database records in the area:
Check the average length of database
records.
The DB Record Profile Analysis report provides
statistics about the number and length of the database records and
statistics about the frequencies and length of segment occurrences.
The following figure is an example of the DB Record Profile Analysis report.
The DB Record Profile Analysis report provides information
that helps you determine whether to expand CI size and to calculate
the optimal values for the ROOT and UOW parameters for the DBD.
Generally,
if the average database record length multiplied by the average number
of root segments on a RAP is less than the current CI size, the CI
size is appropriate. If the calculated value significantly exceeds
the current CI size, consider tuning the CI size and UOW definition,
changing the randomizer, or both.
Tip: The average
number of root segments on a RAP can be found in the Roots per RAP
Distribution Graph. See Analyzing the randomizing routine.
Analyze the patterns and statistics of database record
overflow.
The DB Record Placement Analysis report includes
statistics about the number of database records that are contained
in each of the following seven placement categories:
Records that are placed only in BASE section
Records that are placed in BASE and DOVF sections
Records that are placed in BASE, DOVF, and IOVF sections
Records that are placed in BASE and IOVF sections
Records that are placed only in DOVF section
Records that are placed in DOVF and IOVF section
Records that are placed only in IOVF section
The following figure is an example of the DB Record Placement
Analysis report.
The DB Record Placement Analysis report provides information
that helps you determine whether to expand CI size and whether to
change the UOW definition in the DBD.
In an ideal
area, all database records reside only in the BASE section. If many
database records reside outside of the BASE section, you must review
other reports to further investigate the cause of overflow and to
avoid many database records overflowing to IOVF.
Check the database record overflow in segment occurrence
level.
Browse the Segment Placement Analysis report.
The Segment Placement Analysis report provides an overview of where
the segments reside in the area, especially occurrences of segment
types that contribute to overflow usage. This report provides proportion
of the segments that reside in RAA BASE, DOVF, and IOVF for each segment type.
The following figure is an example of the Segment Placement Analysis report.
Determine how I/O efficiency is affected
by segment overflow.
The Segment I/O Analysis report
provides information about the database record I/Os in the granularity
of the number of segment I/Os.
This report provides the following
statistics:
Contribution of occurrences of each segment type to a database
record
The number of physical I/Os that are required to retrieve the
root segment
The number of physical I/Os that are required to retrieve an occurrence
of each segment type
The number of physical I/Os that are required to retrieve an entire
database record
The Segment I/O Analysis report provides information that
is useful for evaluating the database I/O performance requirements
for specific user transactions. It is also used to validate the effects
of UOW and ROOT value parameter changes.
The following
figure is an example of the Segment I/O Analysis report. The report
shows the average, standard deviation from the average, maximum, and
minimum number of I/Os to read a database record or a root segment.
Optional: Obtain more information
about large database records.
Tuning an area
of a database that has exceptionally large database records can be
difficult.
You can obtain a list of database
records and information about these records by browsing the Largest
Database Records report. This report lists the database records in
descending order by their size, which can help you identify the database
records that are exceptionally large.
The following figure is
an example of the Largest database Records report.
Each entry of the table in this report includes the following key information about a large
database record:
The total length of the database record, which includes prefix length of all segment occurrences
in the record
The total number of segment occurrences in the record
The RBA value of the RAP on which the database record was randomized
The RBA value of the root segment of the database record, which shows how far from the RAP or
RAP CI the database record is
The value of the root sequence key of the database record
You might use this information in a later step (Tuning DEDB areas)
when you tune the area and the randomizing routine.
Optional: Analyze the database record profile
at the UOW level.
To obtain more information about the
database record profile at the UOW level, generate and review the
UOW report.
Generally, if the packing density of RAA BASE (observed
in Step 5 in Analyzing free space usage) is high,
and if the average number of physical I/Os (observed in Step 4)
is also high, consider expanding the size of RAA BASE.
If the average
lengths of database records is relatively high compared to the current
CI size (observed in Step 1 and
Step 5),
you might also consider changing the CI size. In addition, because
long RAP synonym chains can also increase the average number of physical
I/Os that are required to retrieve a root or a database record, and
might have an influence in determining the optimal CI size, you must
check the randomizing efficiency before determining your actions.
For randomizing analysis, see Analyzing the randomizing routine.