Analyze the Freespace Analysis report to understand the
status of free space usage of an area.
Before you begin
Ensure that you can access the Freespace Analysis report for the subject DEDB area. To
generate a Freespace Analysis report, 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
The amount of free space within each
area of a database and the distribution of that free space must be
monitored on a regular basis for the following reasons:
To avoid application failures that might be caused by out-of-space
conditions
To determine whether reorganization is required
To determine the optimal timing for database expansion
The Freespace Analysis report provides information that helps
you determine the optimal values for the UOW and ROOT parameters of
a DBD. The report also provides information for monitoring DOVF and
IOVF usage to determine the effectiveness of free space reorganization.
By
completing the steps in this topic, you can determine the following
free space characteristics of the area:
The total amount of free space in RAA BASE, DOVF, IOVF, and SDEP
The number and the size of the free space elements in RAA BASE, DOVF,
and IOVF
The relationship between available free space in each
section of the area and pointers to other sections, except for the
SDEP part and SDEP-related pointers
Procedure
Complete the following steps to
understand the status of free space usage of the area:
Determine the percentage of free space
in each section of the area.
Locate the overview section
of the Freespace Analysis report. This section provides information
about the free space that is available in each section of the area.
Free space availability is the first indicator that you should check.
The following figure shows an example of the overview section of the report.Figure 1. Overview section of the Freespace Analysis report
Determine the free space availability in RAA BASE and the
overflow from RAP CIs.
Locate the table for RAA BASE in the
report. This table shows the relationship between free space availability
in RAP CIs and overflow to DOVF and IOVF.
The following figure
shows an example of the RAA BASE
table in the report.Figure 2. RAA BASE table in the Freespace Analysis report
By analyzing the data in this table, you can identify
the state of the following free space characteristics:
%FS
The range of total free space percentages in a RAP CI in the RAA BASE
NO. CI'S
Distribution of RAP CIs by %FS range
NO. OF FSE'S
The number of the free space elements (FSEs) in RAP CIs for each
%FS range
SIZE OF FSE'S
The size of the FSEs in RAP CIs for each %FS range
#USE OVFLOW
The amount of RAP CIs that overflow to DOVF or IOVF for each %FS
range
PTR. TO DOVF
The amount of overflow to DOVF for each %FS range
PTR. TO IOVF
The amount of overflow to IOVF for each %FS range
You can determine if fragmented
free space elements exist by analyzing the total bytes of free space
in RAP CIs.
If the total number of bytes of free space in RAP CIs is sufficient,
but the number of free space elements that are smaller than the average
segment size has increased, you can assume that fragmented free space
elements exist.
If the total size of free space in RAP CIs is sufficient, but
the RAP CIs have many references to the DOVF or IOVF section, you
can assume that free space fragmentation or bulk deletion of segment
occurrences has occurred in the RAP CIs after overflow.
Determine to what extent UOWs are using
the DOVF and IOVF sections.
Locate the DOVF and IOVF
sections in the report. The following figure shows an example of the
DOVF and IOVF sections of the report.
Figure 3. DOVF and IOVF sections of the Freespace Analysis report
FREESPACE ANALYSIS - DOVF
%DOVF #UOWS % -DOVF CI'S USED -NO. OF FSE'S-- ----SIZE OF FSE'S---- --PTR TO BASE-- --PTR TO DOVF-- --PTR TO IOVF--
FREE UOW AVG S/D MAX MIN AVG S/D MAX MIN AVG S/D MAX MIN AVG S/D MAX MIN AVG S/D MAX MIN AVG S/D MAX MIN
100 13 20
90-99 0
80-89 1 2 1.0 .0 1 1 1.0 .0 1 1 753 0 753 753 0 0 0
70-79 13 20 1.0 .0 1 1 1.3 .5 2 1 383 174 502 76 0 0 2.2 2.9 11 0
60-69 0
50-59 0
40-49 0
30-39 0
20-29 29 45 2.0 .0 2 2 1.0 .3 2 0 238 182 502 0 0 .2 .5 2 0 .6 1.0 4 0
10-19 0
0-9 9 14 2.0 .0 2 2 0 0 0 1.0 1.2 4 0 1.3 1.5 4 0
DOVF USAGE SUMMARY
UOW'S USING DOVF: NO.: 52 %UOW'S: 80%
NO. DOVF CI'S USED: AVG: 1.73 SDEV : .44 MAX: 2 MIN: 1
FREESPACE ANALYSIS - IOVF
%DOVF #UOWS % #USE -IOVF CI'S USED -NO. OF FSE'S-- ----SIZE OF FSE'S---- --PTR TO BASE-- --PTR TO DOVF-- --PTR TO IOVF--
FREE UOW IOVF AVG S/D MAX MIN AVG S/D MAX MIN AVG S/D MAX MIN AVG S/D MAX MIN AVG S/D MAX MIN AVG S/D MAX MIN
100 13 20
90-99 0
80-89 1 2 0
70-79 13 20 10 1.3 1.0 3 1 .3 .5 1 0 323 291 753 0 0 0 .2 .4 1 0
60-69 0
50-59 0
40-49 0
30-39 0
20-29 29 45 22 1.3 1.1 4 1 .5 .5 1 0 305 283 945 0 0 0 .1 .4 2 0
10-19 0
0-9 9 14 6 1.2 1.2 4 1 .1 .4 1 0 24 21 45 0 0 0 1.1 1.4 3 0
IOVF USAGE SUMMARY
UOW'S USING IOVF: NO.: 48 %UOW'S: 74%
NO. IOVF CI'S USED: AVG: 1.89 SDEV : .94 MAX: 4 MIN: 1
AVAILABLE IOVF CI'S: NO.: 57 %CI'S: 38%
In these sections, check for the following information:
For UOWs that use IOVF, determine
if any free space is available in the DOVF. Refer to the threshold
values that you set for data elements DB_PCT_BYTES_FS_DOVF and DB_PCT_BYTES_FS_IOVF
(in rule IBM®.DEDB_FS.60) to
determine if free space in DOVF and IOVF is being used efficiently.
If free space is available in the
DOVF of the UOW, and if the IOVF is being used by the UOW, the space
in the DOVF might not be used efficiently or the free space might
need to be reorganized.
IOVF should not be used
if a sufficient amount of free space is available in the DOVF section
of most UOWs.
In the DOVF usage summary section, check the value in
the UOW'S USING DOVF field. Refer to the threshold values that you
set for data element DB_PCT_NUM_UOW_USE_DOVF (in rule IBM.DEDB_OVERFLOW.10) to determine if the percentage
of UOWs that use the DOVF section is low enough.
The
percentage of UOWs that use DOVF sections should not be high.
In the IOVF usage summary section, check the
value in the UOW'S USING IOVF field. Refer to the threshold values
that you set for data element DB_PCT_NUM_UOW_USE_IOVF (in rule IBM.DEDB_OVERFLOW.20) or DB_NUM_UOW_USE_IOVF
(in rule IBM.DEDB_OVERFLOW.30)
to determine if the percentage or the number of UOWs that use the
IOVF section is low enough.
The values should be zero
for those areas that are heavily accessed and that need high performance.
In the IOVF usage summary section, check the values
in the NO. IOVF CI'S USED field. Refer to the threshold values that
you set for data elements DB_AVG_NUM_IOVFCI_BY_UOW (in rule IBM.DEDB_OVERFLOW.40) and DB_MAX_NUM_IOVFCI_BY_UOW
(in rule IBM.DEDB_OVERFLOW.50)
to determine if the average and maximum use of IOVF CIs per UOW are
low enough.
The values should be zero for those areas
that are heavily accessed and that need high performance.
The DOVF and IOVF sections also provide information about
whether skewed distribution of overflow exists among UOWs.
Optional: Analyze free space utilization and
overflow at UOW level.
To obtain more information about
free space utilization at UOW level, especially when you identify
skewed distribution of overflow among UOWs, generate and analyze the
UOW report.
Summarize the observation of Freespace Analysis
report.
First, determine if the free space
of the area needs to be reorganized. Free space reorganization is
recommended if one or both of the following conditions are observed:
Free space elements are fragmented, and the percentage of FSEs
with sizes that are smaller than the sizes of segments to be added
has been increased.
The total size of free space in the CIs is sufficient,
but there are numerous references to other sections of the area.
Next, determine if the areas need to be expanded
based on your analysis of the free space availability in Step 1.
You might need to expand the areas if the packing density of RAA BASE is high
(based on your criteria) and the size of free space in both DOVF and
IOVF has fallen below the predetermined threshold that is set for
each section.
You might need to expand the SDEP part
if the amount of free space has fallen below a threshold value for
the SDEP free space.
The packing density of RAA BASE is the
value that shows the percentage of bytes that are used by segment
data compared to the total bytes of all the allocated RAP CIs in the RAA BASE (here,
total bytes do not include the bytes that are used by VSAM and IMS control data). You can calculate
the packing density by using the following formula:
100 - the percentage of free space in RAA BASE
where the
percentage of free space in RAA BASE is the value
that is shown in the Overview section of the Freespace Analysis report
(See Step 1).
What to do next
If the only exceptions that
you received are related to the overflow usage and free space availability,
and if you determined that free space needs to be reorganized, follow
the instructions in Planning free space reorganization and usage monitoring to
reorganize free space and to review the reorganization schedule.
If
you received other exceptions that are not related to free space availability,
and you determined that free space does not need to be reorganized,
continue with the steps in Understanding the status of DEDB areas.
If you received other exceptions that are not related to
free space availability, and if you determined that free space needs
to be reorganized and the area needs to be expanded, consider reorganizing
free space before working on other exceptions. Because the exceptions
are interrelated, free space reorganization might reduce the number
or lower the severity of exceptions. After reorganizing the areas,
run policy evaluation for the reorganized areas to determine how the
free space reorganization changed the situation by following the steps
in Understanding the status of DEDB areas.