6. DATA SOURCES › 6.6 I/O Measurements and Device Activity › 6.6.4 Device Activity And Utilization › 6.6.4.1 EXCP Segment Processing

6.6.4.1 EXCP Segment Processing

The CA MICS Batch and Operations Analyzer accumulates device
and data set allocation statistics by processing the EXCP
segments (or sections) of SMF records generated for batch job
steps, TSO sessions, started tasks, USS, and APPC/MVS ASCH
scheduled TPs (at the address space level).  The EXCP
segments of the SMF type 30 Common Address Space Work record
contain both dynamic and non-dynamic allocations.

The SMF type 30 record has a number of fields at the start of
the record that describe the segment types present, the
quantity of each segment type, and the length of each segment
type.  One of the segment types is the EXCP segment.  The
EXCP segment for an SMF type 30 record has the following
format:

                         EXCP SEGMENT
                  ---------------------------------
                  | DC UT DA DDN BLK BSZ DCT BLKZ |
                  ---------------------------------
     LENGTH BYTES    1  1  2  8   4   2   4    8

     Where DC   -    Device Class
           UT   -    Unit Type
           DA   -    Device Address
           DDN  -    DD Name used to access the data set
           BLK  -    Count of BLocKs issued for the device
           BSZ  -    Largest BlockSiZe of the data set
           DCT  -    Device Connect Time
           BLKZ -    Largest BLocKsiZe > 32760

Generally, each EXCP segment represents the complete activity
for one particular data set.  There are several exceptions to
this:

o When a data set spans multiple volumes, there will be an
  EXCP segment for each unique device address that the
  data set occupies.

o The SMF EXCP device activity is summarized by ddname and
  device address into a single EXCP segment before writing
  the segment to the SMF interval, step end, or job end
  record.  This means that repeated dynamic allocation and
  unallocation of different data sets using the same
  ddname and device address will result in a single EXCP
  segment representing multiple data sets.

o The SYS1.PARMLIB(SMFPRMxx) keyword DDCONS may be set to
  (NO) to prevent EXCP segment consolidation at the
  termination of a step.  This will cause individual EXCP
  segments to be written to the SMF record even when the same
  ddname and device address are used in multiple dynamic
  allocations and unallocations.

o The same data set may be allocated with different DDs,
  resulting in multiple EXCP segments.

o EXCP segments may be suppressed for DB2 started tasks to
  improve performance.

When the number of EXCP segments causes the record length to
exceed 32,756 bytes, SMF writes continuation type 30 records.
With continuation records, CA MICS outputs each EXCP segment
to a temporary data set for later summarization and inclusion
into the CA MICS files.

CA MICS will process a single SMF type 30 record with an
assembly language program that builds a device address table.

The DETAIL timespan BATWDA observations are derived by
summarizing the information in the EXCP segments by unique
device address.

The step or interval level Device Allocations data elements
are derived by summing the number of unique device addresses
found in the EXCP segments by Device Class.

The step or interval level Data Set Allocations data
elements are derived by summing the number of EXCP segments
by Device Class.