|
CICS
TS uses a mechanism to limit concurrent execution of transactions in a
CICS TS partition. Transaction class definitions are used to limit the
maximum number of transactions that can execute concurrently in a
specific class. It is also used to limit the total number of
transactions that can be queued up waiting to execute in a specific
class. If the values defined for transaction classes are coded too low,
CICS task performance can suffer.
The
definition of transaction classes in CICS TS has changed from those in
CICS/VSE. In CICS/VSE the SIT CMXT parameter was used to define the
maximum number of tasks that could execute concurrently in a total of
ten transaction classes numbered 1 through 10. A transaction was
assigned to a specific class by coding a transaction class number in the
TCLASS parameter of the PCT or RDO transaction definition.
In
CICS TS the RDO DEFINE TRANCLASS command is used to define transaction
classes and replaces the CICS/VSE CMXT parameter. Transaction classes
are now defined with names rather than numbers thus more than ten
transaction classes can be defined. The TRANCLASS parameter in the RDO
DEFINE TRANSACTION command replaces the TCLASS parameter from CICS/VSE.
For
migration from CICS/VSE, IBM supplies default transaction classes named
DFHTCL01 through DFHTCL10 to replace the ten numeric classes in CICS/VSE.
If the TCLASS parameter was used in CICS/VSE, it is migrated to one of
the supplied transaction class names corresponding to the numeric value
in the TCLASS parameter.
The
MAXACTIVE parameter in the DEFINE TRANCLASS command is used to limit the
maximum number of concurrent tasks in that class. The IBM supplied
value for each of the ten default classes is one. If you were using
values other than one in your CMXT parameter in CICS/VSE, then you will
need to copy the IBM supplied definitions to your own transaction class
group and modify the values to match your CICS/VSE CMXT values.
CICS
TS also provides a new parameter, PURGETHRESH, on the transaction class
definition to limit the number of tasks that can be queue up waiting to
execute in a specific class. If a new transaction is invoked in that
class and the value of the PURGETHRESH parameter is reached then that
new transaction request will be abended with an AKCC abend. A
PURGETHRESH value of zero will cause the CICS TS transaction class
mechanism to work the same as CICS/VSE, i.e. no limit on the number of
tasks that can be queued for a transaction class.
CICS
TS statistics can be used to monitor transaction class settings. The
statistics show number of times the limit was reached for each
transaction class defined in the CICS partition and how many
transactions were queued up waiting. Ideally, this statistic should be
zero, however, some transactions may need to be limited in terms of how
many can execute concurrent because of the demands they put on system
resources such as processor utilization, virtual storage or I/O
subsystems.
|
Tell
us what you want to know in iTips and give suggestions on topics - send
an email to