Control statements that affect performance
Use the HSSRCABP control statements to allocate more buffers to tune the performance of your job. Some control statements that are specified in the HSSROPT data set can also affect the performance of CAB.
HSSRCABP control statements
HSSRCABP data set contains the CAB control statements that are used to change CAB buffering parameters and options for a specified data set or for a specified group of data sets. The statements make it possible to override the default values of the CAB parameters. The following table lists the HSSRCABP control statements.
|CABDD||This control statement defines a data set or a group of data sets to which the succeeding CAB control statements apply.|
|OCCURRENCE||This optional control statement specifies the HSSR PCB to which the specifications of the control statement set apply. It is used when multiple HSSR PCBs refer to the same database.|
|RANSIZE||This optional control statement specifies the size of a range,
which is the fixed number of ESDS CIs, OSAM LDS CIs, or OSAM blocks read together in one chained
sequential I/O operation.
The default value for RANSIZE is determined from the characteristics of each database data set; the default value is determined as follows:
This default is efficient for relatively well organized databases.
A RANSIZE value smaller than the default can be specified to reduce the buffer space. (In this case, the REFT4 parameter value, if it is coded, must also be reduced.)
|NBRSRAN||This optional control statement specifies the number
of whole ranges to be buffer-resident for look-aside buffering.
The NBRSRAN parameter affects the number of successful look-aside operations, as well as buffer space.
With well-organized databases, NBRSRAN can be reduced to the minimum value of 3 (because look-aside operations are less important with well organized databases) to reduce the buffer space.
With disorganized databases, increasing NBRSRAN can sometimes increase the number of successful look-aside operations. This decreases the number of direct and chained sequential I/Os.
|NBRDBUF||This optional control statement specifies the number of single blocks or CIs read with direct I/O to be buffer-resident for look-aside buffering.|
|OVERFLOW||This optional control statement affects the buffering
of the prime data set group of an HDAM or PHDAM database and describes
how the overflow area should be buffered.
The OVERFLOW parameter affects the buffering of HDAM and PHDAM databases. If a large number of I/O operations are performed in the overflow area, either the OVERFLOW CAB option (default) or the OVERFLOW SHR option is recommended, because either of them allows chained sequential I/O in the overflow area. Note that the OVERFLOW CAB option requires more buffer space than OVERFLOW SHR.
The OVERFLOW BB is reasonable if only a few I/O operations are performed in the overflow area. However, it does not allow chained sequential I/O in the overflow area.
|REFT4||This optional control statement is used as a reference
threshold value to help determine whether chained sequential I/O or
direct I/O should be performed.
The default value of REFT4 equals to that of RANSIZE. This value can be decreased or increased, to regulate the number of direct and chained sequential I/O operations.
This parameter does not affect the number of buffers to be allocated by CAB.
|INTER||This optional control statement activates the CAB inter-PCB look-aside, which enables CAB to attempt to find a requested RBA within buffers of other HSSR PCBs that refer to the same database.|
|PARTPROC||This optional control statement, valid only for
HALDB, specifies the access intent for the database or the databases
specified on the statement.
For a HALDB, CAB buffers are shared among data sets that belong to the same data set group. If only one partition is accessed at a time, as in the unload utilities such as FABHURG1 or FABHFSU utility, you do not need to use this control statement. If more than one partition is accessed randomly, you must specify the number of partitions that are accessed at a time.
For the detailed description of PARTPROC statement and the buffer sharing for HALDB, refer to CAB buffer sharing for HALDB.
HSSROPT control statements
This input data set provides control statements that affect CAB buffering. The following table shows a brief review of the HSSROPT control statements that you might want to consider using with CAB. For a detailed description of these control statements, see Options for HSSR Engine.
|BUTR||This optional control statement activates a trace of CAB buffering activities.
The trace is written to the data set defined by the HSSRBUTR DD statement. This data set is used as
input to FABHBSIM to simulate CAB buffering in order to tune CAB buffers.
The buffer trace is not taken for HALDBs.
|NOFIX||This optional control statement prevents page-fixing. Since a noticeable amount of paging might occur when CAB buffers are not page-fixed, this statement is usually omitted.|
|NOVSAMOPT||This optional control statement prevents CAB from using the default read-ahead threshold value used by VSAM.|