Fast Path EXEC parameters in DBCTL

Use Fast Path EXEC parameters to specify database buffer sizes and specify DEDB options in a DBCTL environment.

The PARM1= and PARM2= positional parameters for the control region's EXEC statement that can be used to specify the Fast Path parameters in a DBCTL region are shown below.

Table 1. Categories and purpose of Fast Path control region parameters for DBCTL
Category	Parameter	Purpose
Database buffer sizes	BSIZ	Specify the common size of a buffer
	DBBF	Specify the maximum number of buffers
	DBFX	Specify system buffer allocation
DEDB options	OTHR	Specify the number of DEDB updates that can be concurrently waiting for I/O after sync point
DEDB options	LGNR	Specify the maximum DEDB buffer alterations before CI logging
EPCB	EPCB	Specify the size of the EPCB pool

When an emergency restart is performed, the values specified for the EXEC parameters BSIZ, DBBF, OTHR, and LGNR must remain unchanged from the last normal start. These values are used when reestablishing buffer contents from checkpoint records.

Database buffer sizes

Using the DBBF and BSIZ parameters, you manually specify the total buffers available for the IMS online system's processing of DEDB activity. Dependent regions then claim portions of this allocation. Use DBFX to specify additional buffers (not separate pools) that are set aside and page-fixed at when the control region is initialized. These buffers allow for asynchronous processing.

If you prefer to have IMS automatically manage Fast Path buffer pools, enable the Fast Path 64-bit buffer manager using the DFSDFxxx PROCLIB member.

DEDB options

The OTHR parameter specifies the number of asynchronous output threads. It allows you to revise the estimate of DEDB updates occupying buffer space while waiting to be committed to the area data sets after sync point logging.

The OTHR= parameter can have any value from 1 to 32,767. If a value is not specified, the default is 255. If 0 or a value greater than 32767 is specified, the default is 2. If a value from 1 to 32767 is specified, the specified value is used.

The LGNR parameter determines a maximum for the number of DEDB alterations made in a buffer that are individually logged. Above that number, the whole control interval (CI) is logged. The default value is 7, and you can specify a number from 7 to 99. If the application program is using large CIs, the LGNR value can be increased to economize on the system log activity.