Recovery-related EXEC parameters for the control region

The EXEC parameters that you can use to control the kind of recovery that is performed for the current system execution include DBRC=, DBRCNM=, QTU=, AND QTL=.

Note: The specifications of the ARC= and WADS= parameters are now in the LOGGER section of the DFSDFxxx PROCLIB member.

DBRC=

Batch and utility regions use the DFSIDEF0 module during initialization. The DFSIDEF0 module that is shipped in the ADFSSMPL library contains a batch and utility region default of DBRC=YES. This value is coded on the DFSIDEF macro.

You are not required to use the DFSIDEF0 module. If you do not use the module, or if the module cannot be loaded at initialization time, IMS defaults to DBRC=YES. Therefore, if DBRC is to be used for your batch and utility regions, then creating the DFSIDEF0 module is not required.

For online environments (DBCTL, DCCTL, or DB/DC), the only valid value is DBRC=YES.

For batch and utilities, you might want to change the default or current value for DBRC.

For batch and utilities, the default is DBRC=Y. To change the default value for DBRC, you can do either of the following:

Assemble and bind DFSIDEF0 into the IMS execution library; you can specify DBRC=Y, DBRC=N, or DBRC=FORCE. If you specify RMODE, you must specify RMODE=24 and AMODE=24
Override the value in a DFSPBxxx PROCLIB member. You can specify only DBRC=N or DBRC=Y.
To do this, you must define the RGSUF= parameter in your DLIBATCH or DBBBATCH procedure.

To change the current value for DBRC, override the value in JCL. You can specify only DBRC=N or DBRC=Y.

Sample JCL to assemble and bind the DFSIDEF0 module is shown below:

//ASSEMBLE EXEC PGM=ASMA90,PARM='NOOBJ,DECK'
//SYSLIB DD DSN=IMS.SDFSMAC,DISP=SHR
//SYSPUNCH DD DISP=OLD,DSN=IMS.OBJDSET(DFSIDEF0)
//SYSPRINT DD SYSOUT=*
//SYSUT1   DD UNIT=SYSDA,DISP=(,DELETE),SPACE=(CYL,(15,15))
//SYSIN    DD *
IDEF0    TITLE 'DFSIDEF0 - IMS INSTALLATION DEFAULTS BLOCK'
DFSIDEF0 CSECT
         SPACE 1
         DFSIDEF TYPE=BEGIN
         DFSIDEF TYPE=PARM,DBRC=YES
*****    DFSIDEF TYPE=PARM,DBRC=NO
*****    DFSIDEF TYPE=PARM,DBRC=FORCE
         DFSIDEF TYPE=END
         END   DFSIDEF0
//STEP1 EXEC PGM=IEWL,
//             PARM='SIZE=(880K,64K),NCAL,LET,REUS,XREF,LIST'
//SYSPRINT DD  SYSOUT=*
//SYSPUNCH DD DSN=IMS.OBJDSET,DISP=SHR
//SYSLMOD  DD DSN=IMS.SDFSRESL,DISP=SHR
//SYSUT1   DD UNIT=(SYSDA,SEP=(SYSLMOD,SYSPUNCH)),SPACE=(CYL,(10,1))
//SYSLIN   DD *
 INCLUDE SYSPUNCH(DFSIDEF0)
 NAME DFSIDEF0(R)

DBRCNM=

Specify a name (do not accept the default) for the start procedure for the DBRC region on the DBRCNM parameter. The default is a null parameter indicating a procedure name of DBRC. Also as part of your installation's recovery strategy, the AUTO parameter specifies whether to use automatic restart of the IMS online system. You need to override the generated default value (N) by specifying AUTO=Y if you plan to use automatic restart.

QTU= and QTL=

For a non-shared queues environment, the QTU and QTL parameters are associated with protection of the message queues. Use them to adjust the values in the message queue space notification exit routine (DFSQSPC0). Given the number of records reserved on each message queue data set for automatic shutdown (specified in system definition with the SHUTDWN parameter on the MSGQUEUE macro), a finite number of residual records are available for message use. The notification exit routine keeps track of the current level of utilization. If the usage exceeds the upper limit (expressed as a percentage of records used), the MTO is notified so that steps can be taken to reduce the backlog. The MTO is also notified if the usage falls below the lower limit.

For a shared queues environment, the QTU and QTL parameters are used to monitor the device relative record number (DRRN) in-use count. If the high threshold value is reached, a DFS2281I message is issued, and all messages retrieved from shared queues are put in an IWAIT state. When the DRRN in-use count becomes less than the low threshold value, a DFS2282I message is issued, and the messages in an IWAIT state are then posted.

The QTU and QTL values are one or two-digit percentages. QTU overrides the upper threshold value and QTL overrides the lower one (100 is allowed for QTU). Both upper and lower threshold values are generated with null values; the defaults are those of the IBM-supplied exit routine—75% and 60%, respectively. Unless your installation establishes its own exit routine to control the MTO notification, you should probably use these defaults. In the long term, you can tune them to fixed values based on the feedback from the statistics given in the /DISPLAY POOL command; enter this command during peak periods of activity.