Fast Path EXEC parameters in DCCTL or DB/DC

Use Fast Path EXEC parameters to specify database buffer sizes and specify DEDB options in a DCCTL or IMS DB/DC environment.

Note: Although the DCCTL environment does not support Fast Path databases, it does support Fast Path processing and transactions.

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

Table 1. Categories and purpose of Fast Path control region parameters for DCCTL and DB/DC
Category Parameter Purpose
MSDB load MSDB Specify the DBFMSDBx suffix
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
LGNR Specify the maximum DEDB buffer alterations before CI logging
EPCB EPCB Specify the size of the EPCB pool
EMHL EMHL Specify the size of the EMHL buffer

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

MSDB loading

The MSDB parameter enables you to control which MSDBs must be loaded for the current online session and how many segments each MSDB requires. The parameter is generated with a null value, implying that the MSDBs are loaded directly from a Fast Path system data set. You specify a one-character suffix that points to an IMS.PROCLIB member, DBFMSDBx, containing the detailed requirements.

If the MSDB requirements for an online session are a subset of the MSDBs, or if the number of segments for any MSDB is to be increased to reserve space for dynamic terminal-related MSDBs, you must coordinate the content of the DBFMSDBx member and the MSDB parameter value. The control statements in the DBFMSDBx member must explicitly name all MSDBs required to be loaded. The control statements also enable you to individually select MSDBs for page fixing.

LU 6.2 devices allow read-only access to dynamic MSDBs. LU 6.2 devices cannot access terminal-related MSDBs.

Terminals defined dynamically with ETO are not available to terminal-related MSDBs.

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. You can revise the estimate of DEDB updates that occupies buffer space while they are 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 number of individually logged DEDB alterations made in a buffer. 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.