rdisp/ROLL_SHM: Roll Buffer Size

Use

This value specifies the size of the roll buffer in 8 KB blocks.

The roll buffer functions as the cache for the roll file. For a fast change of context to occur, the roll areas of all user contexts should find space in the roll buffer (approximately 1 MB for each user).

Goal:

Minimum time for a context change

Integration

rdisp/ROLL_SHM : Buffered data is in the shared memory; accessing this data here is much faster than accessing a file.

For technical reasons, the roll buffer size must be at least 10% of the roll file size (parameter rdisp/ROLL_MAXFS: Maximum roll file size).

Activities

Unit: 8 KB

Default value: 0

Recommended value: UNIX: 8000, IBM AS/400: 0, under Microsoft Windows NT 128 blocks (1 MB)

Unless the Tune summary in the CCMS (Transaction ST02) (under Monitoring the Memory Management System) specifies that a larger roll buffer is required, do not set a value larger than 12500 (100 MB).

Absolute upper limit: 250000 blocks (2 GB) for special applications (file system must be large enough)

You can find the values in the configuration examples (Contents button). For more information on Windows NT, see Parameter Overview for Windows NT.

Changes: The customer can make changes.