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DCMT VARY DATABASE Usage

Attaching Independent Database I/O Read Drivers

You can attach an independent database I/O read driver to perform look-ahead reads of the database. This driver only works for run units that perform area sweeps under the central version.

This feature provides additional database tuning capabilities in the mixed online and batch environment.

General Considerations

The independent database I/O read driver has the following usage considerations:

• The read driver is only used for tasks that perform area sweeps under the central version.

  Note: For more information about look-ahead reads under local mode, see the System Operations Guide

• Use as few read drivers as possible. Because of the overhead, overuse of the read driver can degrade system performance.
• Use the WATCH DB IOD option of the OPER screen to monitor the read drivers.

  Note: For more information, see the section OPER WATCH DB".