IDX_RA_PAGES

onconfig.std
value

None

if not present

4 if MULTIPROCESSOR is 0 8 if MULTIPROCESSOR is 1

units

Number of index pages

range of values

IDX_RA_THRESHOLD through BUFFERS

takes effect

When shared memory is initialized

utilities

onutil

refer to

The following material:

• Configuring the database server to read-ahead in the shared-memory chapter of the IBM Informix: Administrator's Guide
• Calculating IDX_RA_PAGES and IDX_RA_THRESHOLD in your IBM Informix: Performance Guide

The IDX_RA_PAGES parameter specifies the number of disk pages to attempt to read ahead during sequential scans of index records. Read-ahead can greatly speed database processing by compensating for the slowness of I/O processing relative to the speed of CPU processing.

This parameter works with the IDX_RA_THRESHOLD parameter. Use a larger IDX_RA_PAGES value if the range of index values scanned is big. Specifying values that are too large can result in excessive buffer-caching activity. For more information on calculating IDX_RA_PAGES and IDX_RA_THRESHOLD, see your IBM Informix: Performance Guide.

To modify the IDX_RA_PAGES parameter dynamically, use the onutil SET command. Example:

% onutil
1> SET IDX_RA_PAGES 32;