RA_THRESHOLD

onconfig.std
value

None

if not present

RA_PAGES/2

units

Number of data pages

range of values

0 through (RA_PAGES - 1)

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 RA_PAGES and RA_THRESHOLD in your IBM Informix: Performance Guide

RA_THRESHOLD is used with RA_PAGES when the database server reads during sequential scans of data records. RA_THRESHOLD specifies the read-ahead threshold; that is, the number of unprocessed data pages in memory that signals the database server to perform the next read-ahead.

If the value of RA_THRESHOLD is greater than the value of RA_PAGES, RA_THRESHOLD has a value of RA_PAGES/2.

Specifying values that are too large for RA_PAGES and RA_THRESHOLD can result in excessive buffer-caching activity.

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

%onutil
SET RA_THRESHOLD 12;