IDX_RA_THRESHOLD

onconfig.std
value

None

if not present

IDX_RA_PAGES/2

units

Number of index pages

range of values

0 through (IDX_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 IDX_RA_PAGES and IDX_RA_THRESHOLD in your IBM Informix: Performance Guide

The IDX_RA_THRESHOLD parameter is used with IDX_RA_PAGES when the database server reads during sequential scans of index records. IDX_RA_THRESHOLD specifies the read-ahead threshold; that is, the number of unprocessed index pages in memory that signals the database server to perform the next read-ahead.

If the value of IDX_RA_THRESHOLD is greater than the value of IDX_RA_PAGES, then IDX_RA_THRESHOLD has a value of IDX_RA_PAGES/2.

Use a larger IDX_RA_PAGES value if the range of index values scanned is big. Specifying values that are too large for IDX_RA_PAGES and IDX_RA_THRESHOLD can result in excessive buffer-caching activity.

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

% onutil
1> SET IDX_RA_THRESHOLD 16;