IBM 000-8697 Manual Do Utilizador

IBM Informix OnLine Database Server Administrator’s Guide

Familiarize yourself with the definition of a checkpoint, and with the events
that happen during a checkpoint, before you begin this section. Refer to
pages

 and

 for background information.

The frequency of checkpoints and their duration affects OnLine performance.
Since OnLine restricts all database server processes from entering a critical
section during a checkpoint, frequent checkpoints might appear to lower
performance because user processing might be interrupted.

Your ability to tune the page-cleaning parameters means that you need not
rely solely on checkpoints to keep the shared-memory buffer pool clean. If
you wish, you can specify the page-cleaning parameters so that idle writes
maintain an adequate supply of free and/or unmodified page buffers, and
checkpoints are needed less frequently. (However, this might result in less-
than-peak performance. Refer to

for an explanation of why relying

on checkpoints to flush the shared-memory buffer pool might result in the
greatest overall performance.)

The decision to configure OnLine for less-frequent checkpoints implies two
tradeoffs:

■

You are liable to experience a longer fast-recovery time after an
operating system failure. The longer fast-recovery time is a conse-
quence of the larger physical log and the increased number of logical
log entries that are written between checkpoints.

■

The larger physical log requires more space on disk.