5-20 IBM Informix OnLine Database Server Administrator’s Guide

Checkpoint Frequency

Checkpoint Frequency
Familiarizeyourself with the definition of a checkpoint, and with the events
that happen during a checkpoint, before you begin this section. Refer to
pagespage 2-70 and page 2-72 for background information.

Performance Tradeoffs

Thefrequency 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-peakperformance. Refer to page 5-18for 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-
quenceof 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.