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5-20 IBM Informix OnLine Database Server Administrator’s Guide
Checkpoint Frequency
Checkpoint Frequency
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 page 2-70 and page 2-72 for background information.
Performance Tradeoffs
The frequency of checkpoints and theirduration 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 page 5-18 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.