IBM 000-8697 Manual Do Utilizador

IBM Informix OnLine Database Server Administrator’s Guide

As administrator, attempt to follow as closely as possible the guidelines for
disk layout, blobpage sizing, and user education. As part of your daily
routine, monitor OnLine activity to become familiar with what can be
considered normal operation. (Refer to

monitoring, pay particular attention to several fields that could indicate a
need for tuning. The field values that might indicate a need for tuning are
listed here, along with a cross-reference to direct you to the appropriate
tuning discussion in this chapter.

Use the fields that report read- and write-caching percentages to indicate a
possible need for tuning.

■

The cached-read percentage refers to the number of reads done from
memory compared to the number of reads done from disk.

■

The cached-write percentage refers to the percentage of writes that are
performed to the shared-memory buffer compared to the number of
writes to disk.

These caching percentages are reported by the

DB-M

onitor Status menu,

Profile option or as part of the tbstat -p or tbstat -P output: %

cached

is the

cached percentage. The %

cached

field appears twice in both the

DB-M

onitor

and tbstat display.

If you use

DB-M

onitor, the cached-read percentage is the third field on the top

row of statistics. The cached-write percentage is the left-most field on the top
row, which is also labelled %

cached

.

If you use tbstat -p or tbstat -P, the cached-read percentage is the first occur-
rence of the field %

cached

. The cached-write percentage is the second

occurrence of the field %

cached

.

If the cached-read percentage is less than 95 percent or the cached-write
percentage is less than 82 percent, you might want to consider retuning.

Refer to

 for more details about using these fields to adjust the

number of shared-memory buffers.