IBM 000-8697 Instrukcja Użytkownika Pobierz pdf (Strona 454)

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5-14 IBM Informix OnLine Database Server Administrator’s Guide

Shared-Memory Resources

Important: Low caching percentages might reﬂect improperly tuned page-cleaning

parameters. If increasing the value of BUFFERS does not increase the caching

percentages, refer to page 5-17.

Refer to page 3-92 for more details about how to change the value of

BUFFERS.

Shared-Memory Resources

Ifdatabaseserverprocessesarewaitingforalimitednumbershared-memory

resources, you can improve performance by allocating more of the needed

resource. You can eliminate waiting for an entry in the locks, tblspaces, or

users table by increasing the value of TBLSPACES, LOCKS, or USERS in the

conﬁguration ﬁle. However, each increase also increases the size of shared

memory, which is rarely an unlimited resource. You must always weigh the

positive effect of increasing OnLine shared memory against any negative

effectsthatmight be experiencedbyotherapplications running onyour host

machine.

When Is Tuning Necessary?

Look at the proﬁle of OnLine activity. A low positive number in any one of

the three ﬁelds ovtbls, ovlock, or ovuser does not necessarily indicate a

need for tuning. A high value is more indicative of a need for more buffers.

If the value of ovbuff exceeds 50 or 60 within a 24-hour period, begin to

monitor the ﬁeld over ﬁxed time intervals. (Use tbstat -z to set all proﬁle

statistics to 0.) If it appears that OnLine requests consistently exceed the

BUFFERS value, you should attempt to tune your conﬁguration.

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