
5-4 IBM Informix OnLine Database Server Administrator’s Guide
Disk Layout
Performance-tuning issues are addressed as six topics in this chapter:
■ When is tuning needed? (page 5-10)
■ Shared-memory buffers (page 5-13)
■ Shared-memory resources (page 5-14)
■ Log buffer size (page 5-15)
■ Page-cleaner parameters (page 5-17)
■ Checkpoint frequency (page 5-20)
IfyouarerunningOnLineonamultiprocessormachine,twomultiprocessor-
specific features are available:
■ Psort parallel-process sorting package (page 5-22)
■ SPINCNT configuration parameter (page 5-24)
Disk Layout
PossiblythegreatestgainsinOnLine performance accrue fromstrategic disk
layout. It is not a simple matter to correct improper or poorly planned disk
layout after you have configured and initialized OnLine disk space. For this
reason, disk layout issues are addressed in Chapter 1 as part of your initial
configuration planning. Each time that you create a blobspace or dbspace,
you should review the basic principles described on page 1-43.
OnLine has an improved method of constructing indexes. Data is sorted
beforetheindexisbuilt.Thesortusesspacein/tmp(alltemporarytablesand
indexesarebuildinthe rootdbspace).The use of /tmp decreasesastheindex
is built so that, as the index grows, the need for sort space decreases.
You can improveperformancebystrategicplacement of the UNIXdirectories
thatOnLineusesforitsintermediate,sortwrites.Youcandefinethedirectory
that should be used for this purpose by defining the environment variable
DBTEMP. If DBTEMP is not set, OnLine uses the /tmp directory.
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