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2-138 IBM Informix OnLine Database Server Administrator’s Guide

Structure of an Index Page

Figure 2-34 illustrates the root node page and the two leaf node pages that

result from a split after the root node ﬁlls.

Index Key Entries

Figure 2-34 includes index key entries on the root node index page that take

the following form:

■ A byte value followed by one address of a branch or leaf node page

■ Only a node address (the inﬁnity slot)

In addition, a third form is possible:

■ A byte value followed by a rowid, followed by two node addresses

(indicating a range of pages)

These three types of index key entries are described in the paragraphs that

follow. The entry types are illustrated in Figure 2-35 on page 2-139.

When thebyte value is followed by a singlebranch or leaf node address, the

index key entry indicates that only one rowid exists for this byte value. The

byte-addresspair entrypointstotheﬁrstdataslotonthe nodepagespeciﬁed

bytheaddress.Thenodepagecanbeeitheraleafnodepageorabranchnode

page.

Figure 2-34

After the root node

page ﬁlls, it splits

into two leaf nodes.

The inﬁnity slot

points to the node

that contains all

byte values greater

than the last value

actually stored at

this level. In this

example, the

inﬁnity slot points

to all values greater

than O’Brien.

KeyvaluesfromAlbertsontoMiller,

arranged in byte:rowid entries

KeyvaluesfromO’BrientoWatson,

arranged in byte:rowid entries

O’Brien: leaf node address

Page header

Inﬁnity slot

Albertson: leaf node address

Header

Root node

Leaf nodes

Horizontal

Link

1 2 ... 227 228 229 230 231 232 233 234 235 236 237 ... 701 702

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