2-138 IBM Informix OnLine Database Server Administrator’s Guide
Structure of an Index Page
Figure2-34 illustrates the root node page and the two leaf node pages that
result from a split after the root node fills.
Index Key EntriesFigure2-34 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 inFigure 2-35 on page 2-139.
Whenthe byte value is followed by a single branch or leaf node address, the
index key entry indicates that only one rowid exists for this byte value. The
byte-addresspair entry points to the first data slot on the node page specified
bythe address. The node page can be either a leaf node page or a branch node
page.
Figure2-34
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.
Keyvalues fromAlbertsonto Miller,
arranged inbyte:rowid entries Keyvalues fromO’Briento Watson,
arranged inbyte:rowid entries
O’Brien: leaf node address
Page header
Infinity slot
Albertson: leaf node address
Header Header
Root node
Leaf nodes
Horizontal
Link