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2-136 IBM Informix OnLine Database Server Administrator’s Guide
Structure of an Index Page
Figure 2-33 represents this initial phase of index storage. (Refer to page 2-121
for a general explanation of the function of the slot table. Refer to page 2-121
for more information about the page-header and page-ending timestamp
pair.)
Leaf Node Pages
When the first index page becomes full, the page splits into three pages: one
root node page and two leaf node pages. The root node page now contains
two index key value entries. Each entry is a pointer to the first data that
appears on one of the leaf pages.
In addition, the root page now includes a third entry called the infinity slot.
The infinity slot points to the node that contains all byte values greater than
the last value actually stored at this level. One infinity slot exists at the root
node level and at each branch node level. (Refer to page 2-138 for more infor-
mation about the root node infinity slot.)
Horizontal linksexist between the two leaf pages. All nodes on the same level
are horizontally linked, branch-to-branch or leaf-to-leaf. The links are imple-
mented as pointers to the next page. These pointers, which are stored in the
branch or leaf page header, facilitate OnLine sequential reads.
Figure 2-33
The first index page
fills with index key
values and slot
table entries until
there is no room for
an additional index
entry on the page.
At this point, the
first page splits into
three pages.
Page header
Index key values
Slot table entries
Timestamp