Index organized tables reduce the total amount of space needed to store an
index and a table by eliminating the need to store the ROWID in the leaf page. But
index organized tables cannot use a UNIQUE constraint or be stored in a cluster. In
addition, index organized tables don??™t support distribution, replication, and partitioning
(covered in greater detail in other chapters), although IOTs can be used with
Oracle Streams for capturing and applying changes with Oracle Database 10g and
later releases.
There were a number of enhancements to index organized tables as of Oracle9i,
including a lifting of the restriction against the use of bitmap indexes as secondary
indexes for an IOT and the ability to create, rebuild, or coalesce secondary indexes
on an IOT. Oracle Database 10g continued this trend by allowing replication and all
types of partitioning for index organized tables, as well as providing other
enhancements.
Figure 4-1. A B*-tree index
Deal - ROWID
Howard - ROWID
Isis - ROWID
Adams
Brown
Culver
Deal
Howard
Isis
Jules
Klein
Main
Moss
Porter
Sikes
Sykes
Thomas
Topper
Vera
Wagner
Yanks
Davis
Jones
Smith
Turner
Turner>
Miller
Miller
Branch
blocks
Leaf
blocks
Detail of leaf node
94 | Chapter 4: Oracle Data Structures
Reverse key indexes
Reverse key indexes, as their name implies, automatically reverse the order of the
bytes in the key value stored in the index.
Pages:
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221