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Oracle Tips by Burleson |
OCP Instructors Guide for
Oracle DBA Certification
Chapter 5 - Oracle Database
Objects
Space Utilization for
Parallel Table Creates
CREATE TABLE test2 AS SELECT * FROM test1 STORAGE (INITIAL 2047M
NEXT 500M... PARALLEL 4;
The above statement would create a table that
has 4 extents with each extent being 2047M in size.
Index-only Tables
Oracle8 allowed you to define an index-only
table (see Figure 6) that keeps data sorted on the primary key.
Oracle stores the table rows in a B-tree index built on the primary
key. The B-tree index contains both the key value and the key
value’s corresponding row data.
Image 6: Index-only tables.
Index-only tables increase the performance of
SQL statements by providing faster access to table data for queries
that use the key value for exact value searches. Index-only tables
also increase performance by eliminating the index to table I/O
associated with conventional B-Tree index structures.
The first implementation of index-only tables
contained many restrictions on their implementation and usage. One
example is that secondary indexes were not allowed to be built on
index-only tables in Oracle8. Oracle removed restrictions and
enhanced index-only functionality with each subsequent release. It
is important that the DBA check the Oracle administrator’s guide for
their release to determine how to correctly administer index-only
tables.
The above text is
an excerpt from:
OCP Instructors Guide for Oracle DBA Certification
A Study Guide to Advanced Oracle Certified Professional Database
Administration Techniques
ISBN 0-9744355-3-8
by Christopher T. Foot
http://www.rampant-books.com/book_2003_2_OCP_print.htm
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