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Oracle Tips by Burleson |
OCP Instructors Guide for
Oracle DBA Certification
Chapter 5 - Oracle Database
Objects
Figure 4: Index keys in a global index.
Oracle8i – Hash and
Range/Hash Composite Partitioning
Oracle8i enhanced the Oracle database’s
partitioning feature by providing two new partitioning techniques,
hash and range/hash composite.
Hash Partitioning
Hash partitioning allows data to be evenly
striped across devices. Hash partitioning uses a hashing algorithm
on the partitioning columns to determine row placement in the
tablespaces. The more unique the key values are, the more efficient
the hashing algorithm will be. In general, the hash-partitioning
key should be unique or near unique.
Hash partitioning attempts to evenly divide
data among all available partitions. There is no way for the
administrator to logically group data together in a partition. As a
result, hash partitioning prohibits "partition pruning" from
occurring. Hash partitioning also prevents "rolling window"
operations from occurring. Rolling windows allow administrators to
roll off data that is no longer needed.
Combining Range and Hash
Partitioning – Range/Hash Composite Partitioning
Range/hash composite partitioning combines the
best of both approaches. A range of values first partitions data
then each partition is sub-partitioned into several hash partitions.
This provides administrators with the ability to provide customized
partitioning per application. The user specifies ranges of values
for the primary partitions of the table or index then specifies a
number of hash subpartitions.
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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