Installation guide

22
Appendix
Oracle Advanced Compression
Many customers are looking for solutions that provide a means for reducing the size of their rapidly
growing databases without negatively affecting their end user performance. Oracle 11gR2 offers
integrated database compression to address this requirement.
We often think of compression as being a trade-off between performance and storage: compression
reduces the amount of storage required, but the overhead of compressing and decompressing makes
things slower. However, while there is always some CPU overhead involved in compression the effect
on table scan I/O can be favorable, since if a table is reduced in size it will require fewer I/O
operations to read it.
Prior to 11g, table compression could only be achieved when the table was created, rebuilt or when
using direct load operations. However, in 11gR2, the Advanced Compression option allows data to
be compressed when manipulated by standard DML (Data Manipulation Language). The data
compression feature in Oracle 11gR2 Enterprise Edition reduces the size of tables and indexes while
providing full row level locking for updates. There are two types of compression.
1. Row compression enables storing fixed-length data types in a variable-length storage format.
2. Page compression is a superset of row compression. It minimizes the storage of redundant data on
the page by storing commonly-occurring byte patterns on the page once, and then referencing
these values for respective columns.
Oracle’s Advanced Compression offers three distinct levels: low, medium, and high. HP and Oracle
recommend using the “low” method for best overall OLTP workload performance when data
compression is desired. Oracle has provided a compression algorithm specifically designed to work
with OLTP type workloads. This recommendation is based upon tests performed by HP and Oracle on
industrial-standard x86 hardware (see the reference at the end of this document). Users may wish to
evaluate other compression options to determine if the “medium” or “high” setting offers superior
performance for their specific workload.
As one would expect, Oracle Advanced Data Compression was very effective at reducing disk
utilization of traditional storage arrays. The result was improved data transfer from storage into the
database instance for processing and reduced I/O wait overhead. Testing conducted by HP’s Oracle
Alliances team showed that Advanced Data Compression scaled linearly across the full range of CPU
cores on HP 8-socket servers. All indications are that data compression will have an even greater
positive impact on performance with the VMA series Memory Array solutions.