Installation guide

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.