Please refer to those
chapters for more information about RAID disk arrays. In addition, since Oracle
302 | Chapter 12: Oracle and Hardware Architecture
Database 10g, Automatic Storage Management (ASM) delivers much of the functionality
of a RAID array, such as striping and mirroring, with a collection of commodity
disks. ASM is further described in Chapter 5.
Oracle9i introduced table compression in the database as a means of decreasing disk
storage requirements primarily in data warehousing. Duplicate values in a data block
are eliminated because values that are duplicated are stored in a symbol table at the
beginning of the block, and all additional occurrences are replaced with a short
reference to the symbol table. Oracle Database 11g also features an Advanced
Compression Option for insert, update, and delete operations important in OLTP
operations. Data compression of 50 percent is commonly observed today. In addition
to reducing disk storage, compressed data can also be advantageous for
performance when it fits entirely into cache (instead of requiring disk access).
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