Oracle Architecture - Oracle Essentials - page 42

This figure shows two tablespaces within an Oracle Database. When you create a new
table in this Oracle Database, you may place it in the DATA1 tablespace or the DATA2
tablespace. It will physically reside in one of the datafiles that make up the specified
tablespace.
Oracle's default tablespaces for all types of tables are locally managed tablespaces as of
Oracle Database 10 g Release 2. As the name implies, locally managed tablespaces are
typically more efficient, since the tracking of space in the tablespace is done locally,
rather than contending for space management information in the shared data dictio‐
nary. Locally managed tablespaces enable creation of bigfiletablespaces that can leverage
64-bit systems and their ability to manage ultra-large files.
Oracle9 i introduced the concept of Oracle Managed Files (OMFs), which enable your
database to automatically create, name, and delete, where appropriate, all the files that
make up your database. OMFs reduce the maintenance overhead of naming and track‐
ing the filenames for your database, as well as avoiding the problems that can result
from human errors in performing these tasks.
Oracle Databases can be deployed on up to 64,000 datafiles. Because a bigfiletablespace
can contain a file that is 1,024 times larger than a smallfiletablespace, and bigfiletables‐
paces have 32 KB block sizes on 64-bit operating systems, the Oracle Database can grow
to up to 8 exabytes in size (an exabyte is equivalent to a million terabytes). 1 The bigfi‐
letablespace is designed for use with Oracle's Automatic Storage Management (ASM),
other logical volume managers that support striping, and RAID. 2
Files of a database
There are three fundamental types of physical files that make up an Oracle Database:
• Control files
• Datafiles
• Redo logfiles
These three fundamental types represent the physical database itself. Figure 2-3 illus‐
trates the three types of files and their interrelationships.
1. The ultimate size of a bigfile depends on the limitations of the underlying operating system.
2. RAID stands for “redundant array of inexpensive disks” and is described in Chapter 7 .