Apress.Expert.Oracle.Database.Architecture.9i.and.10g.Programming.Techniques.and.Solutions.Sep.2005

CHAPTER 10 ■ DATABASE TABLES 339
• A table can have a virtually unlimited number of rows, although you will hit other limits
that prevent this from happening. For example, typically a tablespace can have at most
1,022 files (although there are new BIGFILE tablespaces in Oracle 10g that will get you
beyond these file size limits, too). Say you have 32GB files—that is to say, 32,704GB
per tablespace. This would be 2,143,289,344 blocks, each of which is 16KB in size. You
might be able to fit 160 rows of between 80 to 100 bytes per block. This would give you
342,926,295,040 rows. If you partition the table, though, you can easily multiply this
number many times. For example, consider a table with 1,024 hash partitions—that
would be 1024 ✕ 342,926,295,040 rows. There are limits, but you’ll hit other practical
limitations before even coming close to these figures.
• A table can have as many indexes as there are permutations of columns (and permutations
of functions on those columns). With the advent of function-based indexes, the
true number of indexes you could create theoretically becomes infinite! Once again,
however, practical restrictions will limit the actual number of indexes you will create
and maintain.
• There is no limit to the number of tables you may have, even within a single database.
Yet again, practical limits will keep this number within reasonable bounds. You will not
have millions of tables (this many is impracticable to create and manage), but you
may have thousands of tables.
In the next section, we’ll look at some of the parameters and terminology relevant to
tables. After that, we’ll jump into a discussion of the basic heap-organized table, and then
move on to examine the other types.
Terminology
In this section, we will cover the various storage parameters and terminology associated with
tables. Not all parameters are used for every table type. For example, the PCTUSED parameter is
not meaningful in the context of an IOT. We’ll cover the relevant parameters as part of the discussion
of each individual table type. The goal is to introduce the terms and define them. As
appropriate, more information on using specific parameters is covered in subsequent sections.
Segment
A segment in Oracle is an object that consumes storage on disk. While there are many segment
types, the most popular are as follows:
• Cluster: This segment type is capable of storing tables. There are two types of clusters:
B*Tree and hash. Clusters are commonly used to store related data from multiple tables
“prejoined” on the same database block and to store related information from a single
table together. The term “cluster” refers to this segment’s ability to cluster related information
physically together.
• Table: A table segment holds data for a database table and is perhaps the most common
segment type used in conjunction with an index segment.