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Storage Structures

As shown in Figure 3-1, the physical schema objects are stored as segments in the database. Each segment can only be stored in a single tablespace and a tablespace can be made up of one or more datafiles. If a tablespace is running out of space, you can expand the datafiles it is made up of, or you can also add a new datafile to the tablespace. A datafile can only store data for a single tablespace.

A single tablespace can store data for multiple segments and in fact for several segment types. Segments from multiple schemas can also exist in the same tablespace. So, for example, table_a from schema1 and index_b from schema2 can both be implemented in the same tablespace. Oh and by the way, a tablespace can only store data for a single database.

The logical structures such as views and source code are stored in the Oracle catalog but are part of a schema. So, this means that the Oracle-supplied SH schema can contain all of the objects that it needs to run the entire application under its own schema name. This provides strong security and management benefits.

Progress Check Image

1. Name five areas that you will need to address as a DBA.

2. What is a schema and what does it contain?

3. Can a tablespace store more than one segment type?

4. Under which circumstances would you bother to start up the database in nomount mode?

CRITICAL SKILL 3.5
Operate Modes of an Oracle Database 10g

Oracle is a software package like many others that you may have used. However, when you run most programs, they run one and only one way. So when I open my accounting software, I run it the same way all the time. However, you have options

Progress Check Answers

1. As a DBA, you will need to address architecture, capacity planning, backup and recovery, and security and performance, among others.

2. A schema is a logical structure that contains objects like segments, views, procedures, functions, packages, triggers, user-defined objects, collection types, sequences, synonyms, and database links.

3. A single tablespace can store data for multiple segments and different segment types. Segments from multiple schemas can also exist in the same tablespace. So, for example, table_a from schema1 and index_b from schema2 can be implemented as two segments in the same tablespace.

4. When started in nomount mode, the parameter file is read and memory structures and processes are started for the instance. The database is not yet associated with the instance. You will use this in cases where you need to re-create the controlfile.

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0116-CRITICAL SKILL 3.5 Operate Modes of an Oracle Database 10<em>g</em>