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Lesson 1

Managing Large Objects (LOBs) and Memory

Large Objects (LOBs) were introduced in Oracle 7.0, which was released in 1992. LOBs are a set of data types that are designed to hold large amounts of data, such as text, images, and multimedia content. LOBs can be up to 4 GB in size, and they can be stored in the database or in external files.
Oracle 7.0 introduced four types of LOBs: BLOBs (Binary Large Objects), CLOBs (Character Large Objects), NCLOBs (National Character Large Objects), and BFILEs (Binary Files). BLOBs store binary data, such as images and audio files. CLOBs store character data, such as text and XML documents. NCLOBs store national character data, such as text in Unicode or UTF-8. BFILEs store data in external files.
LOBs are a powerful tool for storing large amounts of data in Oracle. They are used in a wide variety of applications, such as document management systems, content management systems, and multimedia applications.
Here is a table that summarizes the four types of LOBs:

LOB Type Data Type Description
BLOB Binary Stores binary data, such as images and audio files.
CLOB Character Stores character data, such as text and XML documents.
NCLOB National Character Stores national character data, such as text in Unicode or UTF-8.
BFILE Binary File Stores data in external files.
Large Objects, or LOBs, are data types designed to hold special types of information that take up a large amount of storage space. Oracle gives you several types of LOBs, each designed for a slightly different type of data, as well as some specific functionality designed to make your usage of LOBs more flexible and efficient.

Module Objectives

In this module, you will learn about LOBs and how to use them, including how to:
  1. Describe the different types of LOB data types
  2. Differentiate between the criteria for selecting one storage format over another for LOB data
  3. Move data from LONG and LONG RAW columns to a LOB column
  4. Use LOB commands to adjust the storage size of LOBs
  5. Describe how Oracle uses LOBs to store large varrays
  6. Understand how and why to use temporary LOBs
  7. Discern when to buffer LOBs

Although you may rarely have to use LOB data types for storage in your Oracle database, knowing how to shape the way Oracle uses LOBs can have a significant effect on the overall operation of your database.

Large objects

Interest in the use of large objects (LOBs) is growing, particularly for the storage of nontraditional datatypes such as images. The Oracle database has been able to store large objects for some time. Oracle8 added the capability to store multiple LOB columns in each table. Oracle Database 10g essentially removed the space limitation on large objects. Oracle Database 11g greatly improved the performance of query and insert operations used with LOBs through the introduction of SecureFiles. Transparent data encryption is supported for SecureFiles LOB data.
Out-of-line data is also used to store large objects (LOBs) that are stored internally (as opposed to BFILEs, which are pointers to LOBs external to the database). The combination of object types, object views, collectors, and LOBs provides a strong foundation for the implementation of an object-relational database application. In the next lesson, we will review LOB data types.

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