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Managing Database Storage Structures

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Objectives

After completing this lesson, you should be able to do the following:

• Describe how table row data is stored in blocks

• Define the purpose of tablespaces and data files

• Create and manage tablespaces

• Obtain tablespace information

• Describe the main concepts and functionality of Automatic Storage Management (ASM)

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Storage Structures

Database

Tablespace

Segment

Extent

Oracle datablock

Logical Physical

OSblock

OS file

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How Table Data Is Stored

Tablespace

Table A Table B

SegmentSegment

Rows

Columns

Table

Blocks

Row piece Extent

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Anatomy of a Database Block

Block header

Free space

Row data

Growth

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Tablespaces and Data Files

The Oracle database stores data logically in tablespaces and physically in data files.

• Tablespaces:– Can belong to only one database– Consist of one or more data files– Are further divided into logical units of storage

• Data files:– Can belong to only one

tablespace and one database– Are a repository for schema

object data

Database

Tablespace

Data files

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Space Management in Tablespaces

• Locally managed tablespace:– Free extents are managed in the tablespace.– A bitmap is used to record free extents.– Each bit corresponds to a block or group of blocks.– The bit value indicates free or used extents.– The use of locally managed tablespaces is

recommended.

• Dictionary-managed tablespace:– Free extents are managed by the data dictionary.– Appropriate tables are updated when extents are

allocated or unallocated.– These tablespaces are supported only for backward

compatibility.

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Creating a New Tablespace

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Storage for Locally Managed Tablespaces

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Tablespaces in the Preconfigured Database

• SYSTEM• SYSAUX• TEMP

• UNDOTBS1• USERS• EXAMPLE

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Altering a Tablespace

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Actions with Tablespaces

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Dropping Tablespaces

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Viewing Tablespace Information

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Where We Are

• Using tablespaces to separate data• Creating various types of tablespaces• Managing tablespaces• Obtaining tablespace information

• Describe the main concepts and functionality of Automatic Storage Management (ASM)

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What Is Automatic Storage Management?

• Is a portable and high-performancecluster file system

• Manages Oracle database files

• Spreads data across disksto balance load

• Mirrors data

• Solves many storage management challenges

ASM

Filesystem

Volumemanager

Application

Database

Operating system

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ASM: Key Features and Benefits

• Stripes files, but not logical volumes

• Provides online disk reconfiguration and dynamic rebalancing

• Allows for adjustable rebalancing speed

• Provides redundancy on a per-file basis

• Supports only Oracle database files

• Is cluster aware

• Is automatically installed

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ASM: Concepts

Database

Tablespace

Segment

Extent

Oracle datablock

Data file

Physicalblock

ASM disk

ASM file

Allocation unitFile system

fileor

Raw device

ASMdisk group

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Summary

In this lesson, you should have learned how to:

• Describe how table row data is stored in blocks

• Define the purpose of tablespaces and data files

• Create and manage tablespaces

• Obtain tablespace information

• Describe the main concepts and functionality of ASM, such as:– Disk mirroring– Dynamic rebalancing– ASM disk groups

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Practice Overview:Managing Database Storage Structures

This practice covers the following topics:

• Creating tablespaces

• Gathering information about tablespaces