Chapter 6 Basic Storage Concepts and Settings

Oracle9i Database Administrator: Implementation and Administration 1

Chapter 6

Basic Storage Concepts

and Settings


Objectives

Differentiate between logical and physical structures

Create many types of tablespaces Configure and view storage for

tablespaces and datafiles Use undo data


Introduction to Storage Structures

Internal structures store:

The structure of every table, view, and other objects you create

The data you load into your tables and other objects

Information about the structure of tables, views, etc. (metadata)



Physical structures:•Datafiles•Operating system blocks•Redo log files•Control files



Logical Structures:•Data block•Extent•Segment•Schema object•Tablespace



Logical data blocks map directly to contiguous operating system blocks in datafiles


Tablespaces and Datafiles

CREATE TABLESPACE <tablespacename> DATAFILE <filename> SIZE <nn> AUTOEXTEND ON|OFF TEMPORARY|PERMANENTEXTENT MANAGEMENT LOCAL|DICTIONARYLOGGING|NOLOGGINGONLINE|OFFLINESEGMENT SPACE MANAGEMENT MANUAL|AUTO

Add multiple files, separated by commas if neededClause is required for user managed filesClause is optional when using OMFCan be used to specify SIZE of OMF file

Note: additional sub-clauses shown later




TEMPORARY: This option used only when creating temporary tablespaces that are dictionary-managed. PERMANENT: Default option; stores permanent objects such as tables and indexes




LOCAL: Default; tablespace manages extent free space in a bitmap inside the tablespaceDICTIONARY: tablespace manages extent free space in the data dictionary

Note: additional sub-clauses shown later




LOGGING: Default; all DML, DDL, and mass INSERT commands recorded in redo logNOLOGGING: only DML commands recorded in redo log




ONLINE: Default; available for useOFFLINE: not available for use




AUTO: Manages segment free space in a bitmap in the tablespaceMANUAL: Manages segment free space in the data dictionary


Implementing OMF With Tablespaces

DB_CREATE_FILE_DEST must be set: In init<sid>.ora

Or, during session

CREATE TABLESPACE command: Omit DATAFILE clause in

Or, include DATAFILE clause but only include SIZE clause (omit file name)


The DATAFILE Clause

DATAFILE '<datafilename>'

SIZE <nn>|REUSE

AUTOEXTEND ON|OFF

MAXSIZE <nn>|UNLIMITED

SIZE <nn>: Specify size in bytes, kilobytes, or megabytes REUSE: File already exists

AUTOEXTEND ON: Allow file to expand when Oracle determines more space is needed AUTOEXTEND OFF: Do not expand file


The DATAFILE Clause

DATAFILE '<datafilename>'

SIZE <nn>|REUSE

AUTOEXTEND ON|OFF

MAXSIZE <nn>|UNLIMITED

Used with AUTOEXTEND ON:MAXSIZE <nn>: Specify maximum file size in bytes, kilobytes, or megabytes UNLIMITED: File can grow to limits of operating system


The EXTENT MANAGEMENT and SEGMENT SPACE MANAGEMENT Clauses

Syntax for: EXTENT MANAGEMENT LOCAL:

EXTENT MANAGEMENT LOCAL|DICTIONARY

AUTOALLOCATE|UNIFORM SIZE <nn>

SEGMENT SPACE MANAGEMENT MANUAL|AUTO

MINIMUM EXTENT <nn>

DEFAULT STORAGE (INITIAL <nn> NEXT <nn> PCTINCREASE <nn>

MINEXTENTS <nn> MAXEXTENTS <nn>)

AUTO: Manages segment free space in a bitmap in the tablespaceMANUAL: Manages segment free space in the data dictionary

AUTOALLOCATE: Allow the system to manage extent size for all tables and other objects created in the tablespaceUNIFORM SIZE <nn>: Require the specified extent size for all tables and other objects created in the tablespace


The EXTENT MANAGEMENT and

SEGMENT SPACE MANAGEMENT Clauses

Syntax for dictionary-managed tablespace:

EXTENT MANAGEMENT LOCAL|DICTIONARY

SEGMENT SPACE MANAGEMENT MANUAL|AUTO

AUTOALLOCATE|UNIFORM SIZE <nn>

MINIMUM EXTENT <nn>

DEFAULT STORAGE

(INITIAL <nn> NEXT <nn> PCTINCREASE <nn>


Minimum extent size allowed for any object created in the tablespace

Default storage settings for any object created in the tablespace without a STORAGE clause of its own


The EXTENT MANAGEMENT Clause

Example: A new table needing 6 M of space skips over the deallocated extents

Coalesce free space periodically to combine deallocated extents

Example of dictionary-managed datafile


Creating a Dictionary-Managed Tablespace

Example:

CREATE TABLESPACE USER_TEST

DATAFILE 'D:\oracle\data\user_test01.dbf' SIZE 250M

AUTOEXTEND ON

EXTENT MANAGEMENT DICTIONARY

MINIMUM EXTENT 15M

DEFAULT STORAGE (INITIAL 90M NEXT 15M PCTINCREASE 0

MINEXTENTS 1 MAXEXTENTS 50);


Creating a Locally Managed Tablespace

Example of locally managed datafile

Example: A new table needing a 10M extent would use the free space from two 5 M deallocated extents

Deallocated extents are automatically coalesced

All new tables must use extents of the same size or multiples of the size


Creating a Locally Managed Tablespace

Example:

CREATE TABLESPACE USER_AUTO

DATAFILE '<C:oracle\oradata\user_auto01.dbf'

SIZE 20M AUTOEXTEND OFF

EXTENT MANAGEMENT LOCAL AUTOALLOCATE

SEGMENT SPACE MANAGEMENT AUTO;


Segment Types and Their Uses

Data segment: for tables, object tables, triggers

Index segment: for indexes Temporary segment: for sorting

operations and temporary tables Rollback segment: for undo data LOB segment: for LOB data stored

separately from the rest of the table’s data


Temporary Tablespaces

Oracle recommends creating locally managed temporary tablespaces

Used for temporary segments

Command syntax:CREATE TEMPORARY TABLESPACE <tablespacename>

TEMPFILE <filename> SIZE <nn> AUTOEXTEND ON|OFF

EXTENT MANAGEMENT LOCAL UNIFORM SIZE <nn>


Tablespaces With Nonstandard Data Block Size Can be 2 K, 4 K, 8 K, 16 K, or 32 K

Requires a special memory cache that matches the block size

Create cache by setting the appropriate initialization parameter:

DB_2K_CACHE_SIZE

DB_4K_CACHE_SIZE

DB_8K_CACHE_SIZE

DB_16K_CACHE_SIZE

DB_32K_CACHE_SIZE


Tablespaces With Nonstandard Data Block Size

Example:

CREATE TABLESPACE TBS_2K

DATAFILE '<C:\oracle\oradata\tbs_2k.dbf'

SIZE 4M BLOCKSIZE 2K;


Configuring and Viewing Storage

Changes you can make to a tablespace: LOGGING/NOLOGGING

PERMANENT/TEMPORARY

READ ONLY/READ WRITE

Coalesce contiguous storage space

Add new datafile

Rename a datafile

Change size of a datafile



Syntax:

ALTER TABLESPACE <tablespacename>

ADD|RENAME DATAFILE <filename>

SIZE <nn> AUTOEXTEND ON|OFF REUSE

DEFAULT STORAGE (INITIAL <nn> NEXT <nn>

PCTINCREASE <nn>


MINIMUM EXTENT <nn>

COALESCE



Taking a tablespace offline: Stops it from being accessed by users

Methods for taking a tablespace offline: NORMAL: default

TEMPORARY: for damaged datafiles

IMMEDIATE: for damaged disk (media)


Read-only Tablespaces

Can only be queried

No inserts, updates, or deletes

Example:

ALTER TABLESPACE ACCOUNTING READ ONLY;


Dropping Tablespaces

Syntax:

DROP TABLESPACE <tablespacename>

INCLUDING CONTENTS

AND DATAFILES

CASCADE CONSTRAINTS;

Use when there is data in the tablespace

Use when there are constraints outside the tablespace that reference this tablespace


Querying the Data Dictionary For Storage Data



Example:

Find adjacent free extents that should be coalesced

SELECT BLOCK_ID, BLOCK_ID+BLOCKS NEXT_BLOCK_ID, BLOCKS

FROM DBA_FREE_SPACE

WHERE TABLESPACE_NAME = 'USERS'

ORDER BY BLOCK_ID;



Identifying adjacent free sets of blocks


Overview of Undo Data

Undo data is made of undo blocks

Contain before images of data blocks

Assist in read-consistency

Two methods for managing: Manual: the old way (with manually created redo

segments)

Automatic: the new way (with undo tablespace)


Implementing Automatic Undo Management

Requirements: Set initialization parameters:

UNDO_MANAGEMENT=AUTO

UNDO_TABLESPACE=<tablespacename>

Create UNDO tablespace: While creating the database

Later with CREATE UNDO TABLESPACE command


Implementing Automatic Undo Management

Optional initialization parameters: UNDO_RETENTION: time in seconds that undo

data is saved after commit (default is 900 seconds)

UNDO_SURPRESS_ERRORS: defines error handling when transitioning from manual to automatic undo management


Chapter Summary Database structures are divided into logical

and physical groups

Physical structures include datafiles, control files, and redo log files

Logical structures include tablespaces, extents, and data blocks

A tablespace always has at least one datafile where its data is stored

Locally managed tablespaces use a bitmap to track extent free space


Chapter Summary When using OMF, omit the DATAFILE clause in

the CREATE TABLESPACE command

AUTOEXTEND ON allows a datafile to grow as needed

Dictionary-managed tablespaces: Use the data dictionary to track extent free space

Don’t automatically coalesce free space

Locally managed tablespaces: Automatically coalesce free space

Keep all extents the same size or a variable system-controlled size


Chapter Summary

Types of segments: data, index, temporary, and rollback

Temporary tablespaces store data while sorting, and temporary tables

Tablespaces can be ONLINE or OFFLINE

A READ ONLY tablespace is not included in regular backups or recoveries


Chapter Summary

Dropping a tablespace with INCLUDING CONTENTS destroys all its data

Data dictionary views for tablespaces include DBA_TABLESPACES and DBA_FREE_EXTENTS

Undo data gives users read consistency

Automatic undo management uses an UNDO tablespace

Documents

Chapter 6 Basic Storage Concepts and Settings