Oracle Basic Storage Concepts and Settings

transcript

OracleBasic 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

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 15MDEFAULT 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

Configuring and Viewing StorageSyntax:

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

Configuring and Viewing Storage

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;

Querying the Data Dictionary For Storage Data

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

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

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

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

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

Oracle Basic Storage Concepts and Settings

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