11gR2 Less05 Storage

5Copyright © 2009, Oracle. All rights reserved.

Storage Enhancements

Copyright © 2009, Oracle. All rights reserved.5 - 2

Objectives

After completing this lesson, you should be able to:

• Use 4 KB sector disks

• Employ data compression

• Create a SQL Access Advisor analysis session using Enterprise Manager

• Create a SQL Access Advisor analysis session using PL/SQL

• Use deferred segment creation


Supporting 4 KB Sector Disks

• Emulation mode:LBA0 LBA1 LBA2 LBA3 LBA4 LBA5 LBA6 LBA7

4096-byte physical sector

• Native mode:

LBA0

4096-byte physical sector

Logical sector

Physical sector

11.2


Using 4 KB Sector Disks

Emulation mode:• Recommended 4 KB block

size for redo logs • Recommended 4 KB block

size (or larger) for data files

Native mode:• Mandatory 4 KB block size

for redo logs • Mandatory 4 KB block size

(or larger) for data filesNot affected:• Control file block size: 16 KB

Database

Data filesControl

filesOnline redo

log filesArchived log files

11.2


Specifying the Disk Sector Size

Specify the sector size for disk drives with the new SECTOR_SIZE and BLOCKSIZE clauses of the following commands:

• CREATE DISKGROUP • ALTER DATABASE• CREATE DATABASE• CREATE CONTROL FILE

11.2


Using the SECTOR_SIZE Clause

Create a disk group in ASM with a 4 KB sector size:

CREATE DISKGROUP mydgroup1 NORMAL REDUNDANCY

FAILGROUP mycontroller1 DISK

'/devices/diska1',

'/devices/diska2',

'/devices/diska3',

'/devices/diska4'

FAILGROUP mycontroller2 DISK

'/devices/diskb1',

'/devices/diskb2',

'/devices/diskb3',

'/devices/diskb4'

ATTRIBUTE 'sector_size'='4096';

11.2


Creating a Database with 4 KB Sector Disks

• No extra work• No GUI change• Default sector size based on hardware (not the earlier 512

bytes sectors)

CREATE DATABASE sample NORESETLOGS FORCE LOGGING ARCHIVELOGLOGFILE GROUP 1 '$ORACLE_BASE/oradata/sample/redo01.log'

SIZE 100M BLOCKSIZE 4096, GROUP 2 '$ORACLE_BASE/oradata/sample/redo02.log‘

SIZE 100M BLOCKSIZE 4096DATAFILE...

11.2


Specifying BLOCKSIZE

ALTER DATABASE sample ADD LOGFILE GROUP 3 ('$ORACLE_BASE/oradata/sample/redo03a.log', '$ORACLE_BASE/oradata/sample/redo03b.log')

SIZE 500K BLOCKSIZE 4096;

CREATE CONTROLFILE REUSE DATABASE sample NORESETLOGS FORCE LOGGING ARCHIVELOG

…

LOGFILE

GROUP 1 '$ORACLE_BASE/oradata/sample/redo01.log'

SIZE 100M BLOCKSIZE 4096, GROUP 2 '$ORACLE_BASE/oradata/sample/redo02.log '

SIZE 100M BLOCKSIZE 4096DATAFILE

…

11.2


Determining Your Log File Block Size

• Viewing the V$LOG or V$STANDBY_LOG views in the data dictionary

• New BLOCKSIZE column

SQL> desc v$log

Name Null? Type

--------------------------------- -------- ------------

GROUP# NUMBER

THREAD# NUMBER

SEQUENCE# NUMBER

BYTES NUMBER

BLOCKSIZE NUMBER

MEMBERS NUMBER

ARCHIVED VARCHAR2(3)

STATUS VARCHAR2(16)

FIRST_CHANGE# NUMBER

FIRST_TIME DATE

11.2


Performing an Offline Migration to 4 KB Disks

• Premigration (4 KB disks, back up and shut down Oracle Database 11g Release 2)

• Migration:1. Move backup files to 4 KB disks.

2. Mount database.

3. Add log file groups on 4 KB disks.

4. Confirm their status.

5. Open the database.

6. Switch logs to 4 KB log group.

• Postmigration (Query log file status and drop old log files)

11.2


Quiz

You must use 4 KB log files on 4 KB native mode disks.

1. True

2. False


Table Compression: Overview

• Oracle Database 11g extends compression for OLTP data.– Support for conventional DML operations

(INSERT, UPDATE, DELETE)

• New algorithm significantly reduces write overhead.– Batched compression ensures no impact for most OLTP

transactions.

• No impact on reads– Reads may actually see improved performance due to

fewer I/Os and enhanced memory efficiency.


Table Compression Concepts

Header

Un

com

pre

ssed

dat

aCompressed

data

Freespace Inserts are

uncompressed.

PCTFREE reachedtriggers compression.

Inserts are againuncompressed.

PCTFREE reachedtriggers compression.

Data block

PCTFREElimit


Compressing Table Data

Compression Method

Compression Ratio

CPU Overhead

CREATE and ALTER TABLE Syntax

Typical Apps

Basic compression

High Minimal COMPRESS [BASIC] DSS

OLTP table compression

High Minimal COMPRESS FOR OLTP

OLTP, DSS

11.2 update


Using OLTP Compression

• Requires database compatibility level at 11.1 or greater

• New syntax extends the COMPRESS keyword:– COMPRESS [BASIC | FOR OLTP]– BASIC is the default: Refers to bulk-load operations from

prior releases– FOR OLTP: OLTP + direct loads

• Enable compression for new tables:

• Enable compression on an existing table:

– Does not trigger compression on existing rows

CREATE TABLE t1 COMPRESS FOR OLTP;

ALTER TABLE t2 COMPRESS FOR OLTP;

11.2 changes


Using the Compression Advisor

• A compression advisor helps to determine optimal compression ratios.

• The DBMS_COMPRESSION package includes the GET_COMPRESSION_RATIO procedure.

11.2

BEGINDBMS_COMPRESSION.GET_COMPRESSION_RATIO ('USERS','SH','SALES', NULL,DBMS_COMPRESSION.COMP_FOR_OLTP, blkcnt_cmp, blkcnt_uncmp, rowcnt_cmp, rowcnt_uncmp, comptype);DBMS_OUTPUT.PUT_LINE('Blk count compressed = ' || blkcnt_cmp);DBMS_OUTPUT.PUT_LINE('Blk count uncompressed = ' || blkcnt_uncmp);DBMS_OUTPUT.PUT_LINE('Row count per block compressed = ' || rowcnt_cmp);DBMS_OUTPUT.PUT_LINE('Row count per block uncompressed = ' || rowcnt_uncmp);DBMS_OUTPUT.PUT_LINE('Compression type = ' || comptype);DBMS_OUTPUT.PUT_LINE('Compression ratio = '||blkcnt_uncmp/blkcnt_cmp||' to 1');


Viewing Table Compression Information

*_TABLES views have new columns:

• COMPRESSION: Indicates whether table compression is enabled (ENABLED) or not (DISABLED)

• COMPRESS_FOR: Type of compression


SQL Access Advisor: Overview

Workload

SQL Access Advisor

Solution

Component of CBO

Provides implementation

script

No expertiserequired

DBA

Whatpartitions, indexes, and MVs do I need

to optimizemy entire

workload?


SQL Access Advisor: Usage Model

Indexes Materializedviews

Materializedviews log

SQL Access Advisor

Hypothetical

SQL cache

Filter Options

STS

Workload

Partitionedobjects


Possible Recommendations

Recommendation Comprehensive Limited

Add new (partitioned) index on table or materialized view. YES YES

Drop an unused index. YES NO

Modify an existing index by changing the index type. YES NO

Modify an existing index by adding columns at the end. YES YES

Add a new (partitioned) materialized view. YES YES

Drop an unused materialized view (log). YES NO

Add a new materialized view log. YES YES

Modify an existing materialized view log to add new columns or clauses.

YES YES

Partition an existing unpartitioned table or index. YES YES


Using SQL Access Advisor


SQL Access Advisor: PL/SQL Procedure Flow

SQLAccess Advisor

task

CREATE_TASKUPDATE_TASK_ATTRIBUTESDELETE_TASKQUICK_TUNE

SET_TASK_PARAMETERRESET_TASK

ADD_STS_REFDELETE_STS_REFEXECUTE_TASKINTERRUPT/CANCEL_TASKMARK_RECOMMENDATIONUPDATE_REC_ATTRIBUTES GET_TASK_REPORTGET_TASK_SCRIPT

Step 1

Step 2

Step 3

Report/Scripts

Task-dependent

Advisor-dependent


SQL Access Advisor: PL/SQL Example

BEGIN dbms_advisor.create_task(dbms_advisor.sqlaccess_advisor,'MYTASK'); END;

BEGIN

dbms_advisor.add_sts_ref('MYTASK','SH','MYSTS'); dbms_advisor.execute_task('MYTASK');

dbms_output.put_line(dbms_advisor.get_task_script('MYTASK')); END;

1

3

BEGINdbms_advisor.set_task_parameter('MYTASK','ANALYSIS_SCOPE','ALL'); dbms_advisor.set_task_parameter('MYTASK','MODE','COMPREHENSIVE'); END;

2


Temporary Tablespace Shrink

• Sort segment extents are managed in memory after being physically allocated.

• This method can be an issue after big sorts are done.• To release physical space from your disks, you can

shrink temporary tablespaces: – Locally managed temporary tablespaces– Online operation

CREATE TEMPORARY TABLESPACE temp TEMPFILE 'tbs_temp.dbf' SIZE 600m REUSE AUTOEXTEND ON MAXSIZE UNLIMITEDEXTENT MANAGEMENT LOCAL UNIFORM SIZE 1m;

ALTER TABLESPACE temp SHRINK SPACE [KEEP 200m];

ALTER TABLESPACE temp SHRINK TEMPFILE 'tbs_temp.dbf';


DBA_TEMP_FREE_SPACE

• Lists temporary space usage information

• Central point for temporary tablespace space usage

Column name Description

TABLESPACE_NAME Name of the tablespace

TABLESPACE_SIZE Total size of the tablespace, in bytes

ALLOCATED_SPACE Total allocated space, in bytes, including space that is currently allocated and used and space that is currently allocated and available for reuse

FREE_SPACE Total free space available, in bytes, including space that is currently allocated and available for reuse and space that is currently unallocated


Tablespace Option for Creating Temporary Table

• Specify which temporary tablespace to use for your global temporary tables.

• Decide a proper temporary extent size.

CREATE TEMPORARY TABLESPACE temp TEMPFILE 'tbs_temp.dbf' SIZE 600m REUSE AUTOEXTEND ON MAXSIZE UNLIMITEDEXTENT MANAGEMENT LOCAL UNIFORM SIZE 1m;

CREATE GLOBAL TEMPORARY TABLE temp_table (c varchar2(10)) ON COMMIT DELETE ROWS TABLESPACE temp;


Segment Creation on Demand

• Segment creation is deferred until the first row is inserted.

• DEFERRED_SEGMENT_CREATION = TRUE (default)

CREATE TABLE INSERT INTO

• Save disk space

• Improve installation time

of applications with

large schemas

11.2


Creating Tables Without Segments

SQL> SHOW PARAMETERS deferred_segment_creation

NAME TYPE VALUE

------------------------------------ ----------- ------

deferred_segment_creation boolean TRUE

SQL> CREATE TABLE seg_test(c number, d varchar2(500));Table created.SQL> SELECT segment_name FROM user_segments; no rows selected

SQL> INSERT INTO seg_test VALUES(1, 'aaaaaaa');1 row created.

SQL> SELECT segment_name FROM user_segments;

SEGMENT_NAME

-------------------------------------------------------

SEG_TEST

Inserting rows and creating segments:

11.2


Controlling Deferred Segment Creation

With DEFERRED_SEGMENT_CREATION parameter in the:

• Initialization parameter file

• ALTER SESSION command

• ALTER SYSTEM command

With SEGMENT CREATION clause:

• IMMEDIATE• DEFERRED (default in Oracle Database 11g Release 2)

CREATE TABLE seg_tab3(c1 NUMBER, c2 NUMBER)

SEGMENT CREATION IMMEDIATE TABLESPACE seg_tbs;

CREATE TABLE seg_tab4(c1 NUMBER, c2 NUMBER)

SEGMENT CREATION DEFERRED;

Note: Indexes inherit table characteristics.

11.2


Restrictions and Exceptions

Segment creation on demand:

• Only for nonpartitioned heap tables and nonpartitioned indexes

• Not for IOTs, clustered tables, or other special tables

• Not for tables in dictionary-managed tablespaces

Note: If you were to migrate a table without segments from a locally managed to a dictionary-managed tablespace, you must drop and re-create it.

11.2


Additional Automatic Functionality

• No segments for unusable indexes and index partitions

• Creating an index without a segmentCREATE INDEX test_i1 ON seg_test(c) UNUSABLE;

• Removing any allocated space for an indexALTER INDEX test_i UNUSABLE;

• Creating the segment for an index: ALTER INDEX test_i REBUILD;

11.2


Quiz

Which of the following statements are true for Oracle Database 11g Release 2?

1. Deferred segment creation is always enabled. You cannot control it.

2. You can control the deferred segment creation with the SEGMENT CREATION clause of the CREATE TABLE command.

3. Segment creation on demand is available for all types of tables, including those owned by the SYS user.

4. Segment creation on demand is available for nonpartitioned tables.


Summary

In this lesson, you should have learned how to:

• Use 4 KB sector disks

• Employ data compression

• Create a SQL Access Advisor analysis session using Enterprise Manager

• Create a SQL Access Advisor analysis session using PL/SQL

• Use deferred segment creation


Practice 5: Overview

This practice covers using table compression.

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11gR2 Less05 Storage