less_02_performance-tuining_oracle1g

2Copyright © 2008, Oracle. All rights reserved.

Basic Tuning Tools

Copyright © 2008, Oracle. All rights reserved.2 - 2

Objectives

After completing this lesson, you should be able to do the following:• View the top wait events to determine the highest wait• View the time model to diagnose performance issues• Use dynamic performance views to view statistics and wait

events• Use Enterprise Manager Monitoring• Identify the key tuning components of the alert logs• Identify the key tuning components of user trace files


Performance Tuning Diagnostics

Diagnostic tools gather and format the following types of performance data:• Cumulative statistics:

– Wait events with time information– Time model

• Metrics: Statistic rates • Sampled statistics: Active Session History

– Statistics by session– Statistics by SQL– Statistics by service– Other dimensions


Performance Tuning Tools

Available tools:• Basic:

– Time model– Top wait events– Dynamic performance views and tables– Alert log– Trace files– Enterprise Manager pages

• Add-in: Statspack• Options:

– Diagnostics pack– Tuning pack


Tuning Objectives

The objectives of tuning are:• Minimizing response time• Increasing throughput• Increasing load capabilities• Decreasing recovery time


Top Wait Events


DB Time

DB Time =

DB Wait Time +

DB CPU Time


CPU and Wait Time Tuning Dimensions

Scalableapplication

Possiblyneeds SQL

tuning

Needsinstance/RAC

tuning

CPUtime

Waittime

No gain achievedby adding

CPUs/nodes

DB time = DB CPU time + DB wait time


Time Model: Overview

• The time model is a set of statistics that give an overview of where time is spent inside the Oracle database.

• All statistics use the same dimension: time.• The statistics are accessible through:

– V$SYS_TIME_MODEL– V$SESS_TIME_MODEL

• DB time represents the totaltime spent in database calls.

• A tuning goal is to reduce DB time.• Using DB time, you can gauge the performance impact of

any entity of the database.

SQL

PLSQL Con

nectParse

Java

DB time


Time Model Statistics Hierarchy

Failed parse (out of shared memory) elapsed time

DB timeDB CPUConnection management call elapsed time Sequence load elapsed time SQL execute elapsed time

Parse time elapsed Hard parse elapsed time

Hard parse (sharing criteria) elapsed time Hard parse (bind mismatch) elapsed time

Failed parse elapsed time

PL/SQL execution elapsed time Inbound PL/SQL RPC elapsed time PL/SQL compilation elapsed time Java execution elapsed time

Repeated bind elapsed time

Background elapsed time Background CPU time

RMAN CPU time (backup/restore)


Time Model Example


Dynamic Performance Views

Dynamic performance views provide access to information about changing states and conditions in the instance.

Session dataWait events

Memory allocationsRunning SQL

UNDO usageOpen cursors

Redo log usageAnd so on

Oracle instance


Dynamic Performance Views:Usage Examples

SQL> SELECT sql_text, executions 2 FROM v$sqlstats 3 WHERE cpu_time > 200000;

SQL> SELECT * FROM v$session 2 WHERE machine = 'EDRSR9P1' and 3 logon_time > SYSDATE - 1;

SQL> SELECT sid, ctime 2 FROM v$lock WHERE block > 0;

a

b

c


Dynamic Performance Views: Considerations

• These views are owned by SYS.• Different views are available at different times:

– The instance has been started.– The database is mounted.– The database is open.

• You can query V$FIXED_TABLE to see all the view names.• These views are often referred to as “v-dollar views.”• Read consistency is not guaranteed on these views because

the data is dynamic.


Statistic Levels

STATISTICS_LEVEL

BASIC TYPICAL ALL

Recommendeddefault value

Additional statisticsfor manual

SQL diagnostics

Disable all self-tuningcapabilities

V$STATISTICS_LEVEL


Statistics and Wait Events

StatisticsWait events

Reports

Dynamic performance

views


System Statistic Classes

Cache

Debug

RAC

SQLRedo

User

Enqueue

OS

V$SYSSTAT

V$SESSTATV$STATNAME

Systemstatisticclasses


Displaying Statistics

Statistics are collected for:• Sessions

– All sessions V$SESSTAT– Current session V$MYSTAT

• Services V$SERVICE_STATS• System V$SYSSTAT


Displaying SGA Statistics

NAME BYTES RES-------------------------------- ---------- ---Fixed SGA Size 1303132 NoRedo Buffers 17780736 NoBuffer Cache Size 50331648 YesShared Pool Size 142606336 YesLarge Pool Size 4194304 YesJava Pool Size 12582912 YesStreams Pool Size 0 YesShared IO Pool Size 0 YesGranule Size 4194304 NoMaximum SGA Size 836976640 NoStartup overhead in Shared Pool 41943040 NoFree SGA Memory Available 608174080

SQL> SELECT * FROM V$SGAINFO;


Wait Events

• A collection of wait events provides information about the sessions that had to wait or must wait for different reasons.

• These events are listed in the V$EVENT_NAME view, which has the following columns:

– EVENT#– NAME– PARAMETER1– PARAMETER2– PARAMETER3

Wait


Using the V$EVENT_NAME View

NAME PARAMETER1 PARAMETER2 PARAMETER3

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

PL/SQL lock timer duration

alter system set mts_dispatcher waited

buffer busy waits file# block# id

library cache pin handle addr pin address 0*mode+name

log buffer space

log file switch (checkpoint incomplete)

transaction undo seg# wrap# count

...

961 rows selected.

SQL> SELECT name, parameter1, parameter2, parameter3 2 FROM v$event_name;


Wait Classes

Scheduler

Cluster Configuration

Commit

Application

Administrative

Network User I/O

Concurrency

System I/O

Other

Idle

Backgroundprocesses I/O

Foregroundprocesses I/O

DBAcommands

Should berare

Inadequate database/instance configuration

Resource manager

RACresources

Userapplication

code

Inactivesessions

Networkmessaging

log file sync

Internal database resources

V$SESSION_WAIT_CLASS

V$SERVICE_WAIT_CLASS

V$SYSTEM_WAIT_CLASS

V$EVENT_NAME

Waitclasses


Displaying Wait Event Statistics

• Wait event statistics levels:– System– Service– Session

• Wait event statistics columns vary by view.

V$SERVICE_EVENT

V$SYSTEM_EVENT

V$SESSION_EVENT

EVENT X X X

TOTAL_WAITS X X X

TOTAL TIMEOUTS X X X

TIME_WAITED X X X

AVERAGE_WAIT X X X

TIME_WAITED_MICRO X X X

EVENT_ID X X X

TOTAL_WAIT_FG X

TOTAL_TIMEOUTS_FG X

TIME_WAITED_FG X

AVERAGE_WAIT_FG X

TIME_WAITED_MICRO_FG X

SID X

SERVICE_NAME X

SERVICE_NAME_HASH X

WAIT_CLASS_ID X X

WAIT_CLASS# X X

WAIT_CLASS X X


Commonly Observed Wait Events

Wait Event AreaBuffer busy waits Buffer cache, DBWR

Free buffer waits Buffer cache, DBWR, I/O

Db file scattered read, Db file sequential read

I/O, SQL Tuning

Enqueue waits (enq:) Locks

Library cache waits Latches

Log buffer space Log buffer I/O

Log file sync Over-commit, I/O


Using the V$SESSION_WAIT View

SID SEQ# EVENT WAIT STATETIME

--- - -- ---- -------------------------------- -------1 1284 pmon timer 0 WAITING2 1697 rdbms ipc message 0 WAITING3 183 rdbms ipc message 0 WAITING4 4688 rdbms ipc message 0 WAITING5 114 smon timer 0 WAITING6 14 SQL*Net message from client -1 WAITED

SHORTTIME

SQL> SELECT sid, seq#, event, wait_time, state 2 FROM v$session_wait;


Precision of System Statistics

• Views that include microsecond timings:– V$SESSION_WAIT, V$SYSTEM_EVENT,

V$SERVICE_EVENT, V$SESSION_EVENT (TIME_WAITED_MICRO column)

– V$SQL, V$SQLAREA (CPU_TIME, ELAPSED_TIME columns)

– V$LATCH, V$LATCH_PARENT, V$LATCH_CHILDREN (WAIT_TIME column)

– V$SQL_WORKAREA, V$SQL_WORKAREA_ACTIVE (ACTIVE_TIME column)

• Views that include millisecond timings:– V$ENQUEUE_STAT (CUM_WAIT_TIME column)


Using Features of the Packs

• SQL traces• Statspack• System statistics• Wait model• Time model• OS statistics• Metrics• Service statistics• Histograms• Optimizer statistics• SQL statistics

Monitoring and tuningwith packs

Monitoring and tuning without packs

Database Configuration Management Pack• Database and Host Configuration• Deployments • Patch Database and View Patch Cache • Patch staging • Clone Database • Clone Oracle Home • Search configuration • Compare configuration • Policies

Database Diagnostics Pack• Automatic Workload Repository• Automatic Database Diagnostic Monitor (ADDM)• Active Session History (ASH)• Performance monitoring (database and host)• Event notifications: notification methods, rules, and schedules• Event history and metric history (database and host)• Blackouts• Dynamic metric baselines• Monitoring templates

Database Tuning Pack• SQL Access Advisor• SQL Tuning Advisor• Automatic SQL Tuning• SQL Tuning Sets• Automatic Plan Evolution of SQL Plan Management• SQL Monitoring• Reorganize objects


Accessing the Database Home Page

https://host name:1158/em


Enterprise Manager Performance Pages


Viewing the Alert Log

Database Home page > Related Links region >Alert Log Contents


Using Alert Log Information as an Aid in Tuning

The alert log file contains the following information that can be used to aid in tuning the database:• Time to perform archiving• Instance recovery start and complete times• Deadlock and timeout errors• Incomplete checkpoints• Checkpoint start and end times


User Trace Files

• Server-process tracing can be enabled or disabled at the session or instance level.

• A user trace file contains statistics for traced SQL statements in that session.

• User trace files are created on a per server process basis.• User trace files can also be created by:

– Performing a BACKUP CONTROL FILE TO TRACE– Process errors


Background Processes Trace Files

• The Oracle database server dumps information about errors detected by any background process into trace files.

• Oracle Support uses these trace files to diagnoseand troubleshoot.

• These files do not usually contain tuning information.


Summary

In this lesson, you should have learned how to:• View the top wait events to determine highest wait• View the time model to diagnose performance issues• Use dynamic performance views to view statistics and wait

events• Use Enterprise Manager Monitoring• Identify the key tuning components of the alert logs• Identify the key tuning components of user trace files


Practice 2 Overview:Using Basic Tools

This practice covers the following topics:• View the top waits events and the time model• Use the alert log information for tuning• View system statistics• View wait events

less_02_performance-tuining_oracle1g

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