26928-00 reva oracle tuning for sa&apps

8/8/2019 26928-00 RevA Oracle Tuning for SA&Apps

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Tuning Oracle with Consideration forStorage and Your Application Mix

James F. Koopmann

Technical White Paper26928-00, Rev. AFebruary 2007


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Copyright 2007 LSI Logic Corporation. All rights reserved.


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Tuning Oracle: Your Application Mix iii

Contents

Chapter 1: I NTRODUCTION

Chapter 2: U NDERSTANDING THE APPLICATION M IX

Determining Oracle Workloads................................................................................................2-2

Workload for Existing Oracle Database...................................................................................2-3

Chapter 3: A NALYZING SQL

Oracle Trace ........................ ......................... ........................ ........................ ............................ 3-1

Creating a Trace ...................... ........................ .......................... ......................... ...................... 3-2

Original Method..................................................................................................................3-2Newer Method Using DBMS_MONITOR Package...........................................................3-2

Generated Trace Files .......................... ........................... .......................... ......................... .3-3

Active Sessions ......................... ......................... ........................ ........................... ................... 3-4

V$SESSION........................................................................................................................3-4

V$SQLAREA .................... ........................ .......................... ......................... ...................... 3-5

DBMS_XPLAN Procedure.................................................................................................3-7

V$SQL_PLAN_STATISTICS............................................................................................3-7

V$SQLTEXT...................... .......................... .......................... ......................... ................... 3-8V$SESS_IO ........................ .......................... ........................ .......................... .................... 3-9

Chapter 4: R ESOURCE C ONTENTION

True Session Wait Activity in Oracle 10g ...................... ........................ ......................... ........4-1

Resource Currently in High Demand..................................................................................4-2

What User is Waiting the Most .....................................................................................4-2

SQL Currently Using the Most Resources..........................................................................4-3

What Object is Currently Causing the Highest Resource Waits.........................................4-3


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iv Tuning Oracle: Your Application Mix

Chapter 5: C ONCLUSION

Contact Information ....................... ........................ .......................... ......................... ...............5-1

North American Headquarters ......................................................................................5-1

LSI Logic KK Headquarters .........................................................................................5-1

LSI Logic Europe Ltd. European Headquarters ......................... ............................ ......5-1

References ...................... .......................... .......................... ........................ ........................... ...5-2


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Tuning Oracle: Your Application Mix 1-1

Chapter 1

Introduction

As a database administrator you already know that tuning an Oracle database is a complextask. With hundreds of features and numerous application interfaces, you must weightuning decisions carefully, and not lose sight of the intricacy of the full system. In facttuning Oracle is not a one-person job. Oracle tuning requires not only the databaseadministration staff but others who understand the full intent of the database and theapplications:

Developers System administrators

Storage administrators

Architects

Business personnel

You can address the complex task of tuning an Oracle database using a systematicapproach. This paper looks at the application aspects of tuning an Oracle database. Otherpapers address the aspects of database files and memory.

An application is made up of code, procedural logic and SQL, that accesses the underlyingOracle database objects and causes input/output (I/O) on the storage array. The applicationand its connected sessions request information. These requests initiate requests forphysical I/O with the storage array. While this information is basic, it is sometimesforgotten in the high speed at which development staffs are required to work and producesolutions.

The performance you get out from the storage array is directly linked through the databaseand ultimately to applications that request the information on disk drives.

A poorly configured database system makes any application perform poorly.

A poorly written application inhibits a database system from performing optimally.

No tuning effort is valid without considering whether the application is requestinginformation optimally.


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Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1-2 Tuning Oracle: Your Application Mix

Specifically, this paper focuses on these factors:

Understanding the application mix

Determining Oracle workload

Identifying methods for analyzing the Oracle sessions: Oracle trace

Active sessions

Resource contention

After you have analyzed your storage system, you can make the following decisions forimproved performance:

Reconfiguring to allow for better IOPS or MBps

Moving data files around to use more disk drives

Adding more disk drives for higher throughput

Purchasing additional storage equipment

Reducing IOPS or MBps through the application


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Chapter 2

Understanding the Application Mix

Understanding the application mix that accesses an Oracle database is vital inunderstanding the workload mix placed on a database and ultimately the performancerequirements of the storage system. With an understanding of the application mix, you canmake many of the adjustments to the configuration parameters within Oracle or thestorage array.

Applications can be categorized as either online transaction processing (OLTP) or online

analytical processing (OLAP): Typically, OLTP applications have these characteristics:

Read and write intensive

Transaction-based with performance based on I/Os per second (IOPS) along withaverage latency or I/O turn-around time

Large bursts of small reads followed by inserts and updates

Mostly driven by the database issuing small random I/Os the size of the definedOracle database block size (db_block_size)

Database block size ranging from 2KB to 32KB with 8KB being average

IMPORTANT Be aware that although a database may have a low write percentage,the database logs might make up for this with writes and must beconsidered. Certain operations such as table scans or index scans,backups, and parallel queries also can issue large I/Os.

Identify the reads-to-writes percentage as this is a critical ratio for determining storageconfigurations. A typical ratio is 70:30.

Typically OLAP applications have these characteristics: Considered as data warehouses or reporting systems Categorized as throughput-based and performance is based on moving large

amounts of data in mega-bytes per second (MBps)

Almost always purely read-only databases except during the load stage

Primarily large multi-block read and write I/O streams


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Understanding the Application Mix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .


Keep in mind that application mixes might change:

A simple OLTP database could be cloned to a different system and begin to be usedwith an OLAP application. The data is the same, but the I/O pattern is very different.

A new group of power users that could turn an OLTP into an OLAP reporting enginewithout giving notice.

The application mix might change throughout the day.

Database backups that run during the day will change the type of read activity of thedatabase.

Data loads or extraction, transformation, and load (ETL) processing could switch anOLAP environment into an OLTP environment.

Determining Oracle WorkloadsAn Oracle workload is often representative of its application mix. Understanding andtranslating an application mix into a database workload is critical for optimizing a storagesystem. By determining the workload, you can better set the various parameters. Keep inmind that a single storage system if configured for two different workload types will notperform as well as a single storage system configured for a single workload type. Just asthere are basically two application mixes there are two primary workload types, smallrandom I/O and large sequential I/O.

Small random I/O

OLTP applications

Transaction-based (IOPS & latency) High levels of IOPS requiring more back-end drives

Large sequential I/O

OLAP applications

Throughput-based (MBps)

High levels of MBps that can often be satisfied by less back-end drives

Large random I/O is a less common workload that you might need to consider. Because of various database traffic or configurations, large sequential I/O may be turned into largerandom I/O at the disk drive level of the storage system. Here are some examples:

Large sequential I/O caused by data warehouses, reporting applications, or utilitiessuch as backups that typically request large I/O streams can be broken up bynormal small random I/O of an OLTP system.

Striping will spread large sequential I/O across many disk drives that cause thestorage array to experience large random I/O.


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. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Workload for Existing Oracle Database


Database systems often are predominantly one of the three previously mentionedworkloads. However, there are times when a database exhibits one or more of thoseworkloads continually and thus falls into the category of a mixed I/O workload.

Workload for Existing Oracle DatabaseIf an existing Oracle 10g Release 2 (10gR2) database is available, use this SQL statementto determine the workload.

set linesize 100set head off

SELECT 'Number of Small Reads :'||sum(decode(name,'physical read total IO

requests',value,0)-decode(name,'physical read total multi block

requests',value,0)),'Number of Small Writes:'||sum(decode(name,'physical write total IO

requests',value,0)-decode(name,'physical write total multi block

requests',value,0)),'Number of Large Reads :'||sum(decode(name,'physical read total multi block

requests',value,0)),'Number of Large Writes:'||sum(decode(name,'physical write total multi block

requests',value,0)),'Total Bytes Read :'||

sum(decode(name,'physical read total bytes',value,0)),'Total Bytes Written :'||sum(decode(name,'physical write total bytes',value,0))

FROM gv$sysstat;

Here is an example of the statistics that might be returned:

Number of Small Reads :205903Number of Small Writes:106883Number of Large Reads :40298Number of Large Writes:2791Total Bytes Read :4188587008Total Bytes Written :2009381888

Remember that statistics contained in the GV$ views are cumulative, so obtain samplesfrom the beginning and the end of a peak I/O cycle. Subtract the beginning statistics fromthe ending statistics to obtain true reads and true writes that have occurred. Use thisstatistic to determine the read-to-write ratios and to classify the database application mixand its workload type.


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Understanding the Application Mix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .


For instance, if the previously mentioned SQL was issued again in 10 minutes, that SQLmight have these statistics.

Number of Small Reads :500211

Number of Small Writes:123474Number of Large Reads :142981Number of Large Writes:8010Total Bytes Read :22232604961Total Bytes Written :5586081648

Calculate the IOPS for the small I/O and the large I/O, the percentage of reads to writes,and the MBps throughput. This calculation example uses the previous examples of output.

Small Read IOPS =(500211-205903)/(10*60) = 490 IOPSSmall Write IOPS =(123474-106883)/(10*60) = 27 IOPSTotal Small IOPS =(294308-16591)/(10*60) = 517 IOPS

I/O Percentage of Reads to Writes = 94:6

Large Read IOPS =(142981-40298)/(10*60) = 171 IOPSLarge Write IOPS =(8010-2791) /(10*60) = 8 IOPSTotal Large IOPS =(102683+5219) /(10*60) = 179 IOPSI/O Percentage of Reads to Writes = 96:4

Total MBPS Read =((22232604961-4188587008)/(10*60))/1048576=28 MBPSTotal MBPS Written =((5586081648-2009381888) /(10*60))/1048576=5 MBPSTotal MBPS =((18044017953+3576699760)/(10*60))/1048576=34 MBPS

Your actual numbers can help you determine performance and storage requirements.Obtain specifications from storage vendors or use various benchmarking tools such asOracle's Orion Workload tool to obtain them. By using the workload mix statistics andavailable specifications for your particular storage array, you can make informeddecisions.

If you see Oracle workloads that are near the specifications for your storage array,consider reconfiguration to allow for better IOPS or MBps.


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Chapter 3

Analyzing SQL

At the heart of every application is the underlying SQL. You can find many books andprocedures for determining troubleshooting and tuning SQL. As a start, consider usingOracle trace files and active sessions to find problematic SQL, applications, and users.You can use the information derived from trace files and active sessions to change eitherapplication behavior or user behavior to reduce the workload placed on a storage array.Use these tools to assist you in identifying objects in your database which are beingaccessed the most, and in segregating the objects to improve I/O activity.

Oracle TraceFor many years, database administrators have been getting low level tracing informationabout sessions by creating and reading Oracle-generated trace files. You can generate tracefiles against a full system load or individual sessions. Trace files provide this information:

SQL statements

Explain plans

Parse, run, and fetch counts

CPU and elapsed times

Physical reads and logical reads

Number of rows processed

Misses on the library cache

User name under which each parse occurred

Each commit and rollback

Wait event data

Row operations

Logical, physical and elapsed times I/O types

Although Oracle 10g provides a few mechanisms to trace the session by querying internalviews, the generation of trace files is still quite viable.


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Analyzing SQL. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .


Creating a Trace

Original Method

1 Use the DBM_SESSION.SQL_TRACE command. You must enter the commandthrough the connected session or application.

SQL> exec dbms_session.set_sql_trace(true);

2 Use the ALTER SESSION SET SQL_TRACE command. You must enter thecommand through the connected session or application.

SQL> ALTER SESSION SET SQL_TRACE = TRUE;

Newer Method Using DBMS_MONITOR PackageDBMS_Monitor is a robust package that allows starting a trace through a PL/SQLinterface and from outside the session or application. DBMS_MONITOR has the addedfeatures to trace on a set of various application specific environment variables that can beset within applications.

1 Determine the connected session or group of sessions that you would like to trace.Query the V$SESSION view with this SQL.

SQL> SELECT sid, serial#,client_identifier, service_name, action, module

FROM V$SESSION

2 Use the SID & SERIAL# column information to start a trace for a particular session.

SQL> EXECUTE DBMS_MONITOR.SESSION_TRACE_ENABLE(,,TRUE,TRUE);

Refer to the Oracle documentation site and read about the DBMS_MONITOR package:http://www.oracle.com/technology/software/tech/orion/index.html

Table 3-1 DBMS_MONITOR Package Variables

Session Variable Description

SID Identifier for the connected session.

SERIAL# Serial number of the connected.
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. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Creating a Trace


Generated Trace FilesWhen a trace file is generated, Oracle writes the file to a disk drive in an area that isdictated by the parameter USER_DUMP_DEST. To find the USER_DUMP_DEST areaon a disk drive, use one of two strategies:

Check the typical location, which is the $ORACLE_BASE/SID/udump directory onthe database server.

Run these commands:

SQL > show parameter user_dump_destSQL > select value from v$parameter where name ='user_dump_dest';

Use this syntax to run the TKPROF utility against a trace file and to then print a readablereport:

tkprof trace_file report_file

There are a several options to tkprof for providing various output characteristics:

Formatting all cryptic information into a more readable form

Breaking out each statement that was run during the trace period

Presenting various statistics for determining slow performance areas and where youmight spend time tuning application code

Generating an SQL script that allows you to store the captured statistics in a database

Determining the explain plan for that was run SQL statements

The tkprof utility provides a summary as well as detail information for collectedstatistics. The Oracle trace is a valuable tool for extracting statistics for a single session oracross a grouping of sessions. Oracle trace shows the current real-time activity for I/Opatterns and CPU activity. This is valuable information for determining the SQL causingperformance issues for placement of database objects across a storage array and for tuningan Oracle database based on those SQL commands.


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Analyzing SQL. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .


Active Sessions Active sessions is a set of SQL statements that you can use to help find active sessions thatare currently causing problems in the database. These SQL statements show all active

sessions but can easily be modified to find those sessions that are having particularproblems with I/O activities. As a database administrator you must to be able to detectwho is accessing the database and what SQL they are running so that you can develop astrategy to reconstruct the application or the storage arrays for better performance.

This paper presents only basic active session information. For detailed techniques andprocedures, see the Oracle documentation site and read about SQL tuning: http:// www.oracle.com/technology/software/tech/orion/index.html

Active sessions can provide such invaluable information as, what SQL is running withinthe Oracle engine, the SQL access path, and the true statistical values accumulated foreach run. Try these scripts, perhaps add to them, and you can begin to determine whatSQL is running within your environment.

V$SESSIONUse the V$SESSION to determine who is logged into the database and from a high leveloverview, what they are doing. Table 3-2 shows some of the important columns forobtaining this information.

Table 3-2 V$SESSION Columns

Column Description

SADDR Unique Oracle session address

SID Unique Oracle session

USERNAME Oracle user (same as from dba_users)

STATUS Status of the session. C heck for ACTIVE sessions that are runningSQL.

PROCESS Operating system process id for the connection. This information is givenonly as a reference for checking on the operating system side.

TYPE Type of session connected to the database

SQL_ADDRESS Address. Use this information with the SQL_HASH_VALUE columninformation to identify the SQL statement currently being ran.

SQL_HASH_VALUEHash value unique to the SQL statement. The SQL_HASH_VALUEcolumn is unique for a particular SQL statement regardless of whenit is run. Use this information with the SQL_ADDRESS columninformation to identify the SQL statement currently running.
http://www.oracle.com/technology/software/tech/orion/index.htmlhttp://www.oracle.com/technology/software/tech/orion/index.htmlhttp://www.oracle.com/technology/software/tech/orion/index.htmlhttp://www.oracle.com/technology/software/tech/orion/index.html


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. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Active Sessions


Run the following SQL statement to determine if the user is actually running SQL at thecurrent time:

select sid,to_char(logon_time,'MMDDYYYY:HH24:MI') logon_time,

username,type,status,process,sql_address,sql_hash_value

from v$sessionwhere username is not null

If a user has SQL that is running, the status column will be ACTIVE and the SQL_ADDR& SQL_HASH_VALUE will be populated.

V$SQLAREAOracle assigns a unique SQL_HASH_VALUE and SQL_ADDRESS to each SQLstatement. Join columns from V$SESSION and V$SQLAREA to determine who isrunning any current SQL. Table 3-3 shows some of the important columns for obtainingthis information from an SQL statement.

Table 3-3 V$SQLAREA Columns

Column Description

SQL_TEXTFirst 1000 characters of the SQL being run by the user. If you areconcerned with an SQL statement that is longer than 1000

characters, use V$SQL_TEXT which is described at V$SQLTEXT .OPTIMIZER_MODE Optimizer mode the query is using

ADDRESS Address to the parent of this cursor/SQL

HASH_VALUE Hash value to the parent statement in the library cache

CPU_TIME Accumulated microseconds of CPU time used by the SQL

ELAPSED_TIME Accumulated microseconds elapsed time used by the SQL

EXECUTIONS Total number of times this statement has been run

DISK_READS Total number of disk reads for all runs

DIRECT_WRITES Total number of direct writes for all run

BUFFER_GETS Total number of buffer gets for all run

ROWS_PROCESSED Total number of rows processed for all runs

SID Session identifier. Use this information along with the with information inthe SERIAL# column to identify a session and the objects that it uses.


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When Oracle runs a query, Oracle places the query in memory with a uniqueSQL_HASH_VALUE and the SQL_ADDRESS for each SQL statement. This allowsOracle to reuse the same SQL if needed by the running session at a latter date or byanother user.

The V$SQLAREA view gives you information on the amount of disk drive activitycaused by a particular SQL statement. Check for SQL statements that result in many reads

or writes but that process only a few rows of data. This pattern of activity can stress thestorage array and identify an area for improvement.

Use the following SQL statement to get the information on disk drive activity:

select session.sid,session.serial#,session.sql_id,session.sql_child_number,sesion.username,optimizer_mode,hash_value,address,cpu_time,elapsed_time,disk_reads,direct_writes,buffer_gets,rows_processed,sql_text

from v$sqlarea sqlarea, v$session sessionwhere session.sql_hash_value = sqlarea.hash_value

and session.sql_address = sqlarea.addressand session.username is not null

SERIAL# Serial number. Use this information along with the with information in theSID column to identify a session and the objects that it uses.

SQL_ID Identifier to the SQL currently running.

SQL_CHILD_NUMBER Child number of a SQL statement that is currently being ran

Table 3-3 V$SQLAREA Columns (continued)

Column Description


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DBMS_XPLAN ProcedureDBMS_XPLAN is a procedure that you can use to obtain a run plan of a currently runningSQL statement. To use DBMS_XPLAN, you only need to supply the SQL_ID andSQL_CHILD_NUMBER, from V$SESSION. DBMS_XPLAN will produce a formattedexplain output. Supply an SQL_ID and SQL_CHILD_NUMBER and then run this SQLstatement:

SELECT * FROMtable(DBMS_XPLAN.DISPLAY_CURSOR((''),));

From this SQL statement, you get the full explain output showing access paths, tables, andindexes being used. Take note of the ID column for each line of output. Use this output tofind the actual runtime statistics for that line of the explain plan.

This paper presents only basic tuning for Oracle applications. For detailed techniques andprocedures, see the Oracle documentation site and read about SQL tuning: http:// www.oracle.com/technology/software/tech/orion/index.html

V$SQL_PLAN_STATISTICSUse the V$SQL_PLAN_STATISTICS view to look at run statistics for an SQL statement.The limitation of using the V$SQLAREA view is that it is an accumulation of statistics fora particular SQL statement. If you need single-run statistics for an SQL statement, use theV$SQL_PLAN_STATISTICS view. There are columns in this view that report on the lasttime the statement was run. A real strength of this view is the actual statistics for each stepin the run plan through the OPERATION_ID column. Table 3-4 shows some of theimportant columns for obtaining this information from an active SQL statement

Table 3-4 V$SQL_PLAN_STATISTICS Columns

Column Description

ADDRESS Address to the parent of this cursor/SQL

HASH_VALUE Hash value to the parent statement in the library cache

PLAN_HASH_VALUE Plan hash value

OPERATION_ID Number for each step in the run plan

OUTPUT_ROWS Number of rows returned

LAST_CR_BUFFER_GETS Number of consistent gets for the last run of the plan for a given step

LAST_DISK_READS Number of physical disk reads for the last run of the plan for a given step
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Analyzing SQL. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .


Run the following SQL statement to obtain statistics:

select sesion.sid,sesion.username,sql_plan_statistics.operation_id Id,

sql_plan_statistics.last_output_rows Rows,sql_plan_statistics.last_cr_buffer_gets Consistent Gets,sql_plan_statistics.last_disk_reads Disk Reads

from v$sql_plan_statistics sql_plan_statistics, v$sessionsesion

where sesion.sql_hash_value = sql_plan_statistics.hash_valueand sesion.sql_address = sql_plan_statistics.addressand sesion.username is not null

V$SQLTEXTUse the V$SQL TEXT statement to view SQL statements longer than 1000 characters.

Table 3-5 shows some of the important columns in the V$SQLTEXT view:

Run the following SQL statement to view longer SQL text:

select sesion.sid,sql_text

from v$sqltext sqltext, v$session sesionwhere sesion.sql_hash_value = sqltext.hash_value

and sesion.sql_address = sqltext.addressand sesion.username is not null

order by sqltext.piece

Table 3-5 V$SQLTEXT Columns

Column Description

ADDRESSAddress to the parent of this cursor/SQL. Use this information along withthe HASH_VALUE to identify the SQL statement that is currentlyrunning.

HASH_VALUEHash value to the parent statement in the library cache. TheHASH_VALUE is unique for a particular SQL statement regardlessof when it runs.

PIECE Sequence number for piecing individual parts of SQL statement togetherSQL_TEXT Individual piece of SQL text


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. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Active Sessions


V$SESS_IOUse the V$SESS_IO view to determine if a query is responsive and actually doing work within the database. This command is useful if you have an active session and through theV$SESSION or V$SQLAREA views show a valid SQL statement that seems to be takingvery long. If the GETS, READS, or CHANGES columns continue to increase for asession, you can be certain that the SQL statement is responding. Table 3-6 shows some of the important columns in the V$SESS_IO view.

A simple join, linking of two tables, to the V$SESSION view gives you the results todetermine the I/O being run by active sessions. Use the following SQL statement to showthe V$SESS_IO view.

select sess_io.sid,sess_io.block_gets,sess_io.consistent_gets,sess_io.physical_reads,sess_io.block_changes,sess_io.consistent_changes

from v$sess_io sess_io, v$session sesionwhere sesion.sid = sess_io.sid

and sesion.username is not null

Table 3-6 V$SESS_IO

Column Description

SID Unique Oracle session. Use the Oracle session identifier (SID) to link back to the V$SESSION view for the active session.

BLOCK_GETS Number of block gets done

CONSISTENT_GETS Number of consistent gets done

PHYSICAL_READS Number of physical reads done

BLOCK_CHANGES Number of blocks that where changed

CONSISTENT_CHANGES Number of consistent block changes done


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Analyzing SQL. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .



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Chapter 4

Resource Contention

To address resource contention in Oracle, you must obtain information on the areas of slow performance in your system. Every application query must acquire resources such asdisk drives, locks, and memory calls to retrieve and alter information in database objects.When a database is improperly tuned, these resource begin to get over-used or the requestqueues for those objects becomes long. Processes must wait in a queue for a desiredresource. Oracle keeps track of these resource wait times and you can query for those waittimes through various SQL statements. You can then identify those resources that are mostwaited upon and tune the various parts of the database or application to make thoseresources more available. For storage array concerns, look for resources that are related toread, writes, any file, and the buffers that are used for reading and writing to disk drivefiles.

True Session Wait Activity in Oracle 10gThis chapter contains example sets of SQL statements for determining wait events, or poorresource usage within your database. These sets of SQL use the V$ACTIVE_SESSION_HISTORY view, which contains one row of sampled activity for each session that wasactive, either on the central processing unit or waiting for a resource. This new view inOracle 10g also contains sample data that was acquired through internal kernel code. Thedata is similar to the statistics seen in V$SESSION_WAIT, but has a limited amount of buffer space, about two megabytes per central processing unit. As this buffer gets full dueto the activity on the system, Oracle moves the captured statistics to disk drive. This moveis part of the Automatic Workload Repository (AWR) Snapshot mechanism, and thestatistics are then available through the DBA_HIST_ACTIVE_SESS_HISTORY view.Depending on the activity of the system, when querying for current information, youmight have to view both areas for a valid history. This is historical activity of the waits thathave occurred for SQL run. While you can view historical activity to find the true cause of poor performance, there are some limitations:

Because the statistics are stored in the rotating buffer and are moved only to the

DBA_HIST_ACTIVE_SESS_HISTORY view through a Snapshot, you may loosestatistics.

When the Snapshot mechanism (AWR) moves database statistics between theV$ACTIVE_SESSION_HISTORY view and theDBA_HIST_ACTIVE_SESS_HISTORY view, AWR only takes a sampling of the datain the V$ACTIVE_SESS_HISTORY view for the Snapshot.


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Resource Contention. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .


Because the AWR takes only a sampling of the data in theV$ACTIVE_SESS_HISTORY view, you must either get what you want in theV$ACTIVE_SESS_HISTORY view before a Snapshot or consider manually savingthe data elsewhere.

Resource Currently in High DemandYou can run an SQL query to get a list of the resources that were in high demand on yoursystem during the last 30 minutes. Look for those wait events that refer to reads, writes,files, or buffers. Investigate any activity that produced high wait times.

Run this SQL statement to check for high demand on resources:

select active_session_history.event,sum(active_session_history.wait_time +

active_session_history.time_waited) ttl_wait_timefrom v$active_session_history active_session_history

where active_session_history.sample_timebetween sysdate - 60/2880 and sysdategroup by active_session_history.eventorder by 2

What User is Waiting the Most

Sometimes one user or a group of users can cause databases process to stop suddenly. Youcan run an SQL query to determine usage. The results are for a single point in time,independent of the total resources that a user has used. Specifically, you can answer thesequestions:

What user is consuming the most resources.

Who is waiting the most for resources at a point in time.

If a user experiences delays, you can use this query to verify that the user is actuallywaiting in the database for a result set for a given time period.

Use this example statement to determine which user is waiting more often. This SQLstatement is written for a 30-minute interval, which can be adjusted, from the currentsystem time.

select sesion.sid,sesion.username,sum(active_session_history.wait_time +

active_session_history.time_waited) ttl_wait_timefrom v$active_session_history active_session_history,

v$session sesionwhere active_session_history.sample_time

between sysdate - 60/2880 and sysdateand active_session_history.session_id = sesion.sid

group by sesion.sid, sesion.usernameorder by 3


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. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . True Session Wait Activity in Oracle 10g


SQL Currently Using the Most ResourcesYou can run an SQL query to determine what SQL statement is consuming the mostresource wait times on your system. Another strategy is to use the V$SQLAREA view toidentify the top 10 or 20 SQL users on your system by disk drive reads or run.

The advantage of using this query is it that you can identify what SQL statements areconsuming resources and currently waiting the most.

select active_session_history.user_id,dba_users.username,sqlarea.sql_text,sum(active_session_history.wait_time +

active_session_history.time_waited) ttl_wait_timefrom v$active_session_history

active_session_history,v$sqlarea sqlarea,dba_users

where active_session_history.sample_timebetween sysdate - 60/2880 and sysdate

and active_session_history.sql_id = sqlarea.sql_idand active_session_history.user_id = dba_users.user_id

group by active_session_history.user_id,sqlarea.sql_text,dba_users.usernameorder by 4

What Object is Currently Causing the Highest Resource WaitsYou can run this query to see which objects a SQL statement is affecting. You can tailorthis query to report on the actual blocks that are being accessed within the objects for the

SQL statement. This helps you to determine if you need to reorganize your object orredistribute them to reduce the contention on that object.

Use an SQL statement like this to determine what object is currently causing the highestresource waits:

select dba_objects.object_name,dba_objects.object_type,active_session_history.event,sum(active_session_history.wait_time +

active_session_history.time_waited) ttl_wait_timefrom v$active_session_history active_session_history,

dba_objects

where active_session_history.sample_timebetween sysdate - 60/2880 and sysdate

and active_session_history.current_obj# =dba_objects.object_id

group by dba_objects.object_name,dba_objects.object_type,active_session_history.event

order by 4


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Resource Contention. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .



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Chapter 5

Conclusion

Tuning applications and the underlying storage array are critical to Oracle databaseperformance. Application and their connected sessions request information, whichinitiates requests for physical I/O with the storage array. By matching Oracle applicationrequirements, IOPS and MBps, to the abilities of a storage array you can improve both theapplication performance and the overall database system performance. Careful monitoringof the database and ultimately the applications that request the information on disk drivecan ensure improved performance from the storage array.

Gaining an understanding of the application mixture, determining the Oracle workloadand analyzing Oracle sessions are strategies that you can use to tune Oracle and theunderlying storage array.

Better tuning of the applications and storage array means improved performance formeeting the information needs of today and preparing for tomorrows needs.

Contact InformationFor more information and sales office locations, visit the LSI Logic web sites at:

http://www.lsi.com/cm/ContactSearch.do

North American Headquarters

Milpitas, CA

Tel: 866 574 5741 (within U.S), 408 954 3108 (outside U.S.)

LSI Logic KK Headquarters

Tokyo, Japan

Tel: 81 3 5463 7165

LSI Logic Europe Ltd. European Headquarters

United Kingdom

Tel: 44 1344 413200
http://www.lsilogic.com/cm/ContactSearch.dohttp://www.lsilogic.com/cm/ContactSearch.do


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Conclusion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .


ReferencesOracle Database Administrator's Guide 10g Release 2 (10.2)

Oracle Database Performance Tuning Guide 10g Release 2 (10.2)

Oracle Orion downloads

http://www.oracle.com/technology/software/tech/orion/index.html

Best Practices for Creating a Low-Cost Storage Grid for Oracle Databases

http://www.oracle.com/technology/deploy/availability/pdf/ora_lcs.pdf

Resilient Low-Cost Storage

http://www.oracle.com/technology/deploy/availability/pdf/lcs_OW.doc.pdf

Orion: Oracle I/O Numbers Calibration Tool

http://download.oracle.com/otn/utilities_drivers/orion/Orion_Users_Guide.pdf
http://www.oracle.com/technology/software/tech/orion/index.htmlhttp://www.oracle.com/technology/deploy/availability/pdf/ora_lcs.pdfhttp://www.oracle.com/technology/deploy/availability/pdf/lcs_OW.doc.pdfhttp://download.oracle.com/otn/utilities_drivers/orion/Orion_Users_Guide.pdfhttp://www.oracle.com/technology/deploy/availability/pdf/ora_lcs.pdfhttp://www.oracle.com/technology/deploy/availability/pdf/lcs_OW.doc.pdfhttp://download.oracle.com/otn/utilities_drivers/orion/Orion_Users_Guide.pdfhttp://www.oracle.com/technology/software/tech/orion/index.html


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Document DescriptionThis document providesinformation on tuning Oracle with consideration for storage and your applicationmix.

Ownership of MaterialsThe Document is provided as a courtesy to customers and potential customers of LSI Logic Corporation(LSI). LSI assumes no obligation to correct any errors contained herein or to advise any user of liabilityfor the accuracy or correctness of information provided herein to a user. LSI makes no commitment toupdate the Document. LSI reserves the right to change these legal terms and conditions from time to time atits sole discretion. In the case of any violation of these rules and regulations, LSI reserves the right to seek all remedies available by law and in equity for such violations. Except as expressly provided herein, LSI andits suppliers do not grant any express or implied right to you under any patents, copyrights, trademarks, ortrade secret information. Other rights may be granted to you by LSI in writing or incorporated elsewhere inthe Document.

Trademark AcknowledgmentsEngenio, the Engenio design, MegaRAID, HotScale, SANtricity, and SANshare are trademarks or registeredtrademarks of LSI Logic Corporation. All other brand and product names may be trademarks of theirrespective companies.

Performance InformationPerformance tests and ratings are measured using specific computer systems and/or components and reflectthe approximate performance of LSI products as measured by those tests. Any difference in systemhardware or software design or configuration may affect actual performance. Buyers should consult othersources of information to evaluate the performance of systems or components they want to purchase.


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