James F. Koopmann Implications of Setting Oracle9iR2’s Statistics Collection Level 1 Implications of Setting Oracle9iR2’s Statistical Collection Level

James F. Koopmann

Implications of Setting Oracle9iR2’s Statistics Collection Level 1

Implications

of Setting

Oracle9iR2’s

Statistical Collection LevelJames F. Koopmann

Co-Founder & Chief Architect

dbDoctor Inc.

Colorado

[email protected]

[email protected]

James F. Koopmann


Content

1. Why statistics are important, Who Needs them ?

2. What is the new method of setting up statistical collections.

3. How you can see what your settings are currently

4. How you can change your settings.

5. A test scenario for determining system impact of collecting statistics.

6. SPFILE Usage

7. Various Examples

8. Information exchange

James F. Koopmann


Why Do We Care About Statistics, Who Needs Them

TRUE or FALSE

Collecting Statistics

will

make my

database run faster

James F. Koopmann



TRUE or FALSE

Collecting Statistics

will in the future

make my

database run faster

James F. Koopmann



It’s All About Problem Detection

What Are Problems?1. Problems are anything that causes us, or our database discomfort.

2. Problems are anything that occurs in relation to the database that is a deviation from the norm.

A few questions to ask yourself1. If a batch job runs one hour longer than normal, is it a problem if no one knows about it?

2. If you take down the listener and no one tries to connect to your database, is it a problem?

3. If the database is down and isn’t being used, is it a problem?

James F. Koopmann



It’s All About Problem Detection

Lazy man method of finding problemsa. You can find problems by snooping around in the database

b. You can find problems from user complaints

c. You can find problems when the system crashes or is unavailable

d. Use of rudimentary statistics (wall clock, system feel)

Intelligent method of finding problemsa. Realizes that aggregate statistics aren’t enough

b. Has a method of detecting change, where have I been and where am I going.

c. Hard and fast statistics (V$ tables, iostat, vmstat, …).

James F. Koopmann



The Problem with Problems1. We have to fix them

2. Mistakes are common and we can’t rid ourselves of thema. Be compassionate

b. Be humble

3. Receive new ideas with an open but analytical minda. Research for yourself

b. Have reliable sources

4. Validate what you have heard or reada. don’t take for granted everything you read or hear

b. “Your mileage may vary”

5. Accept only after validationa. This is the best part, you can count on what you have learned

b. You can use new knowledge to validate other scenarios

James F. Koopmann


New to Oracle9iR2

STATISTICS_LEVEL

Controls Collection of Advisories and Statistics

1. Shared Pool Advice2. Buffer Cache Advice3. PGA Advice4. MTTR Advice5. Segment Level Statistics6. Timed Statistics7. Timed OS Statistics8. Plan Execution Statistics

James F. Koopmann


DYNAMICParameter can be modified using the ALTER SESSION or ALTER SYSTEM statement while an instance is

running.

Syntax we are all familiar with

ALTER SESSION SET parameter_name = value 1. Change the value of a parameter for the duration of the session.

2. The value of this parameter does not change for other sessions in the instance.

ALTER SYSTEM SET parameter_name = value 1. Change the value of the parameter for all current and future sessions.

2. Record the change in the alert.log

ALTER SYSTEM SET parameter_name = value [DEFERRED] 1. Change only applies to future sessions that will connect to the database.

2. Record the change in the alert.log

STATISTICS_LEVEL is a Dynamic Parameter

New to Oracle9iR2

James F. Koopmann


New to Oracle9iR2

V$STATISTICS_LEVELColumn Values(?) Description

STATISTICS_NAME Name of the statistics/advisory.

DESCRIPTION Description of what the statistics/advisory does and

what it can be used for.

SESSION_STATUS ENABLED|DISABLED Status of the statistics/advisory for this session.

SYSTEM_STATUS ENABLED|DISABLED Status of the statistics/advisory system-wide.

ACTIVATION_LEVEL BASIC|TYPICAL|ALL Indicates the level of STATISTICS_LEVEL than enable

this statistics/advisory

STATISTICS_VIEW_NAME If there is a single view externalizing this

statistics/advisory, the name of that view.If there is

no such a view, this column is empty. If there are

multiple views involved, the DESCRIPTION column should

mention the view names.

SESSION_SETTABLE YES|NO. Whether this statistics/advisory can be set at the

session level.

James F. Koopmann


New to Oracle9iR2

V$STATISTICS_LEVELSQL> SELECT statistics_name, statistics_view_name, description FROM v$statistics_level

STATISTICS_NAME STATISTICS_VIEW_NAME DESCRIPTION

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

Shared Pool Advice V$SHARED_POOL_ADVICE Predicts the impact of different values of

shared_pool_size on elapsed parse time saved

PGA Advice V$PGA_TARGET_ADVICE Predicts the impact of different values of

pga_aggregate_target on the performance of

memory intensive SQL operators

Segment Level Statistics V$SEGSTAT Enables gathering of segment access statistics

Timed OS Statistics Enables gathering of timed operating system

statistics

MTTR Advice V$MTTR_TARGET_ADVICE Predicts the impact of different MTTR settings

on number of physical I/Os

Buffer Cache Advice V$DB_CACHE_ADVICE Predicts the impact of different cache sizes on

number of physical reads

Timed Statistics Enables gathering of timed statistics

Plan Execution Statistics V$SQL_PLAN_STATISTICS Enables collection of plan execution statistics

James F. Koopmann


1. Simplified Parameter Management

2. Change in STARTUP Sequence

3. Push to Migrate from Parameter File

SPFILE

Is the Init.ora File Going Away ?

James F. Koopmann


SQL> show parameter spfile

NAME TYPE VALUE

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

spfile string

SPFILE

DO You Have One?

James F. Koopmann


SPFILE

How Do I Get One?

Help, I Want My INIT.ORA

James F. Koopmann


• Must be SYSOPER or SYSDBA to create one• Occasionally save you SPFILE• SPFILE is a binary file• SHUTDOWN / STARTUP to recognize• ORA-12547: TNS:lost contact• ALTER SYSTEM RECOGNIZE command

SPFILE

Items to Consider

James F. Koopmann


SPFILE

Setting a Parameter

ALTER SYSTEM SET

DEFERRED, changes the value for the parameter for sessions connecting after the statement is issued.

SCOPE, specifies when the change will take effect.1. MEMORY - the change takes effect immediately but is not available after

next startup2. SPFILE - the change is made in the server parameter file only and

available after next startup3. BOTH - MEMORY + SPFILE, this is the default

James F. Koopmann


SPFILE

ALTER SYSTEM RESET

Resetting a Parameter

Switch to default statistics_level alter system set statistics_level=typical scope=memory;

alter system reset statistics_level scope=spfile sid=‘*’;

Switch timed_statistics to be under statistics_level controlalter system set timed_statistics=true scope=memory;

alter system reset timed_statistics scope=spfile sid=‘*’;

James F. Koopmann


SPFILE

Setting a Parameter that is a List of Strings

alter system set control_files=

'/u01/app/oracle/oradata/saigon/control01.ctl',

'/u01/app/oracle/oradata/saigon/control02.ctl',

'/u01/app/oracle/oradata/saigon/control03.ctl'

scope=spfile;

James F. Koopmann


STATISTICS_LEVEL

Parameter ALTER SESSION

ALTER SYSTEM

ALTER SYSTEM …DEFERRED

STATISTICS_LEVEL

Db_cache_advice

Timed_statistics

Timed_os_statistics

Dynamic Parameters

James F. Koopmann


STATISTICS_LEVEL

Statistic / Advisory BASIC TYPICAL ALL SESSION SPFILE

Shared Pool Advice

Buffer Cache Advice db_cache_advice

PGA Advice

MTTR Advice

Segment Level Statistics

Timed Statistics timed_statistics

Timed OS Statistics timed_os_statistics

Plan Execution Statistics

Three Settings Override

James F. Koopmann


SQL> SELECT name, value, isses_modifiable,

issys_modifiable,isdefault,ismodified

FROM v$parameter

WHERE NAME IN ('statistics_level','db_cache_advice', 'timed_statistics', 'timed_os_statistics');

NAME VALUE ISSES_MODIFIABLE ISSYS_MODIFIABLE ISDEFAULT ISMODIFIED

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

timed_statistics FALSE TRUE IMMEDIATE TRUE FALSE

timed_os_statistics 0 TRUE IMMEDIATE TRUE FALSE

db_cache_advice OFF FALSE IMMEDIATE TRUE FALSE

Take a Look at Your Settings

Override Control (V$PARAMETER)

statistics_level TYPICAL TRUE IMMEDIATE TRUE FALSE

TRUE = Default Value

(NO SPFILE entry)

FALSE = SPFILE entry

FALSE = Not Modified since startup

MODIFIED = ALTER SESSION

SYSTEM_MOD = ALTER SYSTEM

James F. Koopmann


SQL> SELECT statistics_name, session_status, system _status

activation_level, session_settable

FROM v$statistics_level


Override Control (V$STATISTICS_LEVEL)

STATISTICS SESSION SYSTEM ACTIVATION SESSION

NAME STATUS STATUS LEVEL SETTABLE

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

Buffer Cache Advice ENABLED ENABLED TYPICAL NO

MTTR Advice ENABLED ENABLED TYPICAL NO

PGA Advice ENABLED ENABLED TYPICAL NO

Segment Level Statistics ENABLED ENABLED TYPICAL NO

Shared Pool Advice ENABLED ENABLED TYPICAL NO

Timed Statistics ENABLED ENABLED TYPICAL YES

Plan Execution Statistics DISABLED DISABLED ALL YES

Timed OS Statistics DISABLED DISABLED ALL YES

What Level in STATISTICS_LEVEL

to ActivateAm I CollectingAm I Collecting

James F. Koopmann


• If there is an entry in SPFILE then setting STATISTICS_LEVEL will not have an impact on that statistic or advisory.

• Even if the setting in the SPFILE is the DEFAULT, it will still not be under the control of the STATISTICS_LEVEL parameter.

• When looking at v$parameter and v$statistics_level after you have made changes, you may get confused.

• ALTER SYSTEM command will override any ALTER SESSION command

• RESET any parameters that you want to be controlled by the new STATISTICS_LEVEL parameter.


Don’t Get Confused

James F. Koopmann


The setting of timed_os_statistics to anything other than 0 (zero) or 5 will switch the SESSION_STATUS & SYSTEM_STATUS in V$STATISTICS_LEVEL to UNKNOWN


Oracle Gets Confused

NAME VALUE ISSES_MODIFIABLE ISSYS_MODIFIABLE ISDEFAULT ISMODIFIED

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

timed_os_statistics 10 TRUE IMMEDIATE FALSE FALSE

STATISTICS SESSION SYSTEM ACTIVATION SESSION

NAME STATUS STATUS LEVEL SETTABLE

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

Timed OS Statistics UNKNOWN UNKNOWN ALL YES

James F. Koopmann


Human Impact

The Most Hated Statements 1. You must set TIMED_STATISTICS to TRUE

in the parameter file.

2. I recommend using timed statistics.

3. Doing this will have a small negative effect on system performance.

4. You will incur minimal resource overhead

5. You cannot afford to be without the information that timed statistics provides.

6. Gathering OS statistics is very expensive.

James F. Koopmann


Human Impact

Typical Responses

1. Sorry, Oracle Support does not have any specific benchmark information.

2. Contact ___________, they may have benchmark information.

3. Can anyone else share their input and experiences.

4. My Technical Consultant has not seen any specific benchmarks on this.

5. Take a look at the guide and if necessary we will try to get some development resources

James F. Koopmann


System Impact

Statistic / Advisory BASIC TYPICAL ALL

Shared Pool Advice

Buffer Cache Advice

PGA Advice

MTTR Advice

Segment Level Statistics

Timed Statistics

Timed OS Statistics

Plan Execution Statistics

Test Scenarios 1. Reduce stress

associated with statistical collection

2. Who else will help

3. Validate for myself

Why

James F. Koopmann


System Impact

Basic Terminology

User / Job

Request

(workload)

(v$sysstat)

User

Decides

What to

Do Next

Database

Completes

Request

Database Response Time

Coffee Break

Throughput

Resource Usage

(v$sysstat)

Sorts, Reads, Writes, Enqueues, Redo activity, Buffer cache activity, Parsing,

…

User

Queues

Next

Transaction

Think

Time

LGWR wait for redo copy,

log file sync,

db file sequential read,…

Wait Times

(v$system_event)

James F. Koopmann


System Impact

Test Scenarios (workload types)

execute count, Total number of calls (user and recursive) that executed SQL statements

calls to get snapshot scn: kcmgss, Number of times a snapshot system change number (SCN) was allocated. The SCN is allocated at the start of a transaction.

session logical reads, The sum of db_block_gets and consistent_gets.

db block gets, Number of times a CURRENT block was requested

consistent gets, Number of times a consistent read was requested for a block.

db block changes, This statistic counts the total number of changes that were part of an update or delete operation that were made to all blocks in the SGA. This approximates total database work. It statistic indicates the rate at which buffers are being dirtied.

user commits, Number of user commits. When a user commits a transaction, the redo generated that reflects the changes made to database blocks must be written to disk. Commits often represent the closest thing to a user transaction rate.

James F. Koopmann


System Impact

Test Scenarios (workload types) Statistic BASIC

timed_statisticsTYPICAL

TYPICAL / BASIC

ALL

ALL / TYPICAL ALL / BASIC

execute count 520370 505683

(2.82%)

498753

(1.37%)

4.15%

calls to get snapshot scn: kcmgss

703731 682467

(3.02%)

674396

(1.18%)

4.17%

session logical reads 1087327 1052570

(3.20%)

1041518

(1.05%)

4.21%

db block changes 446278 431281

(3.36%)

427297

(0.92%)

4.25%

user commits 39405 38323

(2.75%)

37766

(1.45%)

4.16%

James F. Koopmann


System Impact

Test Scenarios (wait types)Statistic BASIC

timed_statisticsTYPICAL

TYPICAL / BASIC

ALL

ALL / TYPICAL ALL / BASIC

Total Waits 44451 42719

(3.90%)

42558

(.38%)

(4.26%)

Total Timeouts 40584 39272

(3.23%)

38859

(1.05%)

(4.25%)

Total Time Waited 682 634

(7.04%)

655

(-3.31%)

(3.96%)

James F. Koopmann


System Impact

Test Scenarios (resource types)Statistic BASIC

timed_statistics

TYPICAL ALL TYPICAL / BASIC ALL / TYPICAL

ALL / BASIC

redo blocks written 146059 141432 139607 3.17% 1.29% 4.42%

redo entries 224570 216854 214942 3.44% 0.88% 4.29%

redo size 68865028 66699016 65852920 3.15% 1.27% 4.37%

redo writes 40685 39394 38970 3.17% 1.08% 4.22%

change write time 1238 1227 1221 0.89% 0.49% 1.37%

enqueue requests 143264 137748 137173 3.85% 0.42% 4.25%

enqueue waits 8 33 20 -312.50% 39.39% -150.00%

consistent changes 7162 6460 6833 9.80% -5.77% 4.59%

physical reads 3210 2778 3116 13.46% -12.17% 2.93%

physical writes 3297 2946 3040 10.65% -3.19% 7.79%

parse count (total) 4818 4545 4680 5.67% -2.97% 2.86%

sorts (memory) 1937 1830 1885 5.52% -3.01% 2.68%

sorts (rows) 4251 4244 4243 0.16% 0.02% 0.19%

table fetch by rowid 11975 11041 11505 7.80% -4.20% 3.92%

table scan blocks gotten 85358 82778 81920 3.02% 1.04% 4.03%

table scan rows gotten 400388 386772 383741 3.40% 0.78% 4.16%

table scans (long tables) 17 16 17 5.88% -6.25% 0.00%

table scans (short tables) 122229 118631 117138 2.94% 1.26% 4.17%

James F. Koopmann


System Impact

More Data

Give Me a Call

file:///C:/temp/Vsysstat.htm

file:///C:/temp/Vsysstat_xls.htm

file:///C:/oradoc/920doc/server.920/a96536/apc2.htm

James F. Koopmann


Buffer Cache Advisory

Why: Disk is slow, memory is fast

What: Use to size the buffer caches

When: Performance is bad

Where: Populates V$DB_CACHE_ADVICE for each buffer cache in use

(2K, 4K, 8K, 16K, 32K, KEEP, RECYCLE)

How: db_cache_advice / statistics_level

Defined

James F. Koopmann



A Tried and True FriendCalculate Buffer Cache Hit Ratio

SQL> SELECT name, block_size,

100*(1 - (physical_reads / (db_block_gets+consistent_gets))) buffhit

FROM v$buffer_pool_statistics;

How we size the buffer cache

1. Just issue the SQL to see the hit ratio

2. Got smarter and diff’d between a start and end time

3. Run a valid workload through system

4. Come up with a ballpark estimate on size

5. Increase buffer cache if hit ratio is low

6. Done if hit ratio is high

James F. Koopmann



Diff’d Buffer Cache Hit RatioSQL> SELECT b.name, b.block_size,

100*(1 - ((e.physical_reads-b.physical_reads) /

((e.db_block_gets-b.db_block_gets)+

(e.consistent_gets-b.consistent_gets)))) buffhit

FROM beg_buffer_pool_statistics b, end_buffer_pool_statistics e

WHERE b.name=e.name AND b.block_size=e.block_size;

How to diff

1. Create table beg_buffer_pool_statistics as select * from v$buffer_pool_statistics

2. Run workload through system

3. Create table end_buffer_pool_statistics as select * from v$buffer_pool_statistics

4. Issue above SQL

James F. Koopmann



Use of V$DB_CACHE_ADVICESQL> SELECT name, block_size, size_for_estimate,

estd_physical_read_factor, estd_physical_reads

FROM V$DB_CACHE_ADVICE

WHERE advice_status = 'ON';

How to get the statistics

1. Set db_cache_advice to ‘READY’

2. Set db_cache_advice to ‘ON’

3. Run a valid workload through system

4. Issue above SQL

James F. Koopmann



Output of V$DB_CACHE_ADVICE BLOCK Cache Estd Phys Estd PhysNAME SIZE Size Read Factor Reads-------- ----- ----- ----------- ----------DEFAULT 8192 48 2.1133 343669940DEFAULT 8192 96 1.7266 280783364DEFAULT 8192 144 1.4763 240091867DEFAULT 8192 192 1.3573 220733606DEFAULT 8192 240 1.2801 208181172DEFAULT 8192 288 1.2165 197842182DEFAULT 8192 336 1.1686 190052917DEFAULT 8192 384 1.1202 182180544DEFAULT 8192 432 1.0877 176884743DEFAULT 8192 480 1.0602 172420984DEFAULT 8192 528 1.0196 165812231DEFAULT 8192 544 1 162626093DEFAULT 8192 576 .9765 158797352DEFAULT 8192 624 .9392 152735392DEFAULT 8192 672 .9216 149879874DEFAULT 8192 720 .9013 146571255DEFAULT 8192 768 .885 143928671DEFAULT 8192 816 .8726 141908868DEFAULT 8192 864 .8607 139972381DEFAULT 8192 912 .8492 138098490DEFAULT 8192 960 .8277 134610328

DEFAULT 8192 544 1.00 162626093 CURRENT

Its all about reads1. Don’t reduce the size of

your cache if you are going to incur more physical reads

2. Don’t increase the size of your cache if you are not going to reduce the number of reads

James F. Koopmann


&CommentsConcernsQuestionsAnswers

DosDon’ts

James F. Koopmann


Implications

of Setting

Oracle9iR2’s

Statistical Collection LevelJames F. Koopmann

dbDoctor Inc.

Colorado

[email protected]

[email protected]

Documents

James F. Koopmann Implications of Setting Oracle9iR2’s Statistics Collection Level 1 Implications of Setting Oracle9iR2’s Statistical Collection Level