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ORACLE STATISTICS GATHERING STRATEGY

& VERSION CONTROL

By:

Yury Velikanov (Pythian)

& All of you

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Problem statement

•The most dangerous issue is … Dramatically changed performance

•What change performance? Application’s changes Statistics changes Data changes

•Version control Application Statistics Data

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Oracle Statistics gathering strategy

• How often do we need to gather statistics (if we need to gather it at all)

• What percentage should be used to gather statistics

• Should we lock statistics for any type of objects (staging tables, temporary tables etc)

• Partitioning and copying statistics from one partition to others

• Statistics gathering time windows and related techniques

• Automatic statistics gathering (pros/cons)

• Statistics gathering features in new Oracle RDBMS versions (11GR2)

• Statistics gathering and version control

• Do we still need to use analyse command as alternative to dbms_stats?

• Stats and DEV/TEST/UAT environment. How to manage those?

• Statistics gathering performance

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How often ?

•Never

•Each 24 hours

•Each SQL run

•Weekly/Monthly/Yearly

•AUTO MAGICALLY :)

•Important!

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What % gather statistics ?

•100% all the time

•10% all the time

•AUTO

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Should we lock statistics

•staging tables

•temporary tables

•tables that we don’t want application to gather statistics itself

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Stats and Huge Tables

•Partitioning Could copying statistics from one older to new partition

•Huge table Why we should gather statistics at all :)

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Statistics gathering performance•Parallel option!

•Memory settings!

•Do not gather stats there where we do not need it

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Universal statistics gathering

•Statistics gathering time windows and related techniques

•Automatic statistics gathering (pros/cons)

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Statistics gathering features in new Oracle RDBMS versions (11GR2) •http://www.articles.freemegazone.com/11g-enhanced-optimizer-statistics-maintenance.php

•Setting STALE_PERCENT per Object

•Pending Statistics (gather but not publish)

•Extended Statistics (multi columns)

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Statistics & version control

•This is close to perfect strategy

•It doesn't address the problem for 100% There are always changes in the application There are always changes in the date

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Do we still need to use analyse command as alternative to dbms_stats?

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Stats and DEV/TEST/UAT environment. How to manage those?

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Best practices

•Save previous statistics before gathering a new one

•Gather statistics rare as possible

•Manage exceptions Lock statistics

•Test changes in the statistics gathering approuch