SOM Sponsors: ORACLE STATISTICS GATHERING STRATEGY & VERSION CONTROL By: Yury Velikanov (Pythian) & All of you

SOM Sponsors: Problem statement The most dangerous issue is … ­Dramatically changed performance What change performance? ­Applications changes ­Statistics changes ­Data changes Version control ­Application ­Statistics ­Data

SOM Sponsors: 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

SOM Sponsors: How often ? Never Each 24 hours Each SQL run Weekly/Monthly/Yearly AUTO MAGICALLY :) Important!

SOM Sponsors: What % gather statistics ? 100% all the time 10% all the time AUTO

SOM Sponsors: Should we lock statistics staging tables temporary tables tables that we dont want application to gather statistics itself

SOM Sponsors: Stats and Huge Tables Partitioning ­Could copying statistics from one older to new partition Huge table ­Why we should gather statistics at all :)

SOM Sponsors: Statistics gathering performance Parallel option! Memory settings! Do not gather stats there where we do not need it

SOM Sponsors: Universal statistics gathering Statistics gathering time windows and related techniques Automatic statistics gathering (pros/cons)

SOM Sponsors: Statistics gathering features in new Oracle RDBMS versions (11GR2) enhanced-optimizer-statistics-maintenance.phphttp:// enhanced-optimizer-statistics-maintenance.php Setting STALE_PERCENT per Object Pending Statistics (gather but not publish) Extended Statistics (multi columns)

SOM Sponsors: 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

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

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

SOM Sponsors: 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