11g SQL Performance Analyzer and Tuning Features Oracle 11g New Features Tips by Burleson Consulting July 13, 2008

Oracle 11g SQL New Features Tips

Oracle 10g introduced several major performance enhancements, many of them in the form of advisors and automatic features.  The new analysis available with 10g allowed a Remote DBA to locate the root cause of their performance issues and drill down into waits and bottlenecks.  Those abilities have been enhanced in Oracle 11g, using analytic data built into the AWR in new ways.

For instance, many of the performance features of Oracle 10g allowed reactive analysis, and limited forecasting and proactive tuning.  Oracle 11g introduces new tools that allow full-scale proactive tuning, maintenance, and testing.  One of the most comprehensive tools available for 11g that assists with all three of these goals is the SQL Performance Analyzer.

A trip to the SPA – Inside the 11g SQL Performance Analyzer

The declarative nature of the SQL syntax has always made it difficult to perform SQL tuning.  The basic tenet of cost-based SQL optimization is that the person who writes a SQL query simply "declares" what columns they want to see (the SELECT clause), the tables where the columns reside (the FROM clause), and the filtering conditions (the WHERE clause).   It's up to the SQL optimizer to always determine the optimal execution plan.  This is a formidable challenge, especially in a dynamic environment, which is why Oracle introduced the 10g new feature of CBO dynamic sampling. 

Oracle tuning consultants have known for many years that the best way to tune an Oracle system is to take a top-down approach, finding the optimal configuration for external factors (i.e. OS kernel settings, disk I/O subsystem), and determining the best overall setting for the Oracle instance (i.e. init.ora parameters). 

Holistic tuning involves tuning a representative workload, adjusting global parameters in order to optimize as much SQL as possible.  Only then, is it prudent to start tuning individual SQL statements.  Many Oracle professional who adopt a bottom-up approach (tune the SQL first), find all of their hard-work un-done when a change is made to a global setting, such as one of the SQL optimizer parameters or recomputing optimizer statistics. 

Oracle’s holistic SQL tuning approach is new, and given the misleading marketing name "fully automated SQL tuning".  Holistic tuning is well-known to working Remote DBA's who have been doing manual workload-based optimization since Oracle 6.  Now in 11g, Oracle gives us an automated method.

The Oracle 11g SQL Performance Analyzer (SPA), is primarily designed to speed up the holistic SQL tuning process, automating much of the tedium.

Once you create a workload (called a SQL Tuning Set, or STS), Oracle will repeatedly execute the workload, using sophisticated predictive models (using a regression testing approach) to accurately identify the salient changes to execution plans, based on your environmental changes.

Using SPA, we can predict the impact of system changes on a workload, and we can forecast changes in response times for SQL after making any change, like parameter changes, schema changes, hardware changes, OS changes, or Oracle upgrades; any change that influence SQL plans is a good candidate for SPA.

 

This is an excerpt from the new book Oracle 11g New Features: Expert Guide to the Important New Features by John Garmany, Steve Karam, Lutz Hartmann, V. J. Jain, Brian Carr. You can buy it direct from the publisher for 30% off.