This document provides an overview of SQL tuning in Oracle 10g using the SQL Tuning Advisor and SQL Access Advisor. It describes the challenges of manual SQL tuning and how the advisors automate the tuning process. The SQL Tuning Advisor analyzes SQL statements, statistics, and access paths to recommend optimizations like indexes, SQL profile changes, and statistics gathering. The SQL Access Advisor recommends comprehensive index and materialized view strategies for a workload. The document outlines how to use the advisors through the Oracle Enterprise Manager interface or PL/SQL APIs and provides best practices for live and remote SQL tuning.

2. SQL Tuning in Oracle 10g:
The Do’s and Don’ts
Mughees A. Minhas
Group Product Manager
Database Manageability
Oracle Corp.

3. Outline
y Introduction
y Manual Tuning Challenges
y SQL Tuning & Access Advisor Overview
y SQL Tuning Advisor
– Automatic SQL Tuning
– Usage scenarios
– User interface
y SQL Access Advisor
– Usage scenarios
– User interface
y Tips, Do’s, Don’ts
y Conclusion

4. Introduction
y Automatic SQL Tuning solution consists of
– SQL Tuning Advisor
– SQL Access Advisor
y Provides comprehensive, automatic, and cost-
effective solution for application tuning
y Reduces SQL tuning time by up to 80%
y Reduces management cost

5. Manual Tuning Challenges
y Requires expertise in several domains
– SQL optimization: adjust the execution plan
– Access design: provide fast data access
– SQL design: use appropriate SQL constructs
y Time consuming
– Each SQL statement is unique
– Potentially large number of statements to tune
y Never ending task
– SQL workload always evolving
– Plan regressions

6. Manual Tuning Example
Packaged App Tuning Scenario
Manual Tuning
1. Get explain plan
2. Examine query objects and their sizes
3. Review and compare explain plan statistics with execution
statistics (stored in V$SQL view)
4. Identify the problem, e.g., “first rows” issue because only recent
data is ever displayed despite large history being queried
5. Contact application vendor
6. Produce test case for vendor
7. Get a patch with appropriate code modifications from the
vendor
8. Install the patch in next maintenance cycle

7. SQL Tuning & Access Advisor
Overview
How do I tune
my SQL
workload?
SQL Tuning &
Access Advisors
Solution
Component
of CBO
Provides
implementation
script
No expert
required
DBA
SQL
Workload

8. SQL Tuning Advisor

9. Oracle 10g Automates the SQL
Tuning Process
I can do it
for you !
SQL Tuning
Advisor
DBA
High-Load
SQL
ADDM
SQL
Workload

10. Automatic SQL Tuning Overview
Add Missing
Indexes
Modify SQL
Constructs
Create a SQL
Profile
Automatic Tuning Optimizer
SQL Structure
Analysis
Access Path
Analysis
SQL
Profiling
Statistics
Analysis
Gather Missing or
Stale Statistics
DBA
SQL Tuning
Recommendations
SQL Tuning
Advisor

11. Automatic Tuning Optimizer (ATO)
y It is the query optimizer running in tuning mode
– Uses same plan generation process but performs
additional steps that require significantly more time
y It performs verification steps
– To validate statistics and its own estimates
y Uses dynamic sampling and partial executions to validate
y It performs exploratory steps
– To investigate the use of new indexes that could
provide significant speed-up
– To analyze SQL constructs that led to expensive
plan operators

12. Statistics Analysis
Add Missing
Indexes
Modify SQL
Constructs
Create a SQL
Profile
Automatic Tuning Optimizer
SQL Structure
Analysis
Access Path
Analysis
SQL
Profiling
Statistics
Analysis
Gather Missing or
Stale Statistics
DBA
SQL Tuning
Recommendations
SQL Tuning
Advisor

13. Statistics Analysis
y Motivation
– Statistics are key input to the query optimizer
y Their availability and accuracy is very important
y In Oracle10g, the Automatic Statistics
Collection maintains statistics up to date…
– But it may not be enabled or properly configured!
y The ATO verifies statistics that it needs/uses
– Generates auxiliary information to compensate for
missing or stale statistics
– Generates recommendations to gather statistics
where appropriate

14. SQL Profiling
Add Missing
Indexes
Modify SQL
Constructs
Create a SQL
Profile
Automatic Tuning Optimizer
SQL Structure
Analysis
Access Path
Analysis
SQL
Profiling
Statistics
Analysis
Gather Missing or
Stale Statistics
DBA
SQL Tuning
Recommendations
SQL Tuning
Advisor

15. SQL Profiling
y Motivation
– Empower query optimizer to find better plan by
gathering additional information on query behavior
y The query optimizer has time constraints
– Makes compromises while finding right plan
y The ATO is allowed a lot more time
– Uses the time to gather customized information
about the SQL statement, known as SQL Profile
– Builds a SQL Profile and recommends it
– Once implemented, SQL Profile is used by the
query optimizer to generate a well-tuned plan

16. SQL Profile
y Contains auxiliary information collected by the
ATO for a SQL statement
– Customized optimizer settings
y Based on past execution history (e.g., first_rows vs. all_rows)
– Compensation for missing or stale statistics
– Compensation for errors in optimizer estimates
y Estimation errors occur due to data skews and correlations,
complex filters and joins
y Doesn’t require any change to the SQL text
– Ideal for Packaged Apps
y Persistence: Works across shutdowns & upgrades
y Transportable across databases (10.2)

17. SQL Profiling Flow
Optimizer
(Tuning Mode)
create
submit
SQL Profiling
Optimizer
(Normal Mode)
output
submit
SQL
Profile
SQL Tuning
Advisor
Database
Users
Well-Tuned
Plan
After …
use

18. Access Path Analysis
Add Missing
Indexes
Modify SQL
Constructs
Create a SQL
Profile
Automatic Tuning Optimizer
SQL Structure
Analysis
Access Path
Analysis
SQL
Profiling
Statistics
Analysis
Gather Missing or
Stale Statistics
DBA
SQL Tuning
Recommendations
SQL Tuning
Advisor

19. Access Path Analysis
y Motivation
– Adding an index may significantly improve the
performance of a SQL statement
y Problem: A critical access path is missing
– Index not created or mistakenly dropped
y ATO explores the use of new indexes
– Recommends index if major performance boost
provided
– Also recommends running SQL Access Advisor to get
comprehensive index analysis for entire workload
y SQL Access Advisor also uses this analysis mode

20. SQL Structure Analysis
Add Missing
Indexes
Modify SQL
Constructs
Create a SQL
Profile
Automatic Tuning Optimizer
SQL Structure
Analysis
Access Path
Analysis
SQL
Profiling
Statistics
Analysis
Gather Missing or
Stale Statistics
DBA
SQL Tuning
Recommendations
SQL Tuning
Advisor

21. SQL Structure Analysis
y Motivation
– Help application developers identify poorly written
SQL statements
– Suggest restructuring of SQL for efficiency
y Problem categories
– Semantic changes of SQL operators (e.g., use
UNION ALL instead of UNION)
y Subject to user acceptance of new result
– Syntactic changes to predicates on indexed columns
(e.g., remove type mismatch in column = :bind)
– SQL design issues (e.g., add missing join predicate
to eliminate a large Cartesian join)

22. SQL Tuning Usage Scenarios
SQL Tuning
Advisor
ADDM High-load SQL
Cursor Cache
AWR
SQL Tuning Set
(STS)
User-defined
Filter / Rank
SQL Sources Manual Selection
Automatic Selection
AWR

23. SQL Tuning Set (STS)
y Motivation
– Enable user to tune custom set of SQL statements
y New object in Oracle10g for capturing and
managing SQL workload
y Stores SQL statements along with:
– Execution context: parsing user, bind values, etc.
– Execution statistics: buffer gets, CPU time, elapse
time, number of executions, etc.
y Transportable across databases (10.2)
y Created from any SQL source
– AWR, cursor cache, user-defined workload, STS

24. SQL Tuning Set Benefits
y Allows selective, on-demand, custom SQL
workload tuning
y Simplifies tuning of large number of SQL
statements
y Is persistent
y Facilitates workload capture/management
y Provides a common infrastructure for dealing
with SQL workloads
– Can be used as a source for different tuning tasks

25. SQL Tuning Advisor User
Interface
y GUI: Enterprise Manager
y Launch SQL Tuning Advisor from a SQL
Source page
– ADDM Finding page, or
– Top SQL page, or
– SQL Tuning Set (STS) page
y View/Implement SQL Tuning
Recommendations
y Command line: DBMS_SQLTUNE package

26. SQL Source: ADDM Finding

27. SQL Source: Top SQL

28. SQL Source: SQL Tuning Set

29. Enterprise Manager Interface
y Launch SQL Tuning Advisor from a SQL
Source page
– ADDM Finding page, or
– Top SQL page, or
– SQL Tuning Set (STS) page
y View/Implement SQL Tuning
Recommendations

30. SQL Tuning Recommendations — Overview

31. DBMS_SQLTUNE PL/SQL Package
y Contains API for SQL Tuning
– Create Tuning Task
– Execute Tuning Task
– Display Advisor
Recommendations
– Drop Tuning Task
– Create STS
– Populate STS
– Query STS Contents
– Drop STS
– Accept SQL Profile
– Drop SQL Profile
– Alter SQL Profile
Attribute
Tuning Task Management STS Management
SQL Profile Management

32. Automatic vs. Manual SQL Tuning
Manual Tuning
1. Get explain plan
2. Examine query objects and their sizes
3. Review and compare explain plan statistics with
execution statistics (stored in V$SQL view)
4. Identify the problem, e.g., “first rows” issue because
only recent data is ever displayed despite large history
being queried
5. Contact application vendor
6. Produce test case for vendor
7. Get a patch with appropriate code modifications from
the vendor
8. Install the patch in next maintenance cycle
Automatic Tuning
1. Run SQL Tuning
Advisor
2. Implement
recommendations.

33. SQL Access Advisor

34. SQL Access Advisor
Workload
Indexes Materialized Views
Materialized View Logs
SQL Access
Advisor

35. SQL Access Advisor Features
y De-mystifies access structure design for optimal
application performance
y Recommends indexes, materialized views, and
materialized view logs to create and/or drop for
faster performance
y Analyzes entire workload and not just independent
SQL statements
y Takes into account impact of new access
structures on DML operations
y Considers storage, creation and maintenance
costs

36. SQL Access Advisor Features
y Simultaneously considers
– index solutions
– materialized view solutions
– combinations of both
y Optimizes materialized views for
– maximum query rewrite usage
– fast refresh
y Recommends materialized view logs for fast refresh
y Combines similar indexes into single index
y Impact of new access structures on DML considered
y Considers storage, creation & maintenance costs

37. Usage Scenarios
Workload
User Defined
Hypothetical
Cursor Cache
Filter
Options
STS
SQL Access
Advisor

38. Filter Options
y Don’t have to use the entire workload
y Filter by
– Application or module name
– Number of SQL statements
– Queries during a specified time window
– Username
– Tables
y must be in this list
y not in this list

39. SQL Access Advisor User
Interface
y GUI: Enterprise Manager
– Launch SQL Access Advisor from Advisor Central
– Select workload source
– Set options
y Workload
y Recommendation
y Advanced
– Schedule job
– Review job and submit
– Monitor job
– View Recommendations
– Implement Recommendations
y Command line: DBMS_ADVISOR package

40. Launch SQL Access Advisor

41. Select Workload Source

42. Set Workload Options

43. Set Recommendation Options

44. Advanced Options

45. Advanced Tuning Options
y SQL statements will be tuned
according to the resources they use

46. Schedule Job

47. Review & Submit

48. Monitor the Job

49. View Recommendations

50. Implement Recommendations

51. Tips, Do’s, Dont’s

52. Capturing SQL Workload
y Use cursor cache capture capability of STS
– Run workload
– Capture workload in STS simultaneously
DBMS_SQLTUNE.CAPTURE_CURSOR_CACHE_SQLSET(
sqlset_name => ‘MY_STS’,
time_limit => 3600,
repeat_interval => 60,
sqlset_owner => own);

53. SQL Profile Cursor Sharing
y Cursor sharing can be enforced at database
or SQL level
– Database level: CURSOR_SHARING=FORCE
– SQL level: Set SQL Profile attribute
FORCE_MATCH=TRUE
DBMS_SQLTUNE.ACCEPT_SQL_PROFILE (
task_name => 'my_sql_tuning_task',
name => 'my_sql_profile',)
force_match => TRUE);

54. Tuning Considerations
y Resource consumption
– Running SQL advisors consumes CPU, I/O, memory and can
affect system performance
y Potential negative impact of recommendation
– Implementing recommendations may impact system
negatively, e.g., optimizer stats refresh
• Before initiating tuning, answer the following
questions
• How much resources will be consumed by tuning activity?
• Can the system spare resources needed for tuning?
• How can the production system be shielded from possible
negative impact of tuning actions?

55. Resource Consumption of SQL
Advisors
y SQL Tuning Advisor
– Limited mode: Resource consumption minimal
y Stats, index and SQL restructure analysis is cheap
y Average is less than 1 second per SQL statement
– Comprehensive mode: Resource consumption may be
significant
y SQL Profiling can potentially consume non-trivial resources
y Roughly comparable to amount of resources/time consumed
when executing SQL statement(s)
• SQL Access Advisor
• Resource consumption depends on size of SQL workload
• For small number of SQL, resource consumption not very high

56. Tuning Options
y Options
– Direct tuning of live system
– Remote tuning
y Live system tuning
– Run SQL Tuning Advisor in Comprehensive mode
– Run SQL Tuning Advisor in Limited mode only if …
y System does not have spare resources to tune SQL
– Run SQL Access Advisor for few SQL at a time
y Perform remote tuning, if …
– Cumulative resources/time consumed by all SQL
statements being tuned significant
– System cannot spare resources

57. Live System Tuning Tips
1. Ensure tables referenced in SQL have representative
optimizer stats
2. Run SQL Access Advisor
– For individual SQL, set “Recommendation Type” to indexes
– MV not suitable for tuning individual statements
3. Run SQL Tuning Advisor
– Test profile before making it PUBLIC
DBMS_SQLTUNE.ACCEPT_SQL_PROFILE (
task_name => ‘<tuning task name>’,
category => ‘MY_CATEGORY’);
ALTER SESSION SET SQLTUNE_CATEGORY=‘MY_CATEGORY’ ;
– Once satisfied with results set category to DEFAULT
DBMS_SQLTUNE.ALTER_SQL_PROFILE()

58. Remote Tuning Tips
1. Move SQL to Test
Production System Test System
2. Tune SQL
3. Apply recomm. on production
• Performed to shield production system from
performance impact of running SQL advisors

59. Remote Tuning Tips
y Move SQL to test
– Use Transportable STS
y DBMS_SQLTUNE.XXX_STGTAB_SQLSET
y Apply recommendation on production
– Use Transportable SQL Profiles
y DBMS_SQLTUNE.XXX_STGTAB_SQLPROF

60. Automatic SQL Tuning
Summary
SQL Access Advisor
Access Path: Materialized View Logs
SQL Access Advisor
Access Path: Materialized Views
SQL Tuning/Access
Advisor
Access Path: Indexes
SQL Tuning Advisor
SQL Structure
SQL Tuning Advisor
SQL Profile
SQL Tuning Advisor
Statistics
Performed By
Analysis Types
SQL Tuning Advisor and SQL Access Advisor
together completely automate SQL tuning

61. Conclusion
y SQL Advisors help address critical SQL tuning
challenges
y Provides targeted and automated tuning
y Makes possible comprehensive tuning of
packaged applications
y Eliminates need for highly skilled performance
experts

62. Thank You!

63. Q U E S T I O N S
Q U E S T I O N S
A N S W E R S
A N S W E R S