The Self-Managing Database: Guided Application and SQL Tuning

The Self-Managing Database:Guided Application and SQL Tuning

Mohamed ZiauddinConsulting Member of Technical Staff

Oracle Corporation

Session id: 40713

Agenda

SQL Tuning Challenges Automatic SQL Tuning Overview Usage Scenarios

– High load SQL tuning– Custom SQL workload tuning

User Interface– Enterprise Manager– DBMS_SQLTUNE PL/SQL package

Conclusion

Manual SQL Tuning Challenges

DBA

How can I

tune high-load

SQL?

High-LoadSQL

SQL

Workload

DBA

How can I

selecthigh-load

SQL?

Manual SQL Tuning Challenges

Requires expertise in several domains– SQL optimization: adjust the execution plan– Access design: provide fast data access– SQL design: use appropriate SQL constructs

Time consuming– Each SQL statement is unique– Potentially large number of statements to tune

Never ending task– SQL workload always evolving– Plan regressions

An Example Tuning Scenario

Manual Tuning

1. Get explain plan2. Examine query objects and their sizes3. Review and compare explain plan statistics with

execution statistics (stored in V$SQL view)4. Identify that it is a “first rows” issue because

only recent data is ever displayed despite large history being queried

5. Contact application vendor6. Produce test case for vendor7. Get a patch with “first rows” hint from the

vendor8. Install the patch in next maintenance cycle

Problem: Incorrect Optimizer Mode Selection

Intelligent Infrastructure

Application & SQLManagement

System ResourceManagement

SpaceManagement

Backup & RecoveryManagement

StorageManagement

Database Control

Database Management

Oracle 10g – SQL Tuning Solution

Oracle 10g Automates the SQL Tuning Process

I can do it for you !

SQL Tuning Advisor

DBAHigh-Load

SQL

ADDM

SQL

Workload

Agenda




Conclusion

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

RecommendationsSQL Tuning

Advisor

Automatic Tuning Optimizer (ATO)

It is the query optimizer running in tuning mode– Uses same plan generation process but performs

additional steps that require lot more time

It performs verification steps– To validate statistics and its own estimates

Uses dynamic sampling and partial executions to validate

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

Statistics Analysis

Add Missing Indexes






SQL Profiling

Statistics Analysis


DBA

SQL Tuning


Advisor

Statistics Analysis

Motivation– Statistics are key input to the query optimizer

Their availability and accuracy is very important

In Oracle10g, the Automatic statistics collection maintains statistics up to date…

– But it may not be enabled or properly configured!

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

SQL Profiling

Add Missing Indexes






SQL Profiling

Statistics Analysis


DBA

SQL Tuning


Advisor

SQL Profiling

Motivation– Empower the query optimizer to find a better plan

The query optimizer has time constraints– Makes compromises while finding right plan

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

SQL Profiling Flow

Optimizer(Tuning Mode)

createsubmit

SQL Profiling

Optimizer(Normal Mode)

outputsubmit

SQL Profile

SQL TuningAdvisor

DatabaseUsers

Well-Tuned

Plan

After …

use

SQL Profile It contains auxiliary information collected by the

ATO for a SQL statement– Customized optimizer settings

Based on past execution history (e.g., first_rows vs. all_rows)

– Compensation for missing or stale statistics– Compensation for errors in optimizer estimates

Estimation errors occur due to data skews and correlations, complex filters and joins

It doesn’t require any change to the SQL text– Ideal for Packaged Apps

It is persistent– Works across shutdowns and upgrades


Add Missing Indexes






SQL Profiling

Statistics Analysis


DBA

SQL Tuning


Advisor


Motivation– Adding an index may significantly improve the

performance of a SQL statement

Problem: A critical access path is missing– Index not created or mistakenly dropped

ATO explores the use of new indexes– Recommends an index if it provides a major

performance boost– Also recommends to run SQL Access Advisor to get

comprehensive index analysis based on a workload SQL Access Advisor also uses this analysis mode


Add Missing Indexes






SQL Profiling

Statistics Analysis


DBA

SQL Tuning


Advisor

SQL Structure Analysis Motivation

– Help application developers identify poorly written SQL statements

– Suggest restructuring of SQL for efficiency

Problem categories– Semantic changes of SQL operators (e.g., use

UNION ALL instead of UNION) Subject to user acceptance of new result

– Syntactic changes to predicates on indexed columns (e.g., remove type mismatch in column = :bind)

– Design issues (e.g., add missing join predicate to eliminate a large Cartesian join)

Agenda




Conclusion

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

SQL Tuning Set (STS)

Motivation– Enable user to tune a custom set of SQL statements

It is a new object in Oracle10g for capturing SQL workload

It stores SQL statements along with..– Execution context: parsing user, bind values, etc.– Execution statistics: buffer gets, CPU time, elapse

time, number of executions, etc.

It is created from a SQL source– Sources: AWR, cursor cache, user-defined SQL

workload, another STS

SQL Tuning Set Benefits

Allows selective, on-demand, custom SQL workload tuning

It simplifies tuning of a large number of SQL statements

It is persistent Provides a common infrastructure for dealing

with SQL workloads– Can be used as a source for different tuning tasks

Agenda




Conclusion

Enterprise Manager Interface

Launch SQL Tuning Advisor from a SQL Source page

– ADDM Finding page, or– Top SQL page, or– SQL Tuning Set (STS) page

View SQL Tuning Recommendations Implement SQL Tuning Recommendations

SQL Source: ADDM Finding

SQL Source: Top SQL

SQL Source: SQL Tuning Set

SQL Tuning Options

SQL Tuning Recommendations — Overview

SQL Tuning Recommendations — Details

Implement Recommendations

Agenda




Conclusion

DBMS_SQLTUNE PL/SQL Package

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

Conclusion

Manual Tuning

1. Get explain plan2. Examine query objects and their sizes3. Review and compare explain plan statistics

with execution statistics (stored in V$SQL view)

4. Identify that it is a “first rows” issue because only recent data is ever displayed despite large history being queried

5. Contact application vendor6. Produce test case for vendor7. Get a patch with “first rows” hint from the

vendor8. Install the patch in next maintenance cycle

Automatic Tuning

1. Run SQL Tuning Advisor

2. Implement SQL profile

Problem: Incorrect Optimizer Mode Selection

Recommended Sessions/Demos

Automatic SGA Memory Management (Tuesday, 5 PM, Room 103)

The Invisible Oracle: Deploying Oracle DB in Embedded Environments (Wednesday, 4:30 PM, Room 103

Automatic Health Monitoring (Thursday, 11:00 AM, Room 103

Proactive Performance Management

Automatic Memory Management

Proactive Space Management

Invisible Installation & Deployment

Automatic Storage Management

Easy Upgrade

Technical Sessions Campground Demos

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This was Session # 40173

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The Self-Managing Database: Guided Application and SQL Tuning

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