Articles & Content


All About Query Optimization - Explaining the Impossible (Part 1 of 2) (C10)

Topic: DB2 for LUW

Subtopic: 2007

DATE: 2007-11-7 (13:30 - 14:30)
SPEAKERS: John Hornibrook (IBM Toronto Lab)

The query optimizer and the query execution plans (QEPs) it generates are key to the performance of the RDBMS. But query optimization is often a mysterious process and the choices made by the query optimizercan be difficult to understand. If you've ever wondered how an SQL statement gets optimized and how query executionplans are created, this presentation is for you. Using many QEP examples displayed with the Explain facility,this presentation will cover a variety of optimization topics including query rewrite and cardinality estimationand the cost model.

EXP. LEVEL: Intermediate


What is query optimization and why it is important

How queries are rewritten

How filtering, cardinalities and costs are computed

How access plans are chosen to optimize index access and different data organization schemes such as database and range partitioning and multidimensional clustering.

How to interpret Explain facility output

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