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1
DB09 (^) Introduction
Prepared by Ling Liu
CS 4420 Database System Implementation
Query Processing
and Query Optimization
Ling Liu Associate Professor College of Computing, Georgia Tech
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DB09 (^) Introduction
Prepared by Ling Liu
Lecture Outline
Review of Last Lecture: z Summary of Multi-dimensional Indexing Techniques
z Query Processing (Part I) Æ Query Processing Steps Æ Algebraic Transformation & Logical Query Plans
Today’s Lecture
z Query Processing (cont) ÆAlgebraic Based Optimization ) Good transformations ÆCost-based Query Optimization )Intermediate Result Estimation )I/O Blocks Estimation
3
DB09 (^) Introduction
Prepared by Ling Liu
Query Processing Phases
Relational algebra level
z Algebraic transformations z good transformations
Detailed query plan level
z estimate costs (intermediate results size, I/O blocks) z generate and compare plans
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DB09 (^) Introduction
Prepared by Ling Liu
Relational Query Optimization
Relational algebra level
z Using Heuristics for good transformations to reduce the search space of local query plans z Typical Heuristics Æ Push Selection and Projection closer to the base relations in a SQL query tree. Æ Reduce intermediate result size as much as possible
Physical (Executable) query plan level
z Consider various indexes and their performance characteristics when estimating costs of alternative query plans z Pick the most economical physical query plan for query execution
