'Unclustered index 1 nkeys' diaporamas de présentation

Lecture #7

Lecture #7. Query Optimization May 16 th , 2002. Agenda/Administration. Exam date set: June 10 th , 6:30pm. Place TBA. Volunteers for presenting projects during last class. Project demos. Schedules coming soon. Query Optimization. Major issues: Transformations (we saw a few, more coming)

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Query Optimization

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Instructor: Chen Li

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Overview of Query Optimization

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Relational Query Optimization

Relational Query Optimization. Query Processing: Topic 2. Overview of Query Optimization. Plan : Tree of R.A. ops, with choice of alg for each op.

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Relational Query Optimization

Relational Query Optimization. Query Processing: Topic 2. Overview of Query Optimization. Plan : Tree of R.A. ops, with choice of alg for each op.

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Relational Query Optimization

Relational Query Optimization. Chapter 15. Highlights of System R Optimizer. Impact: Most widely used currently; works well for < 10 joins. Cost estimation: Approximate art at best. Statistics, maintained in system catalogs, used to estimate cost of operations and result sizes.

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Relational Query Optimization

Relational Query Optimization. Chapters 14. Query Blocks: Units of Optimization. SELECT S.sname FROM Sailors S WHERE S.age IN ( SELECT MAX (S2.age) FROM Sailors S2 GROUP BY S2.rating ).

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Query Rewrite: Predicate Pushdown (through grouping)

Query Rewrite: Predicate Pushdown (through grouping). Select bid, Max(age) From Reserves R, Sailors S Where R.sid=S.sid GroupBy bid Having Max(age) > 40. Select bid, Max(age) From Reserves R, Sailors S Where R.sid=S.sid and S.age > 40 GroupBy bid.

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Relational Query Optimization

Relational Query Optimization. Module 5, Lecture 2. Overview of Query Optimization. Plan : Tree of R.A. ops, with choice of alg for each op.

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Cost Estimation

Cost Estimation. For each plan considered, must estimate cost: Must estimate cost of each operation in plan tree. Depends on input cardinalities. Must estimate size of result for each operation in tree! Use information about the input relations.

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