2008, 28 April CSCI585 - Distributed Databases

Distributed Databases

by Farnoush Banaei-Kashani

Excerpt from “Principles of Distributed Database Systems”by M. Tamer Özsu and Patrick Valduriez

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Topics

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Outline

� Problem Definition � Issues to Consider� Methodology

� Step 1: Query Decomposition� Step 2: Data Localization� Step 3: Global Optimization� Step 4: Local Optimization

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Query Processing

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Problem?

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Problem in DDBS?

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Problem in DDBS?

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Query Optimization Objectives

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Complexity of Relational Operations

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Outline

� Problem Definition � Issues to Consider� Methodology

� Step 1: Query Decomposition� Step 2: Data Localization� Step 3: Global Optimization� Step 4: Local Optimization

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Query Processing Issues – Types of Optimizers

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Query Processing Issues – Optimization Granularity

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Query Processing Issues – Optimization Timing

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Query Processing Issues – Statistics

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Query Processing Issues – Decision Sites

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Query Processing Issues – Network Topology

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Outline

� Problem Definition � Issues to Consider� Methodology

� Step 1: Query Decomposition� Step 2: Data Localization� Step 3: Global Optimization� Step 4: Local Optimization

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Distributed Query Processing Methodology

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Step 1 – Query Decomposition

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Normalization

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Analysis

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Analysis - Example

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Analysis - Example

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Simplification

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Simplification - Example

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Restructuring

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Restructuring - Transformation Rules

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Restructuring - Transformation Rules

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Example

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Equivalent Query

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Restructuring

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Distributed Query Processing Methodology

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Step 2 – Data Localization

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Example

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Provides Parallelism

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Eliminates Unnecessary Work

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Reduction for PHF

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Reduction for PHF

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Reduction for PHF

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Reduction for PHF

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Reduction for VF

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Reduction for DHF

≠

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Reduction for DHF

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Reduction for DHF

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Reduction for HF

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Reduction for HF