1. Massively Distributed Database Systems - Distributed DBS Spring 2014 Ki-Joune Li http://isel.cs.pusan.ac.kr/~lik Pusan National University

2. Pros and Cons Reliability and Availability Local Control Incremental Growth Communication Costs Fast Response Advantages Reliability and Availability Local Control Incremental Growth Communication Costs Fast Response Advantages Software Cost and Complexity Processing Overhead Data Integrity Slow Response Disadvantages Software Cost and Complexity Processing Overhead Data Integrity Slow Response Disadvantages

3. 3-layer model of databases External Layer Conceptual Layer Physical LayerData Storage Format Conceptual Schema View Definitions Implementation - Systems Modeling

4. Local Database Distributed Databases as a Logical Layers External Layer Conceptual Layer Physical Layer External Layer Conceptual Layer Physical Layer External Layer Conceptual Layer Physical Layer Global Conceptual Layer Local Database Global Physical Layer Global Database View from client ??

5. Issues Replication vs. Partitioning Distributed DBMS Transparency Query Optimization Transaction Management

6. Replication vs. Partitioning Replication Partitioning Vertical vs. Horizontal Hybrid

7. Replicate all or parts of databases to local DB Site 1 Replication DB-1 DB-2 DB-3 Site 2 DB-1 DB-2 Site 2 DB-2 DB-3

8. How to manage replicated DBs? Issue 1 – Consistency If updates at a site, how to manage the integrity of global databases Issue 2 – How to duplicate All or only some parts Factors to consider

9. Replication – Management of Consistency Snapshot replication Store all update logs at a central site from a given time Periodically send proper logs to local sites Each local site reflects the update logs for its local DB Near Real-Time replication When an update occurs, it triggers updates at other sites Pull Replication Instead of push protocol, each local site asks update logs when it is necessary

10. Replication – Management of Consistency Exclusive ownership vs. Shared ownership Single update vs. Multiple update Synchronous updates vs. Asynchronous update Simple snapshot vs. Multiple snapshot

11. Replication – How to replicate Fast Response Communication Overhead Security Query Optimization

12. Partitioning – Horizontal Partitioning Split a table into several subtables

13. Partitioning – Horizontal Partitioning How to split a table? Efficiency Local Optimization Communication Overhead Security Dynamic reconfiguration of Partitioning

14. Partitioning – Vertical Partitioning Split a DB into several disjoint tables  Shared Primary Keys – Join operations are inevitable

15. Comparison btw Replication and Partitions

16. Distributed DBMS What a distributed DBMS should do ⁻Management of Data Dictionary ⁻Resolving Heterogeneity: Schema, QL, DBMS ⁻Keeping distributed DBs secure and consistent: TM ⁻Transparency: single logical view to user ⁻Dynamic load balancing ⁻Query processing (Optimization)