1. Distributed Databases Midterm review

2. Lectures covered Everything until (including) March 2 nd Everything until (including) March 2 nd Focus on distributed databases integrity Focus on distributed databases integrity No specific security coverage (except DB Security overview, January 26 and chapter 5.2) No specific security coverage (except DB Security overview, January 26 and chapter 5.2) Farkas2

3. Reading materials All lecture notes All lecture notes Textbook chapters Textbook chapters –Chapter 1 Introduction (1.1-1.6) –Chapter 2 Background (2.1) –Chapter 3 Distributed Database Design (All understand main concepts, 3.3 and 3.4 read only) –Chapter 4 (All understand main concepts) Farkas3

4. Reading materials Textbook Textbook –Chapter 5 Access control (5.2) –Chapter 10 Transaction management (10.1-10.2) –Chapter 11 concurrency control (All, focus on 2PL) –Chapter 12 Reliability (All, focus on 2PC) –Chapter 13 Replication (13.1 – 3) Farkas4

5. 5 Database Management System (DBMS) Collection of Collection of –interrelated data and –set of programs to access the data Convenient and efficient processing of data Convenient and efficient processing of data Database Application Software Database Application Software

6. Farkas6 Abstraction View level: different perspectives View level: different perspectives –application programs hide irrelevant data Logical level: data models Logical level: data models –Logical representation of data –Different approaches: relational, hierarchical, network, object oriented, semi-structured, etc. – Data independence principle Physical level: how data is stored Physical level: how data is stored

7. Motivation for DBMS Integrate related data Integrate related data Provide centralized and controlled access to data Provide centralized and controlled access to data Farkas7

8. Computer Network Distributed processing: Distributed processing: –Number of autonomous processing elements that are interconnected by computer network –Cooperate to perform their assigned tasks Farkas8

9. What to distribute? Processing logic/element Processing logic/element Functions Functions Data Data Control of execution Control of execution Farkas9

10. Why to distribute? Intuition Intuition Reliability Reliability Performance Performance Farkas10

11. Distributed Database Systems Distributed database: Distributed database: –Collection of multiple, logically interrelated databases that are distributed over a computer network Distributed DBMS: software system that Distributed DBMS: software system that –Permits the management of the distributed database and –Makes the distribution transparent to the user Farkas11

12. Data Delivery Data storage and query processing Data storage and query processing Data delivery: Data delivery: –Delivery mode: push, pull, hybrid –Frequency: periodic, conditional, ad-hoc, irregular –Communication method: unicast, one-to-many Farkas12

13. DDBMS Services Transparent data management Transparent data management –Distributed, replicated data –Transparency: network, replica, fragmentation Reliable access to data Reliable access to data –Distributed transactions –Failure atomicity Improved performance Improved performance Flexible expansion Flexible expansion Farkas13

14. Difficulties Everything that is present in traditional DBs Everything that is present in traditional DBs Replica control Replica control –Data retrieval –Data update Dealing with failures Dealing with failures Synchronization Synchronization Farkas14

15. DDBMS Issues Database design Database design Directory management Directory management Query processing Query processing Concurrency control Concurrency control Deadlock management Deadlock management Reliability Reliability Replication Replication Farkas15

16. Summary cont. –Chapter 11: Concurrency control 2PL, lock types, deadlock management (no specifics about TO alg.) 2PL, lock types, deadlock management (no specifics about TO alg.) –Chapter 12: reliability 2PC, site and communication failures, window of uncertainty 2PC, site and communication failures, window of uncertainty –Chapter 13: replicated databases Goals, issues, types of replica control alg., advantages, disadvantages Goals, issues, types of replica control alg., advantages, disadvantages Farkas16

17. Farkas17 Next Class Access Control Current research issues