CS 212 Distributed Database Systems Introduction to Distributed

CS- 212 Distributed Database Systems Introduction to Distributed Database Systems Ms. Mariam Nosheen Computer Science Department, LCWU, Lhr 1

Course Outline Introduction • What is a distributed DBMS • Problems • Current state-of-affairs Background Distributed DBMS Architecture Distributed Database Design Data Access Control Distributed Query Processing Distributed Transaction Management Consistency of Replicated Databases Current Issues Ms. Mariam Nosheen CS- 212 Distributed Database Systems 2

Introduction to Distributed Database Systems File Systems program 1 File 1 data description 1 program 2 File 2 data description 2 program 3 File 3 data description 3 Ms. Mariam Nosheen CS- 212 Distributed Database Systems 3

Introduction to Distributed Database Systems Database Management Application program 1 (with data semantics) Application program 2 (with data semantics) DBMS description manipulation control database Application program 3 (with data semantics) Ms. Mariam Nosheen CS- 212 Distributed Database Systems 4

Introduction to Distributed Database Systems Motivation Database Technology Computer Networks integration distribution Distributed Database Systems integration ≠ centralization Ms. Mariam Nosheen CS- 212 Distributed Database Systems 5

Introduction to Distributed Database Systems Distributed Computing • A concept in search of a definition and a name. • A number of autonomous processing elements (not necessarily homogeneous) that are interconnected by a computer network and that cooperate in performing their assigned tasks. Ms. Mariam Nosheen CS- 212 Distributed Database Systems 6

Introduction to Distributed Database Systems Distributed Computing • Synonymous terms • • Ms. Mariam Nosheen distributed function distributed data processing multiprocessors/multicomputers satellite processing backend processing dedicated/special purpose computers timeshared systems functionally modular systems CS- 212 Distributed Database Systems 7

Introduction to Distributed Database Systems What is distributed … • Processing logic • Functions • Data • Control Ms. Mariam Nosheen CS- 212 Distributed Database Systems 8

Introduction to Distributed Database Systems What is a Distributed Database System? A distributed database (DDB) is a collection of multiple, logically interrelated databases distributed over a computer network. A distributed database management system (D–DBMS) is the software that manages the DDB and provides an access mechanism that makes this distribution transparent to the users. Distributed database system (DDBS) = DDB + D–DBMS Ms. Mariam Nosheen CS- 212 Distributed Database Systems 9

Introduction to Distributed Database Systems What is not a DDBS? • A timesharing computer system • A loosely or tightly coupled multiprocessor system • A database system which resides at one of the nodes of a network of computers - this is a centralized database on a network node Ms. Mariam Nosheen CS- 212 Distributed Database Systems 10

Introduction to Distributed Database Systems Centralized DBMS on a Network Site 1 Site 2 Site 5 Communication Network Site 4 Ms. Mariam Nosheen Site 3 CS- 212 Distributed Database Systems 11

Introduction to Distributed Database Systems Distributed DBMS Environment Site 1 Site 2 Site 5 Communication Network Site 4 Ms. Mariam Nosheen Site 3 CS- 212 Distributed Database Systems 12

Introduction to Distributed Database Systems Implicit Assumptions • Data stored at a number of sites each site logically consists of a single processor. • Processors at different sites are interconnected by a computer network no multiprocessors • parallel database systems • Distributed database is a database, not a collection of files data logically related as exhibited in the users’ access patterns • relational data model • D-DBMS is a full-fledged DBMS • not remote file system, not a TP system Ms. Mariam Nosheen CS- 212 Distributed Database Systems 13

Introduction to Distributed Database Systems Shared-Memory Architecture P 1 Pn M D Examples : Ms. Mariam Nosheen symmetric multiprocessors (Sequent, Encore) and some mainframes (IBM 3090, Bull's DPS 8) CS- 212 Distributed Database Systems 14

Introduction to Distributed Database Systems Shared-Disk Architecture P 1 Pn M 1 Mn Examples : Ms. Mariam Nosheen D DEC's VAXcluster, IBM's IMS/VS Data Sharing CS- 212 Distributed Database Systems 15

Introduction to Distributed Database Systems Shared-Nothing Architecture P 1 Pn D 1 M 1 Examples : Ms. Mariam Nosheen Dn Mn Teradata's DBC, Tandem, Intel's Paragon, NCR's 3600 and 3700 CS- 212 Distributed Database Systems 16

Introduction to Distributed Database Systems Applications • Manufacturing - especially multi-plant manufacturing • Military command control • EFT • Corporate MIS • Airlines • Hotel chains • Any organization which has a decentralized organization structure Ms. Mariam Nosheen CS- 212 Distributed Database Systems 17

Introduction to Distributed Database Systems Advantages of Distributed DBMS Ms. Mariam Nosheen CS- 212 Distributed Database Systems 18

Introduction to Distributed Database Systems Advantages of Distributed DBMS Ms. Mariam Nosheen CS- 212 Distributed Database Systems 19

Introduction to Distributed Database Systems Advantages of Distributed DBMS Ms. Mariam Nosheen CS- 212 Distributed Database Systems 20

Introduction to Distributed Database Systems Advantages of Distributed DBMS Ms. Mariam Nosheen CS- 212 Distributed Database Systems 21

Introduction to Distributed Database Systems Distributed DBMS Promises Transparent management of distributed, fragmented, and replicated data Improved reliability/availability through distributed transactions Improved performance Easier and more economical system expansion Ms. Mariam Nosheen CS- 212 Distributed Database Systems 22

Introduction to Distributed Database Systems Transparency • Transparency is the separation of the higher level semantics of a system from the lower level implementation issues. • Fundamental issue is to provide data independence in the distributed environment • Network (distribution) transparency • Replication transparency • Fragmentation transparency • horizontal fragmentation: selection • vertical fragmentation: projection • hybrid Ms. Mariam Nosheen CS- 212 Distributed Database Systems 23

Introduction to Distributed Database Systems Data Independence Ms. Mariam Nosheen CS- 212 Distributed Database Systems 24

Introduction to Distributed Database Systems Network Transparency Ms. Mariam Nosheen CS- 212 Distributed Database Systems 25

Introduction to Distributed Database Systems Replication Transparency Ms. Mariam Nosheen CS- 212 Distributed Database Systems 26

Introduction to Distributed Database Systems Fragmentation Transparency Ms. Mariam Nosheen CS- 212 Distributed Database Systems 27

Introduction to Distributed Database Systems Why should provide Transparency? Ms. Mariam Nosheen CS- 212 Distributed Database Systems 28

Introduction to Distributed Database Systems Example ASG EMP ENO ENAME TITLE ENO RESP DUR E 1 P 1 Manager 12 E 2 P 1 Analyst 24 E 1 J. Doe Elect. Eng. E 2 M. Smith Syst. Anal. E 3 A. Lee Mech. Eng. E 2 P 2 Analyst E 4 J. Miller Programmer E 3 P 3 Consultant 10 E 5 B. Casey Syst. Anal. E 3 P 4 Engineer 48 E 6 L. Chu Elect. Eng. E 4 P 2 Programmer 18 E 7 R. Davis Mech. Eng. E 5 P 2 Manager 24 E 8 J. Jones Syst. Anal. E 6 P 4 Manager 48 E 7 P 3 Engineer 36 E 7 P 5 Engineer 23 E 8 P 3 Manager 40 PROJ PNO Ms. Mariam Nosheen PNO 6 PAY PNAME BUDGET TITLE SAL P 1 Instrumentation 150000 Elect. Eng. 40000 P 2 Database Develop. 135000 Syst. Anal. 34000 P 3 CAD/CAM 250000 Mech. Eng. 27000 P 4 Maintenance 310000 Programmer 24000 CS- 212 Distributed Database Systems 29

Introduction to Distributed Database Systems Transparent Access SELECT ENAME, SAL FROM EMP, ASG, PAY WHERE DUR > 12 AND EMP. ENO = ASG. ENO AND PAY. TITLE = EMP. TITLE Tokyo Paris Boston Communication Network Paris projects Paris employees Paris assignments Boston employees Boston projects Boston employees Boston assignments Montreal New York Boston projects New York employees New York projects New York assignments Ms. Mariam Nosheen CS- 212 Distributed Database Systems Montreal projects Paris projects New York projects with budget > 200000 Montreal employees Montreal assignments 30

Introduction to Distributed Database Systems Distributed Database - User View Distributed Database Ms. Mariam Nosheen CS- 212 Distributed Database Systems 31

Introduction to Distributed Database Systems Distributed DBMS - Reality DBMS Software User Query User Application DBMS Software Communication Subsystem User Query DBMS Software User Application User Query Ms. Mariam Nosheen CS- 212 Distributed Database Systems 32

Introduction to Distributed Database Systems Potentially Improved Performance • Proximity of data to its points of use • Requires some support for fragmentation and replication • Parallelism in execution • Inter-query parallelism • Intra-query parallelism Ms. Mariam Nosheen CS- 212 Distributed Database Systems 33

Introduction to Distributed Database Systems Parallelism Requirements • Have as much of the data required by each application at the site where the application executes • Full replication • How about updates? • Updates to replicated data requires implementation of distributed concurrency control and commit protocols Ms. Mariam Nosheen CS- 212 Distributed Database Systems 34

Introduction to Distributed Database Systems System Expansion • Issue is database scaling • Emergence of microprocessor and workstation technologies • Demise of Grosh's law • Client-server model of computing • Data communication cost vs telecommunication cost Ms. Mariam Nosheen CS- 212 Distributed Database Systems 35

Introduction to Distributed Database Systems Distributed DBMS Issues • Distributed Database Design • how to distribute the database • replicated & non-replicated database distribution • a related problem in directory management • Query Processing • convert user transactions to data manipulation instructions • optimization problem • min{cost = data transmission + local processing} • general formulation is NP-hard Ms. Mariam Nosheen CS- 212 Distributed Database Systems 36

Introduction to Distributed Database Systems Distributed DBMS Issues • Concurrency Control • synchronization of concurrent accesses • consistency and isolation of transactions' effects • deadlock management • Reliability • how to make the system resilient to failures • atomicity and durability Ms. Mariam Nosheen CS- 212 Distributed Database Systems 37

Introduction to Distributed Database Systems Relationship Between Issues Ms. Mariam Nosheen CS- 212 Distributed Database Systems 38

Introduction to Distributed Database Systems Related Issues • Operating System Support • operating system with proper support for database operations • dichotomy between general purpose processing requirements and database processing requirements • Open Systems and Interoperability • Distributed Multidatabase Systems • More probable scenario • Parallel issues Ms. Mariam Nosheen CS- 212 Distributed Database Systems 39