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distributed dbms
1. The document discusses distributed database management systems (DDBMS), which store and manage logically related data over physically independent sites connected by a network. 2. A DDBMS has several advantages over a centralized database like improved performance, reliability, and scalability but also greater complexity, security risks, and training costs. 3. The distribution of data and processing in a DDBMS can take different forms from single-site systems to fully distributed systems across multiple sites and servers. Transaction management and concurrency control are important challenges in distributed databases.
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distributed dbms
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- 2. Different Types ofDatabase System Contributed by: Isha Kushwah MCA-2008-11 Centralized database System 2
- 3. Content • What adistributed database management system (DDBMS) • DDBMS components • Database implementation is affected by different levels of data and process distribution • How transactions are managed in a distributed database environment • How database design is affected by the distributed database environment 3
- 4. Problem in Centralizeddatabase Management • Performance degradation • High cost • Reliability problems 5
- 5. DDBMS Advantages • Data located near site with greatest demand • Faster data access • Faster data processing • Growth facilitation • Improved communications • Reduced operating costs • User-friendly interface • Less danger of single-point failure • Processor independence 6
- 6. DDBMS Disadvantages • Complexity of management and control • Security • Lack of standards • Increased storage requirements • Greater difficulty in managing data environment • Increased training costs 7
- 7. Distributed Processing Shares database’slogical processing among physically, networked independent sites Figure 10.1 8
- 8. Distributed Database Stores logicallyrelated database over physically independent sites Figure 10.2 9
- 9. Distributed Database vs. Distributed Processing • Distributed processing – Does not require distributed database – May be based on a single database on single computer – Copies or parts of database processing functions must be distributed to all data storage sites • Distributed database – Requires distributed processing • Both – Require a network to connect components 10
- 10. Functions of DDBMS • Application/end user interface • Validation • Transformation • Query optimization • Mapping • I/O interface • Formatting • Security • Backup and recovery • DB Administration • Concurrency Control • Transaction Management 11
- 11. Centralized Database Figure 10.3 13
- 12. Fully Distributed Database Management System Figure 10.4 14
- 13. DDBMS Components • Computer workstations • Network hardware and software components • Communications media • Transaction processor (TP) – Also called application manager (AP) or transaction manager (TM) • Data processor (DP) – Also called data manager (DM) 15
- 14. Distributed Database Components Figure 10.5 16
- 15. DDBMS Protocols • Interfacewith network to transport data and commands between DPs and TPs • Synchronize data received from DPs and route to appropriate TPs • Ensure common database functions – Security – Concurrency control – Backup and recovery 17
- 16. Levels of Dataand Process Distribution Database systems can be classified based on process distribution and data distribution Table 10.1 18
- 17. Single-Site Processing, Single-Site Data (SPSD) • All processing on single CPU or host computer • All data are stored on host computer disk • DBMS located on the host computer • DBMS accessed by dumb terminals • Typical of mainframe and minicomputer DBMSs • Typical of 1st generation of single-user microcomputer database 19
- 18. Single-Site Processing, Single-Site Data (con’t.) Figure 10.6 20
- 19. Multiple-Site Processing, Single-Site Data (MPSD) • Requires network file server • Applications accessed through LAN • Variation known as client/server architecture Figure 10.7 21
- 20. Multiple-Site Processing, Multiple-Site Data (MPMD) • Fully distributed DDBMS with support for multiple DPs and TPs at multiple sites – Homogeneous I • Integrate one type of centralized DBMS over the network – Heterogeneous • Integrate different types of centralized DBMSs over a network 22
- 21. Heterogeneous Distributed Database Scenario Figure 10.8 23
- 22. Distributed DB Transparency •Allows end users to feel like only database user • Hides complexities of distributed database • Transparency features – Distribution – Transaction – Failure – Performance – Heterogeneity 24
- 23. Distribution Transparency • Allowsmanagement of a physically dispersed database as though it were centralized • Three Levels – Fragmentation transparency – Location transparency – Local mapping transparency Table 10.2 25
- 24. Transaction Transparency • Ensurestransactions maintain integrity and consistency • Completed only if all involved database sites complete their part of the transaction • Management mechanisms – Remote request – Remote transaction – Distributed transaction – Distributed request 26
- 25. Remote Request Figure 10.10 27
- 26. Remote Transaction Figure 10.11 28
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- 28. Distributed Requests Figure 10.13 30
- 29. Distributed Requests (con’t.) Figure 10.14 31
- 30. Distributed Concurrency Control •Multisite, multiple-process operations more likely to create data inconsistencies and deadlocked transactions • Problems – Transaction committed by local DP – One DP could not commit transaction’s result – Yields inconsistent database 32
- 31. Two-Phase Commit Protocol •DO-UNDO-REDO protocol – Write-ahead protocol – Two kinds of nodes • Coordinator • Subordinates • Phases – Preparation • Coordinator sends message to all subordinates • Confirms all are ready to commit or abort – Final Commit • Ensures all subordinates have committed or aborted 33
- 32. Performance Transparency and Query Optimization • Objective: Minimize total cost associated with execution of request • Main costs – Access time – Communication – CPU time • Basis for query optimization algorithms – Optimum execution order – Sites accessed to minimize communication costs • Automatic or Manual • Dynamic or static optimization • Statistically based vs. rule-based query optimization algorithms 34
- 33. Distributed Database Design •Partition database into fragments – Horizontal – Vertical – Mixed • Fragments to replicate – Storage of data copies at multiple sites – Fully, partially, unreplicated databases • Data allocation – Where to locate data – Centralized, partitioned, replicated 35
- 34. Client/Server Advantages OverDDBMS • Client/server less expensive • Client/server solutions allow use of microcomputer’s GUI • More people with PC skills than mainframe skills • PC is well established in workplace • Numerous data analysis and query tools exist • Considerable cost advantages to off-loading application development 36
- 35. Client/Server Disadvantages • Createsmore complex environment with different platforms • Increased number of users and sites creates security problems • Training issues become more complex and expensive 37
- 36. Date’s 12 Commandmentsfor Distributed Databases 1. Local Site Independence 2. Central Site Independence 3. Failure Independence 4. Location Transparency 5. Fragmentation Transparency 6. Replication Transparency 38
- 37. Date’s 12 Commandmentsfor Distributed Databases 7. Distributed Query Processing 8. Distributed Transaction Processing 9. Hardware Independence 10. Operating System Independence 11. Network Independence 12. Database Independence 39