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Chapter 17

Chapter 17. Client-Server Processing, Parallel Database Processing, and Distributed Databases. Outline. Overview Client-Server Database Architectures Parallel Database Architectures Architectures for Distributed Database Management Systems Transparency for Distributed Database Processing

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Chapter 17

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  1. Chapter 17 Client-Server Processing, Parallel Database Processing, and Distributed Databases

  2. Outline • Overview • Client-Server Database Architectures • Parallel Database Architectures • Architectures for Distributed Database Management Systems • Transparency for Distributed Database Processing • Distributed Database Processing

  3. Evolution of Distributed Processing and Distributed Data • Need to share resources across a network • Timesharing (1970s) • Remote procedure calls (1980s) • Client-server computing (1990s)

  4. Timesharing Network

  5. Simple Resource Sharing

  6. Client-Server Processing

  7. Distributed processing and data

  8. Motivation for Client-Server Processing • Flexibility: the ease of maintaining and adapting a system • Scalability: the ability to support scalable growth of hardware and software capacity • Interoperability: open standards that allow two or more systems to exchange and use software and data

  9. Motivation for Parallel Database Processing • Scaleup: increased work that can be accomplished • Speedup: decrease in time to complete a task • Availability: increased accessibility of system • Highly available: little downtime • Fault-tolerant: no downtime

  10. Motivation for Distributed Data • Data control: locate data to match an organization’s structure • Communication costs: locate data close to data usage to lower communication cost and improve performance • Reliability: increase data availability by replicating data at more than one site

  11. Summary of Distributed Processing and Data

  12. Client-Server Database Architectures • Client-Server Architecture is an arrangement of components (clients and servers) among computers connected by a network. • A client-server architecture supports efficient processing of messages (requests for service) between clients and servers.

  13. Design Issues • Division of processing: the allocation of tasks to clients and servers. • Process management: interoperability among clients and servers and efficiently processing messages between clients and servers. • Middleware: software for process management

  14. Tasks to Distribute • Presentation: code to maintain the graphical user interface • Validation: code to ensure the consistency of the database and user inputs • Business logic: code to perform business functions • Workflow: code to ensure completion of business processes • Data access: code to extract data to answer queries and modify a database

  15. Middleware • A software component that performs process management. • Allow clients and servers to exist on different platforms. • Allows servers to efficiently process messages from a large number of clients. • Often located on a dedicated computer.

  16. Client-Server Computing with Middleware

  17. Types of Middleware • Transaction-processing monitors: relieve the operating system of managing database processes • Message-oriented middleware: maintain a queue of messages • Object-request brokers: provide a high level of interoperability and message intelligence • Data access middleware: provide a uniform interface to relational and non relational data using SQL

  18. Two-Tier Architecture

  19. Two-Tier Architecture • A PC client and a database server interact directly to request and transfer data. • The PC client contains the user interface code. • The server contains the data access logic. • The PC client and the server share the validation and business logic.

  20. Three-Tier Architecture (Middleware Server)

  21. Three-Tier Architecture (Application Server)

  22. Three-Tier Architecture • To improve performance, the three-tier architecture adds another server layer either by a middleware server or an application server. • The additional server software can reside on a separate computer. • Alternatively, the additional server software can be distributed between the database server and PC clients.

  23. Multiple-Tier Architecture • A client-server architecture with more than three layers: a PC client, a backend database server, an intervening middleware server, and application servers. • Provides more flexibility on division of processing • The application servers perform business logic and manage specialized kinds of data such as images.

  24. Multiple-Tier Architecture

  25. Multiple-Tier Architecture with Web Server

  26. Web Service Architecture • Generalize multiple-tier architectures for electronic business commerce • Supports services provided/used by automated agents • Advantages • Deploy services faster • Communicate services in standard formats • Find services easier

  27. Web Service Components

  28. Web Service Standards • HTTP, FTP, TCP-IP • Simple Object Access Protocol: XML message sending • Web Service Description Language (WSDL) • Universal Description, Discovery Integration • Web Services Flow Language

  29. Parallel DBMS • Uses a collection of resources (processors, disks, and memory) to perform work in parallel • Divide work among resources to achieve desired performance (scaleup and speedup) and availability. • Uses high speed network, operating system, and storage system • Purchase decision involves more than parallel DBMS

  30. Basic Architectures

  31. Clustering Architectures

  32. Design Issues • Load balancing: CN architecture most sensitive • Cache coherence: CD architecture problem • Interprocessor communication: CN architecture most sensitive • Application transparency: no knowledge about parallelism

  33. Oracle Real Application Clusters

  34. Oracle RAC Features • Cache fusion to synchronize cache access • Query optimizer intelligence • Connection load balancing • Automatic failover • Comprehensive administration interface

  35. IBM DB2 SPF

  36. IBM SPF Features • Automatic or DBA determined partitioning • Query optimizer intelligence • High scalability • Partitioned log parallelism

  37. Distributed Database Architectures • DBMSs need fundamental extensions. • Underlying the extensions are a different component architecture and a different schema architecture. • Component Architecture manages distributed database requests. • Schema Architecture provides additional layers of data description.

  38. Global Requests

  39. Component Architecture

  40. Schema Architecture I

  41. Schema Architecture II

  42. Distributed Database Transparency • Transparency is related to data independence. • With transparency, users can write queries with no knowledge of the distribution, and distribution changes will not cause changes to existing queries and transactions. • Without transparency, users must reference some distribution details in queries and distribution changes can lead to changes in existing queries.

  43. Motivating Example

  44. Fragments Based on the CustRegion Column

  45. Fragments Based on the WareHouseNo Column

  46. Fragmentation Transparency • Fragmentation transparency provides the highest level of data independence. • Users formulate queries and transactions without knowledge of fragments (locations, or local formats). • If fragments change, queries and transactions are not affected.

  47. Location Transparency • Location transparency provides a lesser level of data independence than fragmentation transparency. • Users need to reference fragments in formulating queries and transactions. • However, knowledge of locations and local formats is not necessary.

  48. Local Mapping Transparency • Local mapping transparency provides a lesser level of data independence than location transparency. • Users need to reference fragments at sites in formulating queries and transactions. • However, knowledge of local formats is not necessary.

  49. Oracle Distributed Databases • Homogeneous and heterogeneous distributed databases • Emphasis on site autonomy • Provides local mapping transparency • Each site is a separately managed database.

  50. Oracle Links • One way link from local to remote • Support remote access to other users’ objects • Necessary to have knowledge of remote database objects • Use synonyms and views with links to reduce remote database knowledge

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