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Chapter 12 Distributed Data Bases Learning Objectives • What a distributed database management system (DDBMS) is and what its components are • How 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 Objectives of DDS B • Provide ease of access to users at different sites • Local autonomy • Create transparency • Faster response DDB A DB PHYSICALLY SPREAD ACROSS COMPUTERS AT MULTIPLE LOCATIONS CONNECTED BY A NETWORK AND IN WHICH USERS CAN ACCESS DATA AT ANY SITE IN THE NETWORK IS DEFINED AS DDB DISTRIBUTE DBMS A DBMS CAPABLE OF SUPPORTING AND MANIPULATING DDB • DETERMINE LOCATION OF REQUESTED DATA • TRANSFER REQUEST FROM ONE NODE TO ANOTHER NODE • RECOVERY, CONCURRENCY, DEADLOCK etc DDBMS a DDBMS is like a DBMS with additional responsibilities of communication and coordination of data storage and processing over several distributed sites Advantages of DDB • Data is located at the demand site faster data access • faster data processing • growth facilitation • better communication • reduced operating costs • user-friendly interface • less problem of a single point failure DDB disadvantages • • • • management & control security lack of standards storage problem A Fully Distributed Database Management System Distributed processing & distributed Databases • Distributed processing: Data is processed at multiple sites (Data maybe all in ONE location) DDB: Database is actually located on multiple sites (see fig 12.3) Skip pp462-463 Levels of processing Single site processing; single site data (see fig 12.6) Multiple site process; single site data (MPSD) All work is done (locking, selection etc. is done at user level) Multiple-site processing; multiple site data Figure D10.4 Multiple Requests and any Combination of Remote Databases REQUEST REQUEST REQUEST TRANSPARENCY: 1. DISTRIBUTION 1. FRAGMENTATION HIGHEST LEVEL DO NOT NEED TO SPECIFY FRAGMENT NAME OR LOCATION 2. LOCATION MUST SPECIFY NAME BUT not LOCATION 3. LOCAL Must specify both name and location of fragment Transparency Assuming part table is fragmented based on warehouse # Select * from Part Where warehouse =1; Select * from part1 Where warehouse=1; Select * from part1 node Chicago Where warehouse =1; Data fragmentation A process of splitting data in two or more fragments Horizontal Vertical mixed Using SQL type statements Begin: Define fragment fragment-name AS SQL statements End; Horizontal Fragmentation: (Based on warehouse) Ex: Begin: Define fragment PART1 AS Select * From PART Where warehouse=1 End; Vertical (based on say price) • Inventory department maybe interested in on hand inventory only but other may be interested in other attributes • Inventory..partnum,onhand,part desc • Production..partnum,class,warehouse,price Mixed Each item by warehouse number (horizontal) and then by inventory & production Transaction Transparency • Remote request (see 12.10) (single request) • Remote transaction (multiple requests) Distributed transaction (12.12/p472) (allows a transaction to reference several different locations Each single request can reference only one single site Distributed Request • Each transaction can request data from multiple sites Data Allocation: • data should be as close to the user as possible ISSUES IN DDB • • • • SOFTWARE COSTS & COMPLEXITY COORDINATION AMONG SITES DATA INTEGRITY SLOW RESPONSE • Q1/p487 Use the following summary: Number of DPs Operation 1 >1 Request Remot e Distribute d Transactio Remot Distribute