Distributed Database Management Systems: Lecture 4

Distributed Database Management Systems: Lecture 4. The main topics covered in this chapter include: fragmentation transparency; responsibility of transparency; performance improvement; through data localization; inter-query and intra-query parallelism; database design; query processing; concurrency control;...

Distributed Database  Management System 

Lecture 04

Fragmentation  Transparency

 Transparency is desirable but there 

is a compromise between level of  Transparency and difficulty/cost

 The language/Compiler:  to provide  uniform method of manipulating 

data. Avoid connectivity details. 

 Operating System : already 

provides in form of Device Drivers

 Can also provide network Trns. However  not all provide complete.

 Third layer is  DBMS  Uses features of 

Operating System in particular for 

network transparency.

 Practically, we get combination of all 

three.

DI NwT

Lan T R/F T

Layers of Transparency

 Reliability through Distributed 

Transactions: Avoids simple point of failure

 Concurrency Issues: Transaction involving  multiple records

 Failure Recovery: Involving multiple sites

Reliability in DDBS

 Through Data Localization

– Each site handles a portion of data, so 

contention of CPU or I/O is relatively less – Reduces remote access delays; no matter  how fast networks are latency delays are  there and may be unacceptable in certain  case

 Inter­query and Intra­query 

parallelism

 In case of Replication:

–Choose the appropriate copy

–Update impact reflected on all  replicas

 Failure Recovery

 Complexity

 Cost: hardware and also the 

duplication of manpower

 Distribution of Control may cause  problems if not used cautiously 

The Problem Areas

 Database Design

 Query Processing

 Concurrency Control

 OS Support

 Heterogeneity 

 Relationship among  them 

Directory Management

Distributed

DB Design

Concurrency Control

Deadlock Management

Reliability Query

Processing

Thanks