Introduction Dbms
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Outline ❏
Introduction ➠ What is a distributed DBMS ➠ Problems ➠ Current state-of-affairs
❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ Distributed DBMS
Background Distributed DBMS Architecture Distributed Database Design Semantic Data Control Distributed Query Processing Distributed Transaction Management Parallel Database Systems Distributed Object DBMS Database Interoperability Current Issues © 2001 M. Tamer Özsu & Patrick Valduriez
Page 1.1
File Systems
program 1 data description 1
File 1
program 2 data description 2
File 2
program 3 data description 3
Distributed DBMS
© 2001 M. Tamer Özsu & Patrick Valduriez
File 3
Page 1.2
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)
Distributed DBMS
© 2001 M. Tamer Özsu & Patrick Valduriez
Page 1.3
Motivation Database Technology
Computer Networks
integration
distribution
Distributed Database Systems integration integration ≠ centralization Distributed DBMS
© 2001 M. Tamer Özsu & Patrick Valduriez
Page 1.4
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.
Distributed DBMS
© 2001 M. Tamer Özsu & Patrick Valduriez
Page 1.5
Distributed Computing ■
Synonymous terms ➠ distributed function ➠ distributed data processing ➠ multiprocessors/multicomputers ➠ satellite processing ➠ backend processing ➠ dedicated/special purpose
computers ➠ timeshared systems ➠ functionally modular systems
Distributed DBMS
© 2001 M. Tamer Özsu & Patrick Valduriez
Page 1.6
What is distributed …
Distributed DBMS
■
Processing logic
■
Functions
■
Data
■
Control
© 2001 M. Tamer Özsu & Patrick Valduriez
Page 1.7
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 Distributed DBMS
© 2001 M. Tamer Özsu & Patrick Valduriez
Page 1.8
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
Distributed DBMS
© 2001 M. Tamer Özsu & Patrick Valduriez
Page 1.9
Centralized DBMS on a Network Site 1 Site 2 Site 5 Communication Network
Site 4
Distributed DBMS
Site 3
© 2001 M. Tamer Özsu & Patrick Valduriez
Page 1.10
Distributed DBMS Environment
Site 1 Site 2 Site 5 Communication Network
Site 4
Distributed DBMS
Site 3
© 2001 M. Tamer Özsu & Patrick Valduriez
Page 1.11
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
Distributed DBMS
© 2001 M. Tamer Özsu & Patrick Valduriez
Page 1.12
Shared-Memory Architecture
P1
Pn
M D
Examples : symmetric multiprocessors (Sequent, Encore) and some mainframes (IBM3090, Bull's DPS8) Distributed DBMS
© 2001 M. Tamer Özsu & Patrick Valduriez
Page 1.13
Shared-Disk Architecture
P1
Pn
M1
Mn
D
Examples : DEC's VAXcluster, IBM's IMS/VS Data Sharing
Distributed DBMS
© 2001 M. Tamer Özsu & Patrick Valduriez
Page 1.14
Shared-Nothing Architecture
P1 M1
D1
Pn
Dn
Mn
Examples : Teradata's DBC, Tandem, Intel's Paragon, NCR's 3600 and 3700 Distributed DBMS
© 2001 M. Tamer Özsu & Patrick Valduriez
Page 1.15
Applications ■ ■ ■ ■ ■ ■ ■
Distributed DBMS
Manufacturing - especially multi-plant manufacturing Military command and control EFT Corporate MIS Airlines Hotel chains Any organization which has a decentralized organization structure
© 2001 M. Tamer Özsu & Patrick Valduriez
Page 1.16
Distributed DBMS Promises ❶
Transparent management of distributed, fragmented, and replicated data
❷
Improved reliability/availability through distributed transactions
❸
Improved performance
❹
Easier and more economical system expansion
Distributed DBMS
© 2001 M. Tamer Özsu & Patrick Valduriez
Page 1.17
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 ◆ ◆ ◆
Distributed DBMS
horizontal fragmentation: selection vertical fragmentation: projection hybrid
© 2001 M. Tamer Özsu & Patrick Valduriez
Page 1.18
Example ASG
EMP ENO
ENAME
TITLE
E1 E2 E3 E4 E5 E6 E7 E8
J. Doe M. Smith A. Lee J. Miller B. Casey L. Chu R. Davis J. Jones
Elect. Eng. Syst. Anal. Mech. Eng. Programmer Syst. Anal. Elect. Eng. Mech. Eng. Syst. Anal.
ENO PNO
PROJ PNO
P1 P1 P2 P3 P4 P2 P2 P4 P3 P5 P3
Manager Analyst Analyst Consultant Engineer Programmer Manager Manager Engineer Engineer Manager
DUR 12 24 6 10 48 18 24 48 36 23 40
PAY PNAME
BUDGET
P1 Instrumentation 150000 P2 Database Develop. 135000 P3 CAD/CAM 250000 P4 Maintenance 310000 Distributed DBMS
E1 E2 E2 E3 E3 E4 E5 E6 E7 E7 E8
RESP
TITLE Elect. Eng. Syst. Anal. Mech. Eng. Programmer
© 2001 M. Tamer Özsu & Patrick Valduriez
SAL 40000 34000 27000 24000 Page 1.19
Transparent Access SELECT FROM WHERE AND AND
ENAME,SAL EMP,ASG,PAY DUR > 12 EMP.ENO = ASG.ENO 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
Montreal projects Paris projects Boston projects New York projects New York employees with budget > 200000 New York projects Montreal employees New York assignments Montreal assignments Distributed DBMS
© 2001 M. Tamer Özsu & Patrick Valduriez
Page 1.20
Distributed Database - User View
Distributed Database
Distributed DBMS
© 2001 M. Tamer Özsu & Patrick Valduriez
Page 1.21
Distributed DBMS - Reality DBMS Software
User Query User Application
DBMS Software
Communication Subsystem
DBMS Software
DBMS Software
User Query
DBMS Software
User Application
User Query Distributed DBMS
© 2001 M. Tamer Özsu & Patrick Valduriez
Page 1.22
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
Distributed DBMS
© 2001 M. Tamer Özsu & Patrick Valduriez
Page 1.23
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
Distributed DBMS
© 2001 M. Tamer Özsu & Patrick Valduriez
Page 1.24
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
Distributed DBMS
© 2001 M. Tamer Özsu & Patrick Valduriez
Page 1.25
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
Distributed DBMS
© 2001 M. Tamer Özsu & Patrick Valduriez
Page 1.26
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
Distributed DBMS
© 2001 M. Tamer Özsu & Patrick Valduriez
Page 1.27
Relationship Between Issues Directory Management
Query Processing
Distribution Design
Reliability
Concurrency Control Deadlock Management Distributed DBMS
© 2001 M. Tamer Özsu & Patrick Valduriez
Page 1.28
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
Distributed DBMS
© 2001 M. Tamer Özsu & Patrick Valduriez
Page 1.29
Introduction ➠ What is a distributed DBMS ➠ Problems ➠ Current state-of-affairs
❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ Distributed DBMS
Background Distributed DBMS Architecture Distributed Database Design Semantic Data Control Distributed Query Processing Distributed Transaction Management Parallel Database Systems Distributed Object DBMS Database Interoperability Current Issues © 2001 M. Tamer Özsu & Patrick Valduriez
Page 1.1
File Systems
program 1 data description 1
File 1
program 2 data description 2
File 2
program 3 data description 3
Distributed DBMS
© 2001 M. Tamer Özsu & Patrick Valduriez
File 3
Page 1.2
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)
Distributed DBMS
© 2001 M. Tamer Özsu & Patrick Valduriez
Page 1.3
Motivation Database Technology
Computer Networks
integration
distribution
Distributed Database Systems integration integration ≠ centralization Distributed DBMS
© 2001 M. Tamer Özsu & Patrick Valduriez
Page 1.4
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.
Distributed DBMS
© 2001 M. Tamer Özsu & Patrick Valduriez
Page 1.5
Distributed Computing ■
Synonymous terms ➠ distributed function ➠ distributed data processing ➠ multiprocessors/multicomputers ➠ satellite processing ➠ backend processing ➠ dedicated/special purpose
computers ➠ timeshared systems ➠ functionally modular systems
Distributed DBMS
© 2001 M. Tamer Özsu & Patrick Valduriez
Page 1.6
What is distributed …
Distributed DBMS
■
Processing logic
■
Functions
■
Data
■
Control
© 2001 M. Tamer Özsu & Patrick Valduriez
Page 1.7
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 Distributed DBMS
© 2001 M. Tamer Özsu & Patrick Valduriez
Page 1.8
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
Distributed DBMS
© 2001 M. Tamer Özsu & Patrick Valduriez
Page 1.9
Centralized DBMS on a Network Site 1 Site 2 Site 5 Communication Network
Site 4
Distributed DBMS
Site 3
© 2001 M. Tamer Özsu & Patrick Valduriez
Page 1.10
Distributed DBMS Environment
Site 1 Site 2 Site 5 Communication Network
Site 4
Distributed DBMS
Site 3
© 2001 M. Tamer Özsu & Patrick Valduriez
Page 1.11
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
Distributed DBMS
© 2001 M. Tamer Özsu & Patrick Valduriez
Page 1.12
Shared-Memory Architecture
P1
Pn
M D
Examples : symmetric multiprocessors (Sequent, Encore) and some mainframes (IBM3090, Bull's DPS8) Distributed DBMS
© 2001 M. Tamer Özsu & Patrick Valduriez
Page 1.13
Shared-Disk Architecture
P1
Pn
M1
Mn
D
Examples : DEC's VAXcluster, IBM's IMS/VS Data Sharing
Distributed DBMS
© 2001 M. Tamer Özsu & Patrick Valduriez
Page 1.14
Shared-Nothing Architecture
P1 M1
D1
Pn
Dn
Mn
Examples : Teradata's DBC, Tandem, Intel's Paragon, NCR's 3600 and 3700 Distributed DBMS
© 2001 M. Tamer Özsu & Patrick Valduriez
Page 1.15
Applications ■ ■ ■ ■ ■ ■ ■
Distributed DBMS
Manufacturing - especially multi-plant manufacturing Military command and control EFT Corporate MIS Airlines Hotel chains Any organization which has a decentralized organization structure
© 2001 M. Tamer Özsu & Patrick Valduriez
Page 1.16
Distributed DBMS Promises ❶
Transparent management of distributed, fragmented, and replicated data
❷
Improved reliability/availability through distributed transactions
❸
Improved performance
❹
Easier and more economical system expansion
Distributed DBMS
© 2001 M. Tamer Özsu & Patrick Valduriez
Page 1.17
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 ◆ ◆ ◆
Distributed DBMS
horizontal fragmentation: selection vertical fragmentation: projection hybrid
© 2001 M. Tamer Özsu & Patrick Valduriez
Page 1.18
Example ASG
EMP ENO
ENAME
TITLE
E1 E2 E3 E4 E5 E6 E7 E8
J. Doe M. Smith A. Lee J. Miller B. Casey L. Chu R. Davis J. Jones
Elect. Eng. Syst. Anal. Mech. Eng. Programmer Syst. Anal. Elect. Eng. Mech. Eng. Syst. Anal.
ENO PNO
PROJ PNO
P1 P1 P2 P3 P4 P2 P2 P4 P3 P5 P3
Manager Analyst Analyst Consultant Engineer Programmer Manager Manager Engineer Engineer Manager
DUR 12 24 6 10 48 18 24 48 36 23 40
PAY PNAME
BUDGET
P1 Instrumentation 150000 P2 Database Develop. 135000 P3 CAD/CAM 250000 P4 Maintenance 310000 Distributed DBMS
E1 E2 E2 E3 E3 E4 E5 E6 E7 E7 E8
RESP
TITLE Elect. Eng. Syst. Anal. Mech. Eng. Programmer
© 2001 M. Tamer Özsu & Patrick Valduriez
SAL 40000 34000 27000 24000 Page 1.19
Transparent Access SELECT FROM WHERE AND AND
ENAME,SAL EMP,ASG,PAY DUR > 12 EMP.ENO = ASG.ENO 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
Montreal projects Paris projects Boston projects New York projects New York employees with budget > 200000 New York projects Montreal employees New York assignments Montreal assignments Distributed DBMS
© 2001 M. Tamer Özsu & Patrick Valduriez
Page 1.20
Distributed Database - User View
Distributed Database
Distributed DBMS
© 2001 M. Tamer Özsu & Patrick Valduriez
Page 1.21
Distributed DBMS - Reality DBMS Software
User Query User Application
DBMS Software
Communication Subsystem
DBMS Software
DBMS Software
User Query
DBMS Software
User Application
User Query Distributed DBMS
© 2001 M. Tamer Özsu & Patrick Valduriez
Page 1.22
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
Distributed DBMS
© 2001 M. Tamer Özsu & Patrick Valduriez
Page 1.23
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
Distributed DBMS
© 2001 M. Tamer Özsu & Patrick Valduriez
Page 1.24
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
Distributed DBMS
© 2001 M. Tamer Özsu & Patrick Valduriez
Page 1.25
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
Distributed DBMS
© 2001 M. Tamer Özsu & Patrick Valduriez
Page 1.26
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
Distributed DBMS
© 2001 M. Tamer Özsu & Patrick Valduriez
Page 1.27
Relationship Between Issues Directory Management
Query Processing
Distribution Design
Reliability
Concurrency Control Deadlock Management Distributed DBMS
© 2001 M. Tamer Özsu & Patrick Valduriez
Page 1.28
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
Distributed DBMS
© 2001 M. Tamer Özsu & Patrick Valduriez
Page 1.29
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