Lecture Notes Unit3 chapter20 - Database System Architectures

RDBMS - Unit III
Chapter 20
Database System Architectures
Prepared By
Dr. S.Murugan, Associate Professor
Department of Computer Science,
AlagappaGovernment Arts College, Karaikudi.
(Affiliated by AlagappaUniversity)
Mailid: muruganjit@gmail.com
Reference Book:
Database System Concepts by Abraham Silberschatz, Henry
F.Korth , S. Sudharshan

Database System Architectures – Client Server Database System
➢ Networking of computers allows some tasks to be
executed on a server system and some tasks to be
executed on client systems.
➢ This division of work has led to client- server database
systems.

Database System Architectures – Parallel Processing System
➢ Parallel processing is a method of simultaneously
breaking up and running program tasks on multiple
microprocessors, thereby reducing processing time.
➢ Parallel processing may be accomplished via
a computer with two or more processors or via a
computer network.
➢ Parallel processing is also called parallel computing

Database System Architectures – Parallel Processing System

Database System Architectures – Distributed Data Processing System
➢ Distributed data processing is a computer-networking
method in which multiple computers across different
locations share computer-processing capability.

2O.1 CentraIized and Client - Server Architectures
➢ A modern, general-purpose computer system consists
of one to a few CPUs and a number of device
controllers that are connected through a common bus
that provides accessto shared memory as shown in
Figure 20.1.

2O.1 CentraIized and Client - Server Architectures
➢ A computer system may be single user or multi user.
➢ A typical single-user system is a desktop unit used by
a single person, usually with only one CPU and one or
two hard disks, and usually only one person using the
machine at a time.
➢ A typical multiuser system, on the other hand, has
more disks and more memory, may have multiple
CPUs and has a multiuser operating system.
➢ It serves a large number of users who are connected to
the system via terminals.

20.1.2 Client-Server Systems
➢ The centralized systems today act as server systems
that satisfy requests generated by client systems.
Figure 20.2 shows the general structure of a client-
server system.

20.1.2 Client-Server Systems
➢ The function of database can be broadly divided into
two parts. One is front-end and another one is Back-
end as shown in Figure 20.3.
➢ The front-end of a database system consists of tools
such as SQL user interface, forms interfaces, report
Generation.
➢ The back end manages access structures and query
Evaluation.
➢ The interface between the front end and the back end
is through SQL, or through an application program.

2O.2 Server System Architecture
➢ Server systems can be broadly categorized as
transaction servers and data servers.
➢ Transaction-server systems, also called query-
server which receives the answer from the server
based on the client request.
➢ Data-server systems allow clients to interact with the
servers by making requests to read or update data.

20.2.1 Transaction-Server Process Structure
➢ A transaction-server system consists of multiple
processes accessing data in shared memory, as in
Figure 20.4. The processes that form part of the
database system include.
➢ Server processes: These are processes that receive user
queries (transactions), execute them, and send the
results back to the client.
➢ Lock manager process: It includes lock grant, lock
release, and deadlock detection.

➢ Database writer process: The output can be stored
from spool into hard disk and user records.
➢ Log writer process: outputs log records from the log
record buffer to stable storage.
➢ Process monitor process: It takes recovery actions.

2O.2 Server System Architecture
➢ Data-server systems are used in local-area networks,
where there is a high-speed connection between the
clients and the server, the client machines are
comparable in processing power to the server
machine, and the tasks to be executed are computation
intensive.
➢ In such an environment, it makes sense to ship data to
client machines, to perform all processing at the client
machine (which may take a while), and then to ship
the data back to the server machine.
➢ Note that this architecture requires full back-end
functionality at the clients.
➢ Data-server architectures have been particularly
popular in object-oriented database systems.

2O.3 Parallel Systems
➢ Parallel systems improve processing and I/O speeds
by using multiple CPUs and disks in parallel.
➢ In parallel processing, many operations are performed
simultaneously, as opposed to serial processing, in
which the computational steps are performed
sequentially.
➢ A coarse-grain parallel machine consists of a small
number of powerful processors.
➢ A massively parallel or fine-grain parallel machine
uses thousands of smaller processors.

2O.3 Parallel Systems
There are two main measures of performance of a
database system:
(1) throughput, the number of tasks that can be
completed in a given time interval, and
(2) response time, the amount of time it takes to
complete a single task from the time it is submitted.

20.3.1 Speedup and Scaleup
➢ Two important issues in studying parallelism are
speedup and scaleup.
➢ Running a given task in less time by increasing the
degree of parallelism is called speedup.
➢ Handling larger tasks by increasing the degree of
parallelism is called scaleup.

20.3.2 lnterconnection Networks
➢ Parallel systems consist of a set of components
(processors, memory, and disks) that can communicate
with each other via an interconnection network
➢ Figure 20.7 shows three commonly used types of
interconnection networks:
(i) Bus
(ii) Mesh
(iii)Hybercube

20.3.2 lnterconnection Networks - Bus
➢ AII the system components can send data on and
receive data from a single communication bus. This
type of interconnection is shown in Figure (a).
➢ The bus could be an Ethernet or a parallel
interconnect.
➢ Bus architectures work well for small numbers of
processors.

20.3.2 lnterconnection Networks - Mesh
➢ The components are nodes in a grid, and each
component connects to all its adjacent components in
the grid.
➢ In a two-dimensional mesh each node connects to four
adjacent nodes, Figure (b) shows a two-dimensional
mesh.

20.3.2 lnterconnection Networks - Hybercube
➢ The components are numbered in binary, and a
component is connected to another if the binary
representations of their numbers differ in exactly one
bit.

20.3.3 Parallel Database Architectures
➢ There are several architectural models for parallel
machines.
➢ Among the most prominent ones are those in Figure
20.8 (in the figure, M denotes memory, P denotes a
processor, and disks are shown as cylinders):

➢ Shared memory. All the processors share a common
memory (Figure 20.8a).
➢ Shared disk. All the processors share a common set of
disks (Figure 20.8b). Shared-disk systems are
sometimes called clusters.
➢ Shared nothing. The processors share neither a
common memory nor common disk (Figure 20.8c).
➢ Hierarchical. This model is a hybrid of the preceding
three architectures (Figure 20.8d)

2O.4 Distributed Systems
➢ In a distributed database system, the database is stored
on several computers.
➢ The computers in a distributed system communicate
with one another through various communication
media, such as high-speed networks or telephone
lines. The general structure of a distributed system
appears in Figure 20.9.

S.No. Shared Nothing
Parallel DB
Distributed DB
1. Parallel databases are
not geographically
separated, not separately
administrated and have
a faster interconnection.
Distributed databases are
geographically separated, separately
administered, and have a slower
interconnection.
2. There is no difference in
local transaction and
global transaction.
There is a difference between local
transaction and global transaction. In
local transaction, accesses data only
from sites where the transaction was
initiated.
In global transaction, accesses data
in several different sites.

➢ Distributed systems are developed for the purpose of
sharing data, autonomy and availability.
➢ Sharing data: The user may able to access the data
from other site.
➢ Autonomy: Local database administrator is
available for every site.
➢ Availability: If one site fails in a distributed system,
the remaining sites may be able to continue
operating.

20.4.1 An Example of Distributed Database
➢ Consider a banking system consisting of four
branches in four different cities.
➢ Each branch has its own computer, with a database of
all the accounts maintained at that branch.
➢ There also exists one single site that maintains
information about all the branches of the bank.
➢ Each branch maintains a relation account
(Account_schema), where
Account_schema = (account_number, branch_name, ba
lance)

20.4.1 An Example of Distributed Database
➢ The site containing information about all the
branches of the bank maintains the reIation branch
(Branch_schema), where
Branch_schema= (branch_name, branch_city, assets)
➢ If the data were accessed from single site for the
transaction is called local transaction. For ex, fund
transfer from Account A to Account B in the same
branch with the same city.
➢ If the data were accessed from multiple site for the
transaction is called global transaction. For ex, fund
transfer from Account A to Account B in the same
branch with the different city.

20.4.2 lmplementation lssues
➢ Atomicity of transactions is an important issue in
building a distributed database system.
➢ If a transaction runs across two sites, it may commit
at one site and abort at another, leading to an
inconsistent state.
➢ This problem solved by the two-phase commit
protocol (2PC).
➢ The coordinator decides to commit the transaction
only if the transaction reaches the ready state at every
site where it executed; otherwise (for example, if the
transaction aborts at any site), the coordinator decides
to abort the transaction.

20.4.2 Implementation lssues
➢ Concurrency control is another issue in a distributed
database.
➢ Since a transaction may access data items at several
sites, transaction managers at several sites may need
to coordinate to implement concurrency control.
➢ If locking is used, locking can be performed locally
at the sites containing accessed data items, but there
is also a possibility of deadlock involving
transactions originating at multiple sites.
➢ Therefore deadlock detection needs to be carried out
across multiple sites.

20.4.2 Implementation lssues
➢ The primary disadvantage of distributed database
systems are:
➢ Software-development cost is high.
➢ Greater potential for bugs.
➢ Increased processing overhead.

2O.5 Network Types
➢ Distributed databases and client-server systems are
built around communication networks.
➢ There are basically two types of networks: local-area
networks and wide area networks.
S.No
.
Local Area Network Wide Area Network
1. processors are distributed
over small geographical
areas, such as a single
building or a number of
adjacent buildings.
a number of autonomous
processors are distributed over a
large geographical area (such as
the United States or the entire
world)

20.5.1 Local-Area Networks
➢ Local-area networks (LANs) (Figure 20.10) emerged
in the early 1970s as a way for computers to
communicate and to share data with one another.

➢ LANs are generally used in an office environment
➢ LANs have a higher speed and lower error rate than
WAN
➢ The most common links in a local-area network are
twisted pair, coaxial cable, fiber optics.
➢ Communication speeds range from a few megabits
per second to gigabits per second.

➢ A storage-area network (SAN) is a special type of
high-speed local-area network designed to connect
large banks of storage devices (disks) to computers
that use the data (see Figure 20.11).

20.5.2 Wide-Area Networks
➢ The first WAN to be designed and developed was the
Arpanet. Work on the Arpanet began in 1968.
➢ The Arpanet has grown from a four-site experimental
network to a worldwide network of networks, the
Internet comprising hundreds of millions of computer
systems.
➢ Data rates for wide-area links typically range from a
few megabits per second to hundreds of gigabits per
second.
➢ The last link, to end user sites, is often based on digital
subscriber line (DSL) technology or cable modem or
dial-up modem

20.5.2 Wide-Area Networks
➢ WANs can be classified into two types:
➢ In discontinuous connection WANs, such as those
based on wireless connections, hosts are connected to
the network only part of the time.
➢ In continuous connection WANs, such as the wired
Internet, hosts are connected to the network at all times.

Lecture Notes Unit3 chapter20 - Database System Architectures

More Related Content

Similar to Lecture Notes Unit3 chapter20 - Database System Architectures (20)

More from Murugan146644 (16)

Recently uploaded (20)

Lecture Notes Unit3 chapter20 - Database System Architectures