unit i adbms

8/10/2019 Unit I ADBMS

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Prepared by Prof Sujit K Singh

Unit I

ADBMS : CONCEPTS ANDARCHITECTURES


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UC Berkeley: IEOR 215

Centralized and Client-Server SystemsServer System ArchitecturesParallel Database

Distributed DatabaseWeb based system


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Centralized Systems Run on a single computer system and do not interact with other computer systems. General-purpose computer system: one to a few CPUs and a number of device

controllers that are connected through a common bus that provides access to sharedmemory.

Single-user system (e.g., personal computer or workstation): desk-top unit, singleuser, usually has only one CPU and one or two hard disks; the OS may support onlyone user.

Multi-user system: more disks, more memory, multiple CPUs, and a multi-user OS.Serve a large number of users who are connected to the system vie terminals. Oftencalled server systems.


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A Centralized Computer System


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Client-Server Systems Server systems satisfy requests generated at mclient systems, whose general structure is

shown below:


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Client-Server Systems (Cont.) Database functionality can be divided into:

Back-end: manages access structures, query evaluation and optimization,concurrency control and recovery.

Front-end: consists of tools such asforms, report-writers, and graphical userinterface facilities.

The interface between the front-end and the back-end is through SQL or through anapplication program interface.


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Client-Server Systems (Cont.) Advantages of replacing mainframes with networks of workstations or personalcomputers connected to back-end server machines:

better functionality for the cost

flexibility in locating resources and expanding facilities

better user interfaces easier maintenance


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Server System Architecture Server systems can be broadly categorized into two kinds: transaction serverswhich are widely used in relational database systems, and

data servers, used in object-oriented database systems


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Transaction Servers Also called query serversystems or SQLserversystems Clients send requests to the server

Transactions are executed at the server

Results are shipped back to the client.

Requests are specified in SQL, and communicated to the server through a remoteprocedure call (RPC) mechanism.

Transactional RPC allows many RPC calls to form a transaction.

Open Database Connectivity (ODBC) is a C language application program interfacestandard from Microsoft for connecting to a server, sending SQL requests, andreceiving results.

JDBC standard is similar to ODBC, for Java


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Transaction Server Process Structure

A typical transaction server consists of multiple processes accessing data in sharedmemory.

Server processes

These receive user queries (transactions), execute them and send results back

Processes may be multithreaded, allowing a single process to execute several userqueries concurrently

Typically multiple multithreaded server processes

Lock manager process

More on this later

Database writer process

Output modified buffer blocks to disks continually

Transaction Ser er Processes (Cont )


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Transaction Server Processes (Cont.)

Log writer process

Server processes simply add log records to log record buffer

Log writer process outputs log records to stable storage.

Checkpoint process

Performs periodic checkpoints

Process monitor process

Monitors other processes, and takes recovery actions if any of the other processes

fail E.g. aborting any transactions being executed by a server process and restarting

it

T ti S t P (C t )


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Transaction System Processes (Cont.)


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Transaction System Processes (Cont.)

Shared memory contains shared data Buffer pool

Lock table

Log buffer

Cached query plans (reused if same query submitted again)

All database processes can access shared memory

To ensure that no two processes are accessing the same data structure at the sametime, databases systems implement mutual exclusionusing either

Operating system semaphores

Atomic instructions such as test-and-set

To avoid overhead of interprocess communication for lock request/grant,each database process operates directly on the lock table

instead of sending requests to lock manager process Lock manager process still used for deadlock detection


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Data Servers Used in high-speed LANs, in cases where

The clients are comparable in processing power to the server

The tasks to be executed are compute intensive.

Data are shipped to clients where processing is performed, and then shipped resultsback to the server.

This architecture requires full back-end functionality at the clients.

Used in many object-oriented database systems

Issues:

Page-Shipping versus Item-Shipping

Locking

Data Caching

Lock Caching


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Data Servers (Cont.) Page-shippingversus item-shipping

Smaller unit of shippingmore messages

Worth prefetchingrelated items along with requested item

Page shipping can be thought of as a form of prefetching

Locking

Overhead of requesting and getting locks from server is high due to messagedelays

Can grant locks on requested and prefetched items; with page shipping,transaction is granted lock on whole page.

Locks on a prefetched item can be P{called back} by the server, and returned byclient transaction if the prefetched item has not been used.

Locks on the page can be deescalatedto locks on items in the page when thereare lock conflicts. Locks on unused items can then be returned to server.


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Data Servers (Cont.) Data Caching

Data can be cached at client even in between transactions

But check that data is up-to-date before it is used (cache coherency)

Check can be done when requesting lock on data item

Lock Caching

Locks can be retained by client system even in between transactions

Transactions can acquire cached locks locally, without contacting server

Server calls backlocks from clients when it receives conflicting lock request.Client returns lock once no local transaction is using it.

Similar to de-escalation , but across transactions.


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Cloud Computing?

The cloud is Internet-based computing,whereby shared resources, software, andinformation are provided to computersand other devices on demand pay peruse.

Cost-effective means of virtualising and making use ofresources more effectively Low start-up costs pay for use helps to kick-start companies

Scaling is proportional to demand (revenue) so it

s a good businessmodel

Vast range of Cloud Computing applications Virtual private servers, Web hosting, data servers, Transaction server,

etc


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Basic Cloud Characteristics The no-need-to-knowin terms of the underlying details

of infrastructure, applications interface with the

infrastructure via the APIs.

The flexibility and elasticityallows these systems to

scale up and down at will

utilising the resources of all kinds

CPU, storage, server capacity, load balancing, and databases

The pay as much as used and neededtype of utility

computing and the always on, anywhere and any place

type of network-based computing.

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Basic Cloud Characteristics Cloud are transparent to users and applications, they can be

built in multiple ways

branded products, proprietary open source, hardware or

software.

In general, they are built on clusters of PC servers plus Open

Source software combined with in-house applications and/orsystem software.

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Motivation Example: Forbes.com

You offer on-line real timestock market data

Why pay for capacityweekends, overnight?

9 AM - 5 PM,M-F

ALL OTHER

TIMES

Rate of

Server

Accesses


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Forbes' Solution

Host the web site inAmazon's EC2 Elastic ComputeCloud

Provision new servers every day, and deprovisionthem every night

Pay just $0.10* per server per hour

* more for higher capacity servers

Let Amazon worry about the hardware!


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virtualization to the next step

You dont have to own the hardware

You rentit as needed from a cloud

There are public clouds

e.g. Amazon EC2, and now many others (Microsoft, IBM,Sun, and others ...)

A company can create a private one

With more control over security, etc.

Cl d C ti O i


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Cloud Computing Overview


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A Basic Introduction


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Web Based system :Web servers are the machines or programs from which requests are

made and fulfilled over the Internet. They provide one of theendpoints in communication when users request an online service

Tiermean a physical tier defined by a physical server.

Layermean a section of the system that is contained within its own process or

deployment unit. Multiple layers may co exist on one tier.

Business LogicA workflow or procedure that defines the way a company conducts business .


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Client Server Architecture

A network architecturein which each computeror process on thenetwork is either aclientor a server.

May 2002 UNT Center for Digital Knowledge 27

Source: http://webopedia.lycos.com


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Components Clients

Servers

Communication Networks


Client

Server


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Clients Applications that run on computers

Rely on servers for

Files

Devices

Processing power Example: E-mail client

An application that enables you to send and receive e-mail


Clients are Applications


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Servers Computers or processes that manage network resources

Disk drives (file servers)

Printers (print servers)

Network traffic (network servers) Example: Database Server

A computer system that processes database queries


Servers Manage Resources

Cli S C i


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ClientServer Computing

Process takes place

on the server and on the client

Servers

Store and protect data

Process requests from clients Clients

Make requests

Format data on the desktop


Client-Server Computing Optimizes

Computing Resources


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Problem Of Client/Server The biggest and the most pressing problem at that time was one

of connection count

Servers were often licensed per client connection

In the 1990's most databases began to become heavily and thespeed of database reduced


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3-Tier Architecture Come To Solve Client/Server Problems

A middle layer can solve these problems(Transactionprocessing monitors, Message servers, Application servers,Object Request Brokers (ORB))


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N-Tier Architecture


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N Tier Architecture N-Tier: An unlimited number of tiers.

Each tier may have multiple computers.

Advantages: More powerful applications

Many services to many clients

Enhanced security, scalability and availability

Disadvantages: Much more complicated to design and model

Performance risks

Reliability is more difficult to achieve

More difficult to maintain software


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Types Of N-Tier Architecture

Business Logic


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Business Logic

Business logicis a non-technical term generally used todescribe the functional algorithms that handleinformation exchange between a database and a userinterface.

models real life business objects (such as accounts, loans,itineraries, and inventories)

enforces the methods by which business objects are accessedand updated.

business rules that express business policy (such as Taxes,logistics, prices, and products)


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Location of business logic

In a multilayered architecture (2-tire architecture)business logic is a separate module.

In the common 3-tier architecture, the business logic is

the middle tier.


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Business Logic SOAP (Simple Object Access Protocol) SOAP is an XML-based messaging protocol. It defines a set of

rules for structuring messages that can be used for simple one-way messaging but is particularly useful for performing RPC-style (Remote Procedure Call) request-response dialogues.

It is not tied to any particular transport protocol though HTTP ispopular. Nor is it tied to any particular operating system orprogramming language so theoretically the clients and servers inthese dialogues can be running on any platform and written inany language as long as they can formulate and understandSOAP messages


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SOAP (Simple Object Access Protocol) is a way for aprogram running in one kind of operating system (such as

Windows 2000) to communicate with a program in thesame or another kind of an operating system (such asLinux) by using the World Wide Web's HypertextTransfer Protocol (HTTP)and its Extensible MarkupLanguage (XML) as the mechanisms for informationexchange .

SOAP was developed byMicrosoft, DevelopMentor, andUserland Software and has been proposed as a standardinterface to the Internet Engineering Task Force (IETF).

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