Distributed Processing, Client/Server, and Clusters

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Distributed Processing, Client/Server, and
Clusters

• Source Prentice-Hall Web Site

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Client/Server Computing

• Client machines are generally single-user PCs or
  workstations that provide a highly user-friendly
  interface to the end user
• Each server provides a set of shared user
  services to the clients
• The server enables many clients to share access
  to the same database and enables the use of a
  high-performance computer system to manage the
  database

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Client/Server Computing

• Involves splitting an application into tasks and
  putting each task on the platform where it can be
  handled most efficiently
• Processing for the presentation on the users
  machine
• Data management and storage on a server
• Involves a network

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Generic Client/Server Environment
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Client/Server Applications

• Platforms and the operating systems of client and
  server may differ
• These lower-level differences are irrelevant as
  long as a client and server share the same
  communications protocols and support the same
  applications

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Client/Server Applications

• Actual functions performed by the application can
  be split up between client and server
• Optimize platform and network resources
• Optimize the ability of users to perform various
  tasks
• Optimize the ability to cooperate with one
  another using shared resources

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Database Applications

• The server is a database server
• Interaction between client and server is in the
  form of transactions
• the client makes a database request and receives
  a database response
• Server is responsible for maintaining the database

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Client/Server Architecture for Database
Applications
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Classes of Client/Server Applications

• Host-based processing
• not true client/server computing
• traditional mainframe environment

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Classes of Client/Server Applications

• Server-based processing
• server does all the processing
• user workstation provides a user-friendly
  interface

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Classes of Client/Server Applications

• Client-based processing
• all application processing may be done at the
  client
• data validation routines and other database logic
  function are done at the server

Server
Client
Presentation Logic
Application Logic
Database Logic
Database Logic
DBMS
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Classes of Client/Server Applications

• Cooperative processing
• application processing is performed in an
  optimized fashion
• complex to set up and maintain

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File Cache Consistency

• File caches hold recently accessed file records
• Caches are consistent when they contain exact
  copies for remote data
• File-locking prevents simultaneous access to a
  file
• writing causes the server cached to be updated

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Middleware

• Set of tools that provide a uniform means and
  style of access to system resources across all
  platforms
• Enable programmers to build applications that
  look and feel the same
• Enable programmers to use the same method to
  access data

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Middleware

• Use of a standard programming interface and
  protocols
• There is both a client and server component to
  middleware
• Provides uniform access to different systems

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The Role of Middleware in Client/Server
Architecture
Client Workstation
Server
Middleware
Middleware Interaction
Communications Software
Application Services
Protocol Interaction
Server Operating System
Hardware Platform
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Logical View of Middleware
APIs
Platform Interfaces
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Distributed Message Passing

• Message passed used to communicate among
  processes
• Send and receive messages as used in a single
  system OR
• Remote procedure calls

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Basic Message-Passing Primitives
ProcessID
Message
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Message-oriented Middleware
Client
Server
Message-oriented Middleware
Message-oriented Middleware
Application
Application
Transport
Transport
Network
Network
Application-specific messages
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Remote Procedure Calls

• Allow programs on different machines to interact
  using simple procedure call/return semantics
• Widely accepted
• Standardized
• client and server modules can be moved among
  computers and operating systems easily

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Remote Procedure Call Mechanism
Client Application
Remote Server Application
Local Response
Local Response
Local Procedure Call
Local Response
Local Procedure Calls
Local Application or Operating System
Local Stub
Local Stub
Remote Procedure Call
RPC Mechanism
RPC Mechanism
Remote Procedure Call
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Client/Server Binding

• Binding specifies the relationship between remote
  procedure and calling program
• Nonpersistent binding
• logical connection established during remote
  procedure call
• Persistent binding
• connection is sustained after the procedure
  returns

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Remote Procedure Calls
Client
Server
Application
Application
Transport
Transport
Network
Network
Application-specific Procedure Invocations and
Returns
RPC Stub Program
RPC Stub Program
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Object Request Broker
Client
Server
Object Request Broker
Application
Object Server
Transport
Transport
Network
Network
Transport
RPC Stub Program
Network
Object Requests and Responses
Object Requests and Responses
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Clusters

• Alternative to symmetric multiprocessing (SMP)
• Group of interconnected, whole computers working
  together as a unified computing resource
• illusion is one machine
• system can run on its own

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Clusters

• Separate server
• each computer is a separate server
• no shared disks
• need management or scheduling software
• data must be constantly copied among systems so
  each is current

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Clusters
Standby Server with No Shared Disk
P
P
P
P
High-Speed Message Link
M
M
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Clusters

• Shared nothing
• reduces communication overhead
• servers connected to common disks
• disks partitioned into volumes
• each volume owned by a computer
• if computer fails another computer gets ownership
  of the volume

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Clusters
Shared Disk
High-Speed Message Link
P
P
P
P
M
M
RAID
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Clusters

• Shared disk
• multiple computers share the same disks at the
  same time
• each computer has access to all of the volumes on
  all of the disks

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Win2000 Cluster Server

• Formerly called Wolfpack
• Shared-nothing cluster
• Concepts
• Cluster Service Software that manages
  cluster-specific activity
• Resource Item to be managed
• Physical Disk drives, Network cards
• Logical Volumes, TCP/IP addresses, Applications,
  Databases
• Online A resource is online at a node when it
  is providing service on that node
• Group A collection of resources managed as a
  unit
• Helps manage resources, load balancing
• Usually a set of resources needed for a specific
  application

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Win2000 Cluster Server
Components Node Manager Maintain membership
Uses heartbeat messages to track system Database
Manager Maintain cluster configuration database
(resources, groups, ownership) Uses
fault-tolerant transaction software Resource
Manager Make decisions concerning resources,
startup, failover Event Processor Connect
components
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Beowulf

• From NASA High Performance Computing and
  Communications Project, based on commodity
  hardware
• Implemented as an add-on to Linux, and each node
  runs a copy of Linux, with kernel extensions for
  global namespaces
• Examples of Beowulf system software
• Beowulf Distributed Process Space Allow process
  ID space to span machines, provide single system
  image, start processes on other nodes
• Beowulf Ethernet Channel Bonding Combine
  multiple low-cost links into a single logical
  network
• Pvmsync Provide synchronization and shared data
  objects in a cluster
• EnFuzion Set of tools for parametric computing