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Distributed Systems > chapter 1 > Flashcards

chapter 1 Flashcards

1
Q

what is a distributed system?

A

is a piece of software that ensures a collection of independent computers appear as a single coherent system to users.

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2
Q

what are the 2 aspects of a DS?

A
  • independent computers
  • middleware ; allows systems to communicate and manage data
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3
Q

what are the goals of a distributed system?

A
  • resource sharing
  • transparency
  • openness
  • scalability
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4
Q

what is relocation transparency?

A

DS hides possible object mov’t to a different location while in use

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5
Q

what is access transparency?

A

DS hides data representation & invocation mechanisms

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6
Q

list the types of distribution transparency.

A
  • access
  • location
  • relocation
  • migration
  • concurrency
  • replication - obj replication
  • failure
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7
Q

what do we mean by openness of a DS?

A

a systems ability to interact with services provided by a different system no matter the underlying environment.

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8
Q

what should a system do to be considered open?

A
  • conform to well defined interfaces
  • support application portability
  • easily interoperate
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9
Q

DS should be _______________ to achieve openness?

A

independent from heterogeneous underlying environments [ platform, hardware & languages ]

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10
Q

what policies need to be supported to implement openness?

A
  • level of consistency for client-cached data
  • level of secrecy during communication
  • QoS to follow when there’s a difference in bandwidth
  • operations allowed to be performed
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10
Q

what policies need to be supported to implement openness?

A
  • level of consistency for client-cached data
  • level of secrecy during communication
  • QoS to follow when there’s a difference in bandwidth
  • operations allowed to be performed
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11
Q

what is scalability

A

the ability to handle increased workload without adding new resources

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12
Q

what are the 3 components of scalability?

A
  • size scalability: number of users
  • geographic scalability: distance between nodes
  • administrative scalability: number of admin domains
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13
Q

what are the techniques for scaling?

A
  • hiding communication latencies
  • distribution
  • replication / caching
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14
Q

what scaling technique makes use of asynchronous communication?

A

hiding communication latencies

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15
Q

what is the problem when using hiding latencies scaling technique?

A

there are applications that can not make use of asynchronous communication

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16
Q

how does distribution, from scaling techniques work?

A

it splits data into smaller parts and spreads them across the system.

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17
Q

give examples of systems that use distribution techniques.

A
  • DNS: decentralized naming service
  • Java applets
  • WWW
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18
Q

how does replication / caching work?

A

by making copies of data available on different machines

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19
Q

give examples of caching & replication

A
  • web & file caching
  • mirrored websites & replicated servers
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20
Q

what scaling technique leads to inconsistencies?

A

caching / replication

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21
Q

what are the drawbacks of caching / replication?

A
  • multiple copies lead to inconsistencies
  • requires global synchronization
  • global synchronization makes large-scale solutions impossible
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22
Q

tolerating inconsistencies is application independent.

A

False

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23
Q

many distributed systems are needlessly complex.

A

True

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24
Q

what are the false assumptions associated with DSs.

A
  • reliable network
  • secure network
  • homogenous network
  • 0 latency
  • 0 transport cost
  • 1 admin
  • infinite bandwidth
  • unchanging topology
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25
Q

list types of DSs.

A
  • distributed pervasive system
  • distributed information system
  • distributed computing system

distribute PIC

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26
Q

many distributed systems are configured for ____________?

A

hight performance computing

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27
Q

what are the 2 subgroups of distributed computing systems?

A
  • cluster computing
  • grid computing
28
Q

explain cluster computing.

A

refers to a group of homogeneous computers [ hardware and OS ] connected through a LAN and each managed by a single node

29
Q

what is grid computing?

A

is a heterogeneous federation of computers where every computer may have a different hardware, software and network organization.

30
Q

which subgroup of computing DS can easily span a wide area network?

A

grid computing

31
Q

how does cluster computing handle tasks?

A

each node works on similar tasks, by dedicating to them as a single unit

32
Q

how does grid computing handle tasks?

A

each task is divided into independent subtasks which are assigned to d/t machines.

33
Q

what is cloud computing?

A

refers to storing and accessing data on remote servers hosted on the internet

33
Q

what is cloud computing?

A

refers to storing and accessing data on remote servers hosted on the internet

34
Q

what are the distinct layers in cloud computing?

A
  • hardware
  • application
  • platform
  • infrastructure
35
Q

what does the platform layer of cloud computing perform?

A

provides higher level abstraction for storage

36
Q

what does the hardware layer of cloud computing perform?

A

provides cooling systems, processors, routers …

37
Q

what does the application layer of cloud computing perform?

A

provides actual apps [ text processor, spreadsheet ]

38
Q

what does the infrastructure layer of cloud computing perform?

A

allocation and management of virtual storage

39
Q

the vast amount of distributed system in use today are originally ____________ ?

A

traditional info systems that now integrate legacy systems

39
Q

the vast amount of distributed system in use today are originally ____________ ?

A

traditional info systems that now integrate legacy systems

40
Q

what is an example of a distributed info system?

A

transaction processing system

41
Q

what operation does a transaction processing system perform?

A
  • begin_transaction
  • end_transaction
  • abort _ transaction
  • read
  • write
42
Q

which transaction operation tries to commit new values after terminating?

A

end_transaction

43
Q

which transaction operation tries to restore old values after terminating?

A

abort_transaction

44
Q

define a transaction.

A

a transaction is a collection of operations performed on an object that satisfies ACID properties.

45
Q

mebeten ACID.

A
  • atomicity
  • consistency
  • isolation
  • durability
46
Q

what do we mean by atomicity property?

A
  • all operations either succeed or fail. if a transaction fails, state of the object will be restored
46
Q

what do we mean by the consistency property?

A
  • invariants that held true before transaction, will hold true after. but may be violated in intermediate stages.
  • example - money in bank
46
Q

what do we mean by the isolation property?

A
  • concurrent transaction do not interfere with each other. they appear to run sequentially.
46
Q

what do we mean by the durability property?

A

after a transaction commits its effects are permanent.

46
Q

how is data in transaction handled?

A

distributed across servers as sub transaction with the Nested Transaction as a parent

46
Q

what is a ( transaction processing ) TP monitor?

A

is a program that manages the execution of a transaction from 1 stage to the next

46
Q

what is the problem with a TP monitor?

A
  • it doesn’t allow applications to communicate directly with each other since it doesn’t separate applications from their databases.
47
Q

how do applications exchange information in the case of TP monitors?

A
  • by means of request / reply behavior
48
Q

what is communication middleware?

A

is a software that allows inter application communication, there by overcoming the drawbacks of TP monitors.

49
Q

give examples of communication middleware.

A
  • remote procedure call
  • remote method invocation
  • message oriented middleware
50
Q

what is an RPC?

A
  • is an interprocess technique that allows applications to communicate with each other by doing local procedure calls.
51
Q

what is an RMI?

A
  • is basically the same as RPC but operates on objects instead of applications
52
Q

what is the drawback with RPC and RMI?

A
  • caller and callee both need to be running
  • caller and callee need to know hoe to refer to each other
53
Q

what is MOM?

A

provides mechanisms for applications to asynchronously exchange messages using message queue software

54
Q

what is a distributed pervasive system?

A

is the emerging next-generation of distributed systems characterized by being small, mobile, battery powered and embedded in larger systems.

55
Q

what are the requirements for a distributed pervasive system [ DPS ]?

A
  • contextual changes
  • ad hoc composition
  • default sharing
56
Q

what is meant by contextual change in DPS?

A
  • a device must be aware to changes in it’s environment.
  • eg : a network may be lost because user is moving, in this case the device should automatically connect to another network
57
Q

what is meant by Ad hoc composition in DPS?

A
  • d/t devices [ nodes ] in a pervasive system may be used d/tly by d/t users and hence REQUIRE ease of configuration.
58
Q

what is meant by default sharing in DPS?

A
  • nodes join a system to provide / access information, hence requires simple configuration
59
Q

give examples of a DPS?

A
  • home network [ pc, tv ]
  • personal electronics that monitor a person [ motion sensor watch ]

Distributed Systems (7 decks)

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