UNIT-I. 11/14/00CSE 3802 UNIT-I Distributed Systems ECS-701 Lecture Note NEERAJ KUMAR.
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Transcript of UNIT-I. 11/14/00CSE 3802 UNIT-I Distributed Systems ECS-701 Lecture Note NEERAJ KUMAR.
UNIT-I
CSE 380 211/14/00
UNIT-IDistributed Systems
ECS-701Lecture Note
NEERAJ KUMAR
3
What is a Distributed System? Tanenbaum and van Renesse: A distributed system
is one that looks to its users like an ordinary, centralized, system but runs on multiple independent CPUs
Symptoms? Shroeder: Multiple, independent processing units Processors communicate via a hardware
interconnect Processing unit failures are independent Manage resource sharing State is shared among processors
Distributed Systems
4
Design Issues
Scaling Communication Coordination Transparency Naming Load sharing
Consistency Failures Security Heterogeneity Mobility
Distributed Systems, cont.
CSE 380 511/14/00
Advantages of Distributed Systems over Centralized Systems
• Economics: a collection of microprocessors offer a better price/performance than mainframes. Low price/performance ratio: cost effective way to increase computing power.
• Speed: a distributed system may have more total computing power than a mainframe. Ex. 10,000 CPU chips, each running at 50 MIPS. Not possible to build 500,000 MIPS single processor since it would require 0.002 nsec instruction cycle. Enhanced performance through load distributing.
• Inherent distribution: Some applications are inherently distributed. Ex. a supermarket chain.• Reliability: If one machine crashes, the system as a whole can still survive. Higher availability
and improved reliability.• Incremental growth: Computing power can be added in small increments. Modular
expandability• Another deriving force: the existence of large number of personal computers, the need for
people to collaborate and share information.
CSE 380 611/14/00
Advantages of Distributed Systems over Independent PCs
– Data sharing: allow many users to access to a common data base
– Resource Sharing: expensive peripherals like color printers– Communication: enhance human-to-human
communication, e.g., email, chat– Flexibility: spread the workload over the available
machines
CSE 380 711/14/00
Disadvantages of Distributed Systems
– Software: difficult to develop software for distributed systems
– Network: saturation, lossy transmissions– Security: easy access also applies to secrete data
Algorithms
• One processor– Reliable (no faults)– No communication
• Sequential: – One step at a time
• Complexity:– Step complexity
• Examples:– Sorting (Quicksort, Mergesort,
Heapsort)– Searching (Binary search)– Matrix mult. (Strassen’s)– Primality testing
Distributed kdAlgorithms Many processors
– Faulty (crash, byzantine, etc.)– Communication over network
Concurrent: – One step at a time
Complexity:– Message complexity– Latency analysis
Examples:– Leader election– Consensus (Agreement)– Mutual exclusion (Dining
Philosophers)– Atomic objects