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Lamport’s Scalar Clocks

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Lamport’s Scalar Clocks

Shiva Bottu

Introduction

High level Implementation Details

Experimentation

Results

Further Research

Lamport’s logical clocks are introduced to capture causality relation in a distributed system.

Each process Pi has a logical clock Ci and for a particular event a in P, it assigns an integer value Ci, which is timestamp of the event.

Timestamps are monotonically increasing.

- There are 2 implementation rules that should be followed
- Before executing event, update timestamp value
Ci:=Ci+d

- When sending a message, attach the timestamp. When message is received by a process, timestamp of receive event is calculated as maximum of the two timestamps (timestamp of the process and timestamp received in the message)
Ci:=max(Ci,Cmsg)

- Number of processes are varied.
- Random flood algorithm is used to exchange messages between processes
- Part 1:
- Total number of updates are plotted against number of processes
- Average number of updates per process against number of processes

- Part 2:
- Number of updates and Number of messages against number of processes
- Number of processes against average number of messages required for each process

Number of clock updates

Number of Processes

Average clock updates

Number of Processes

clock updates & Messages

Number of Processes

No. of Messages per process

Number of Processes

From part-1(a), it is observed that the number of updates increase with increase in number of processes

From part-1(b), average number of updates per process increase with increase in number of processes

From part-2(a), we can observe that number of clock updates and number of messages increase with increase in no. of processes

From part-2(b), we can observe that average number of messages required per process increases with increase in number of processes

To change the base algorithm from random flood to other topologies and test with the same process.

Running with high load of processes.

http://en.wikipedia.org/wiki/Lamport_timestamps

http://cnlab.kaist.ac.kr/~ikjun/data/Course_work/CS642-Distributed_Systems/papers/lamport1978.pdf