Clocks

Logical Clocks Sunetri P. Dasari Summer 2005 CSC8980 Distributed Systems Instructor: Sushil K. Prasad

What are Logical Clocks ? ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Lamport’s Contribution (1/2) ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Lamport’s Contribution (2/2) ,[object Object],[object Object],[object Object],[object Object]

Happens Before Relation “->” ,[object Object],[object Object],[object Object],[object Object]

Logical Clocks (2/2) ,[object Object]

Three processes, each with its own clock. The clocks run at different rates.

Lamport's algorithm corrects the clocks.

Total Ordering with Logical Clocks

Totally-Ordered Multicasting ,[object Object]

Scalar Logical Time: Pros and Cons ,[object Object],[object Object],[object Object],[object Object],[object Object]

What are Vector Timestamps ? ,[object Object],[object Object],[object Object],[object Object]

What are Vector Timestamps ? ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Illustration of Vector timestamps [1,0,0,0] [2,0,0,0] [0,0,1,0] [2,1,1,0] p 0 p 1 p 2 p 3 [0,0,0,1] [2,2,1,0] [2,1,1,1] [1,0,0,0] [1,0,1,0] [2,0,1,0] [2,2,1,1] [2,2,1,0]

Vector timestamps accurately represent happens-before relation ,[object Object],[object Object],[object Object],[object Object],[object Object]

Vector Clock Consistency ,[object Object],[object Object],[object Object],[object Object],[object Object]

Matrix Time ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Matrix Time Protocol ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Matrix Clock Consistency ,[object Object],[object Object],[object Object],[object Object],[object Object]

Ordered Message Delivery: Issues ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

End-to-end Argument ,[object Object],[object Object],[object Object]

References ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Clocks

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