Logic Clock

SLIDES CREATED BY SHRIDEEP PALLICKARA L34.5 CSx55 Distributed Systems Dept. Of Computer Science, Colorado State University C LOGICAL CLOCKS OMPUTER SCIENCE DEPARTMENT Professor SHRIDEEP PALLICKARA L34.9 Lamport's logical clocks The happens-before relation a and b are events in the process and a occurs before b Then a b is true a is event of message sent by one process

Figure 2, Lamport Clock. Let, Ca the counter value logical time when a happened. Cb the counter value logical time when b happened. So, If a happens before b a b in the

According to Happened before relation, we can come out an event order algorithm to use logic clock rather than physical logic. Our goal is de ne a notion of time value CA of event A, CB is the time notion of event B, If A !B then CA lt CB. If A and B are concurrent, then CA lt or gt CB. Lamport developed an logic clock algorithm to

time, we propose a hybrid logical clock, HLC, that com-bines the best of logical clocks and physical clocks. HLC captures the causality relationship like logical clocks, and enables easy identication of consistent snapshots in dis-tributed systems. Dually, HLC can be used in lieu of phys-icalNTP clocks since it maintains its logical clock to be

Lamport's Logical Clock was created by Leslie Lamport. It is a procedure to determine the order of events occurring. It provides a basis for the more advanced Vector Clock Algorithm. Due to the absence of a Global Clock in a Distributed Operating System Lamport Logical Clock is needed. Algorithm

Lamport's Logical Clocks The algorithm of Lamport timestamps is a simple algorithm used to determine the order of events in a distributed computer system. As different nodes or processes will typically not be perfectly synchronized, this algorithm is used to provide a partial ordering of events with minimal overhead, and conceptually provide a

clocks, and a bound is derived on how far out of synchrony the clocks can become. Key Words and Phrases distributed systems, computer networks, clock synchronization, multiprocess systems CR Categories 4.32, 5.29 Introduction The concept of time is fundamental to our way of thinking.

The logic clock's stability how long it takes to measure the time is 1.210 15 for a 1-second measurement, which is near the best achieved by a single ion clock but about 10 times worse than both NIST lattice clocks. The quantum logic clock got its nickname because it borrows logical decision-making techniques from experimental quantum

A logical clock is a mechanism for capturing chronological and causal relationships in a distributed system.Often, distributed systems may have no physically synchronous global clock. In many applications such as distributed GNU make, if two processes never interact, the lack of synchronization is unobservable and in these applications it is enough for the processes to agree on the event

3 Logical Clocks n For many problems, internal consistency of clocks is important n Absolute time is less important n Use logical clocks n Key idea n Clock synchronization need not be absolute n If two machines do not interact, no need to synchronize them n More importantly, processes need to agree on the order in which events occur rather than the time at which they occurred