What are logical clocks How are they different from physical clocks?
A logical clock is a mechanism for capturing chronological and causal relationships in a distributed system. Distributed systems may have no physically synchronous global clock, so a logical clock allows global ordering on events from different processes in such systems.
What are different types of clock in distributed system?
There are 2 types of clock synchronization algorithms: Centralized and Distributed. Centralized is the one in which a time server is used as a reference. The single time server propagates its time to the nodes and all the nodes adjust the time accordingly.
What is Lamport logical clock in distributed system?
A Lamport logical clock is a numerical software counter value maintained in each process. Conceptually, this logical clock can be thought of as a clock that only has meaning in relation to messages moving between processes. When a process receives a message, it re-synchronizes its logical clock with that sender.
What is physical clock and logical clock?
Most of the physical clocks are based on cyclic processes such as a celestial rotation. … A physically synchronous global clock may not be present in a distributed system. In such systems a logical clock allows global ordering on events from different processes.
What is the use of logical clock?
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.
What is the physical clock?
A physical clock is a physical process coupled with a method of measuring that process to record the passage of time. … Most physical clocks are based on cyclic processes (such as a celestial rotation). One or more physical clocks are used to establish a time-line clock for a temporal database.
Why is synchronization necessary?
Clock synchronization is necessary for the ordering of events and to preserve the state of resources. As per algorithms, we can say that for clock synchronization there is need to consider propagation time of messages among each node in both types of algorithms centralized and distributed.
In which system synchronization is difficult?
Communication between processes in a distributed system can have unpredictable delays, processes can fail, messages may be lost ▪ Synchronization in distributed systems is harder than in centralized systems because the need for distributed algorithms.
What is the advantage of a vector clock over Lamport logical clock?
Vector Clocks represent an extension of Lamport Timestamps in that they guarantee the strong clock consistency condition which (additionally to the clock consistency condition) dictates that if one event’s clock comes before another’s, then that event comes before the other, i.e., it is a two-way condition.
What does happens before relation mean in Lamport logical clocks?
To synchronize logical clocks Lamport defined a relation called happens-before. The Happen-Before relation can be observed directly in two situations. 1) If A & B are events in same process and A occurs before B, then A B is true. … The Happen-Before is a transitive relation, so if AB & BC then AC.