Mumbai University > Computer Science > Sem 8 > Parallel And Distributed System

The concept of time in distributed systems is used to order events. The assumption is that the execution of a process is characterised by a sequence of events. An event can be the execution at one instruction or of one procedure or sending a message or receiving a message. Under some condition it is possible to ascertain the order of the events logical clocks try to catch this.

Logical clocks :

The happened before relation ( $\rightarrow$ ) is defined as follows :

$ A \rightarrow B$ if A & B are within the same process & A occured before B.

$ A \rightarrow B$ if A is an event at sending messages in one process end B is the event of receiving M in another process.

$ A \rightarrow B$ and $B \rightarrow C $ then $A \rightarrow C$

Event A causally affects event B if $A \rightarrow B$ distinct events A & B are ( A || B) if we do not have $A \rightarrow B$ or $ B \rightarrow A$

Example: