distributed fault recovery

Please read slides on fault recovery alogrithm prepared by Prof. Gagan first.

Claim: Orphan messages are not acceptable by this algorihm.
Proof:

Assume an orphan message M exit between thread Y and Z. Without the loss of generality, consider Z as the sender and Y as the receiver. By definition of orphan message, M must be sent after $t_3$ and received before $t_2$. By the checkpoint algorithm, no message is allowed to sent at the interval between tentative point and commit point. Thus, M could only be sent after $t_5$. In other words, $% <![CDATA[ t_5 < t_6 %]]>$ and $% <![CDATA[ t_7 < t_2 %]]>$ .

By checkpoint algorithm, we could obtain the conclusion $% <![CDATA[ t_2 < t_4 < t_5 %]]>$. Revisit the relations at the end of above paragragh, the final time chain would be $% <![CDATA[ t_7 < t_6 %]]>$.

Contradiction: The sending time is larger than the receiving time!