Persistent Messaging (Cont.) Receiving site may get duplicate messages after a very long delay To avoid keeping processed messages indefinitely Messages are given a timestamp Received messages older than some cutoff are ignored Stored messages older than the cutoff can be deleted at receiving site Workflows provide a general model of transactional processing involving multiple sites and possibly human processing of certain steps E.g.,when a bank receives a loan application,it may need to Contact external credit-checking agencies Get approvals of one or more managers and then respond to the loan application Persistent messaging forms the underlying infrastructure for workflows in a distributed environment Database System Concepts-7th Edition 23.21 @Silberschatz,Korth and SudarshanDatabase System Concepts - 7 23.21 ©Silberschatz, Korth and Sudarshan th Edition Persistent Messaging (Cont.) ▪ Receiving site may get duplicate messages after a very long delay • To avoid keeping processed messages indefinitely ▪ Messages are given a timestamp ▪ Received messages older than some cutoff are ignored ▪ Stored messages older than the cutoff can be deleted at receiving site ▪ Workflows provide a general model of transactional processing involving multiple sites and possibly human processing of certain steps • E.g., when a bank receives a loan application, it may need to ▪ Contact external credit-checking agencies ▪ Get approvals of one or more managers and then respond to the loan application • Persistent messaging forms the underlying infrastructure for workflows in a distributed environment