Persistent Messaging Example:funds transfer between two banks Two phase commit would have the potential to block updates on the accounts involved in funds transfer Alternative solution: Debit money from source account and send a message to other site Site receives message and credits destination account Messaging has long been used for distributed transactions (even before computers were invented!) ▣Atomicity issue once transaction sending a message is committed,message must guaranteed to be delivered Guarantee as long as destination site is up and reachable,code to handle undeliverable messages must also be available e.g.,credit money back to source account. If sending transaction aborts,message must not be sent Database System Concepts-7th Edition 23.18 ©Silberscha乜，Korth and SudarshanDatabase System Concepts - 7 23.18 ©Silberschatz, Korth and Sudarshan th Edition Persistent Messaging ▪ Example: funds transfer between two banks • Two phase commit would have the potential to block updates on the accounts involved in funds transfer • Alternative solution: ▪ Debit money from source account and send a message to other site ▪ Site receives message and credits destination account • Messaging has long been used for distributed transactions (even before computers were invented!) ▪ Atomicity issue • once transaction sending a message is committed, message must guaranteed to be delivered ▪ Guarantee as long as destination site is up and reachable, code to handle undeliverable messages must also be available • e.g., credit money back to source account. • If sending transaction aborts, message must not be sent