Abstract: A method for a secondary host to support continuous availability for an application on a primary virtual machine on a primary host is disclosed. The method includes the secondary host creating a secondary virtual machine that is identical to the primary virtual machine, the secondary host receiving activities of the primary virtual machine from the primary host, the secondary host buffering the activities, and the secondary host determining if the buffered activities are safe to replay. When the buffered activities are determined to be safe to replay, the method includes the secondary host replaying the buffered activities to the secondary virtual machine. When the buffered activities are determined to be unsafe to replay, the method includes the secondary host discarding the buffered activities and setting the secondary virtual machine as a new primary virtual machine to take over a service provided by the application.

Abstract: A process group resource manager for managing protected resources during transaction processing is disclosed. The process group resource manager comprises a first process configured to provide access to a protected resource during one or more transactions, the first process being further configured to construct a transaction record for each respective transaction, wherein each transaction record includes each request message received by the first process and each response message sent by the first process during a particular transaction. The process group resource manager further comprises a second process configured to serially replay the transactions in which the first process participates, the second process being configured to cause a particular transaction to rollback if the replay of that transaction does not match the transaction record constructed by the first process for that transaction.

Abstract: Architecture that reduces data loss resulting from failover in an asynchronous log shipping deployment, but leveraging mid-tier and frontend servers to fill in lost data. In an asynchronous log shipping operation, a replication component asynchronously replicates messaging data to a backend server in accordance with one or more replication operations, which can be updates to databases on the backend server. These databases can include messaging data, such as email address books, mailboxes, etc. A history component maintains a history of replication operations on a frontend server. In the event of a lossy failover, a replay component is used for replaying the replication operations from the history to the backend server.