Efficient update-anywhere replication of queue operations on a replicated message queue

Abstract

Update-anywhere replication of queuing operations on a replicated message queue is performed. A dequeue ready time ('ready time') is associated by each participating persistent storage server with a queue message to be dequeued. Unless a queue message is already locked by a distributed dequeue transaction, a participating leader PSS initiates a distributed dequeue transaction for the queue message once the ready time for the queue message is reached, subject to certain conditions. An initiator PSS is in effect designated for a queue message; the initiator PSS associates a desired ready time for the queue message. The designated PSS is referred to herein as the primary leader PSS and the ready time the primary PSS associates with queue message is referred as the primary ready time. The other participating leader PSSs are backup leader PSSs which serve as backups for dequeuing a queue message. Each backup leader PSS associates a later 'backup ready time' with the queue message. In an embodiment, each backup ready time for a queue message is different. The primary ready time for a queue message together with backup ready times for the queue message form a more or less staggered set of ready times. If the primary leader PSS does not initiate dequeuing of a queue message before a successive backup ready time, the respective backup leader PSS may initiate dequeuing. This measure provides fault tolerance for dequeuing a queue message. Because the ready times are staggered, not all PSSs will initiate dequeuing at more or less the same time. Thus, initiator conflict is substantially reduced while fault tolerance is provided.