| 摘要 |
A system for maintaining reliable packet distribution in a ring network with support for strongly ordered, nonidempotent commands. Each consumer node on the network maintains a record of the sequence of packets that have passed through that node, and the state of each of the packets at the time it passed through, including a record of the last known good packet and its sequence number. When a producer node detects an error condition in an acknowledgment for a packet, resends all packets beginning with the last known good packet. Each consumer node is able to process or reject the resent packets, including packets that may already have been processed, which it is aware of due to the packet and state records for all packets. Strong ordering is thus supported, since the sending order of packets can be maintained for processing due to the resends, and nonidempotent commands are supported due to the consumer nodes' ability to determine whether they have already processed a given packet, and to send an acknowledge-done reply if that is the case. The system is equipped to operate successfully in the presence of a failed or very busy node by maintaining a queue of busy acks from each node, or from nodes that are particularly busy, and when the queue is full taking steps to bypass the busy or failed node. Alternatively, the system can detect that some predetermined period of time has passed during which either no response or only busy responses have been received from a given node, and at that point determine to effectively bypass the node for future transactions, at least for some timeout period, so that packet transactions for the rest of the network can proceed unhindered by the ill-behaved node.
|
