EXACTLY ONCE SEMANTICS

摘要

An exactly once semantics (EOS) system of a storage input/output (I/O) stack implements a technique ensuring that non-idempotent operations occur exactly once in a storage system embodied as a node of a cluster. Illustratively, a first layer of the storage I/O stack may act as a client issuing a non-idempotent operation to second layer of the stack, which may act as a server. According to the technique, the EOS system may wrap (i.e., encapsulate) the non-idempotent operation within a transaction embodied as an EOS transaction data structure having a transaction identifier that uniquely identifies the transaction. The server may complete the transaction and reply with a result to the client, which may acknowledge receipt of the reply. In response to a crash and subsequent recovery of the node, the EOS system may determine whether the transaction had completed prior to the crash. If so, the EOS system ensures that the transaction is not re-played (re-executed). Otherwise, the EOS system allows execution of the transaction such that the transaction occurs exactly once.

主权项

1. A method comprising:
receiving a write request directed towards a storage container, the write request having data, the write request processed at a storage system having a memory and a processor; creating a first transaction at a client process of the storage system, the first transaction having a first operation to store the data and including a unique transaction identifier (ID), the first operation stored to a first log maintained by the client process; sending the first transaction to a server process of the storage system; processing the first transaction at the server process, wherein the data is deduplicated with an extent stored on a storage array of storage devices attached to the storage system, wherein a first persistent state associated with the first transaction is maintained by the server process; sending a first reply for the first transaction from the server process to the client process; and acknowledging the first reply by the client process to the server process, wherein the server process removes the first persistent state associated with the first transaction such that the first operation is executed only once by the storage system.