Preserving consistency of passively-replicated non-deterministic objects

Abstract

Techniques are provided for executing an operation in which a client invokes a replicated object. According to one technique, a primary replica of a replicated object receives a first request from a client, wherein the first request includes a request identifier. Rather than immediately attempting to process the request, the primary replica determines whether a record exists that corresponds to the request identifier. If a record exists that corresponds to the request identifier, then the primary replica responds to the first request with a reply associated with the record. If no record exists that corresponds to the request identifier, then the primary replica performs the steps of: starting a transaction; as part of the transaction, processing the request; as part of the transaction, storing a record associated with the request identifier and a reply to the request; committing the transaction; and delivering the reply to the client. The client may itself be a replicated object. If the client is nondeterministic, then the transaction initiated by the primary replica may be a nested transaction relative to a transaction executed by the client, or be executed as part of the same transaction as the client. If the transaction executed by the primary replica is executed as part of the same transaction as the client, then a savepoint may be established before the primary replica processes the request, so that a failure will not necessarily require all processing performed by the client to be rolled back.