Asynchronous replica management in shared nothing architectures

An improved transaction processing system of the type which includes:

• a plurality of transaction processors connected by a communication network, each of said processors having its own private storage;
• said transaction processing system having at least one partition of data which is subpartitioned into pages, said partition of data including a primary replica of said partition and a secondary replica of said partition, said primary replica being stored in said private storage of one of said processors and said secondary replica being stored in said private storage of another one of said processors;
• and
• a non-volatile log, said transaction processing system using a Write-Ahead Log protocol in which a modification to a page in said partition is not considered made until said modification is stored in said log;
• wherein the improvement comprises:
• means for generating a response indicating to a transaction requestor that a requested transaction on the primary replica has completed;
• means for updating said secondary replica from said primary replica by asynchronously sending modified pages from said primary replica to said secondary replica independently of the generation of the response by the means for generating and without imposing any page sending order or timing constraint;
• means for keeping track of the pages of said partition which have been modified in said primary replica and not yet modified in said secondary replica;
• and
• means for making said log accessible to both said processors which are storing a replica of said partition,
• whereby said secondary replica is maintained without imposing delay upon the processing of transactions on said primary replica by said one processor.