Speculation to Increase the Concurrency of Nested Transactions

We have proposed an improved concurrency control protocol for nested transactions based on speculation. In the proposed speculative nested locking (SNL) protocol, whenever a sub-transaction finishes work with a data object (produces after-image), it's parent inherits the lock. The waiting sub-transaction carries out speculative executions by accessing both beforeand after-images of preceding sub-transaction. It then selects appropriate execution after the termination of preceding sub-transactions. In this way, by carrying out multiple executions for a transaction, SNL increases concurrency. The SNL approach requires both extra processing power and main memory to support speculative executions. In this paper, we have presented the SNL approach and explained how it increases both intraand inter-transaction concurrency by trading extra resources as compared to Moss's nested locking protocol.