Speculation based nested locking protocol to increase the concurrency of nested transactions

The authors propose an improved concurrency control protocol based on speculation for nested transactions and explain how it increases both intraand inter-transaction concurrency as compared to J.E.B. Moss´s (1985) nested locking protocol. 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 before- and after-images of preceding sub-transaction and selects appropriate execution after the termination of the preceding subtransaction. In this way, SNL allows multiple executions to be carried out for a transaction by trading extra processing and main memory resources to increase concurrency