Lock-free transactional support for large-scale storage systems

Abstract

Described is a reliable and efficient design for a transactional status oracle ('ReTSO'), which supports large-scale storage systems. ReTSO uses a centralized scheme and implements snapshot isolation, a property that guarantees that read operations read a consistent snapshot of the data store. The centralized scheme of ReTSO enables a lock-free commit algorithm that prevents unreleased locks of a failed transaction from blocking other transactions. Each transaction submits the identifiers of modified rows to the ReTSO, the transaction is committed only if none of the modified rows is committed by a concurrent transaction, and a log of the committed transaction is cached. To recover from failures, before a client is notified of a change, the change cached is first persisted into a write-ahead log, such that the memory state can be fully reconstructed by reading from the write-ahead log. Furthermore, ReTSO implements a lazy, auto-garbage collector hash map that reduces the number of memory accesses per request.