STMs in practice: Partial rollback vs pure abort mechanisms

Abstract

SummaryIn this paper, we propose an enhanced Automatic Checkpointing and Partial Rollback (CaPR++) algorithm to realize Software Transactional Memory (STM), that employs partial rollback mechanism for conflict resolution. We have comparatively evaluated the “Abort” and “Partial Rollback” mechanisms for STMs. For purposes of comparison, we have used the state‐of‐the‐art RSTM system and for the “Partial Rollback”, and we have used our earlier CaPR+ algorithm that has been enhanced for our requirements. Note that we have enriched the STAMP benchmarks with varied delayed transaction times. The results obtained demonstrate the effectiveness of the Partial Rollback mechanism over pure abort mechanisms for applications consisting of large transaction delays, with up to 1.6x performance gain for applications with large transactional delays. Our study makes the case for a hybrid system of pure aborts and partial rollbacks, which can extract the benefits of both mechanisms. Keeping in line with our study, we have proposed a hybrid implementation where some of the transactions of an application subscribe to abort mechanisms and the rest to partial rollback. Our initial implementation demonstrates various scenarios where the hybrid approach outperforms the pure abort and partial rollback approaches.