Excite-Vm: Extending The Virtual Memory System To Support Snapshot Isolation Transactions

Multi-core programming remains a major software development and maintenance challenge because of data races, deadlock, non-deterministic failures and complex performance issues. In this paper, we describe EXCITE-VM, a system that provides snapshot isolation transactions on shared memory to facilitate programming and to improve the performance of parallel applications. With snapshots, an application thread is not exposed to the committed changes of other threads until it receives the updates by explicitly creating a new snapshot. Snapshot isolation enables low overhead lockless read operations and improves fault tolerance by isolating each thread from the transient, uncommitted writes of other threads. This paper describes how EXCITE-VM implements snapshot isolation transactions efficiently by manipulating virtual memory mappings and using a novel copy-on-read mechanism with a customized page cache. Compared to conventional software transactional memory systems, EXCITE-VM provides up to 2.2x performance improvement for the STAMP benchmark suite and up to 1000x speedup for a modified benchmark having long running read-only transactions. Furthermore, EXCITE-VM achieves a 2x performance improvement on a Memcached benchmark and the Yahoo Cloud Server Benchmarks. Finally, EXCITE-VM improves fault tolerance and offers features such as low-overhead concurrent audit and analysis.