Conversion: multi-version concurrency control for main memory segments

We present Conversion, a multi-version concurrency control system for main memory segments. Like the familiar Subversion version control system for files, Conversion provides isolation between processes that each operate on their own working copy. A process retrieves and merges any changes committed to the trunk by calling update(), and a call to commit() pushes any local changes to the trunk. Conversion operations are fast, starting at a few microseconds and growing linearly (by less than 1 μs) with the number of modified pages. This is achieved by leveraging virtual memory hardware, and efficient data structures for keeping track of which pages of memory were modified since the last update. Such extremely low-latency operations make Conversion well suited to a wide variety of concurrent applications. Below, in addition to a micro-benchmark and comparative evaluation, we retrofit Dthreads [28] with a Conversion-based memory model as a case study. This resulted in a speedup (up to 1.75x) for several benchmark programs and reduced the memory management code for Dthreads by 80%.