Logical and Physical Versioning in Main Memory Databases

We present a design for multi-version concurrency control and recovery in a main memory database, and describe logical and physical versioning schemes that allow read-only transactions to execute without obtaining data item locks or system latches. These schemes enable a system to guarantee that updaters will never interfere with read-only transactions, and that read-only transactions will not be delayed as long as the operating system provides them with sufficient cycles. Our contributions include several space saving techniques for the main memory implementation. We extend the T-tree index structure (designed for main-memory databases) to support concurrent access and latch-free traversals, and demonstrate the performance benefits of our extensions. Some of these schemes have been implemented on a widely-used software platform within Bell Labs., and the full scheme is implemented in the Dali main memory storage manager.