Indexing for multiversion locking: alternatives and performance evaluation

Multiversion two phase locking (MV2PL) provides online serializable queries without introducing the long blocking delays that can occur with conventional two phase locking (2PL). MV2PL requires indexing structures, however, that are capable of supporting multiple versions of data. We present several options for extending single version indexing schemes for use with MV2PL. These basic approaches are largely orthogonal to the underlying indexing structure (e.g., hashing or B+ trees). The options considered differ in where they place version selection information (i.e., references to individual versions); this information is placed either with the data or with the index entries of one or more of the indices. We also present the results from a performance study that show that placing the version selection information with the data is usually the best option, since it keeps the indices smaller and thus enables a larger fraction of the index pages to remain cached in the buffer pool.