Microsoft

A database system optimized for in-memory storage can support much higher transaction rates than current systems. However, standard concurrency control methods used today do not scale to the high transaction rates achievable by such systems. In this pa-per we introduce two efficient concurrency control methods spe-cifically designed for main-memory databases. Both use multiver-sioning to isolate read-only transactions from updates but differ in how atomicity is ensured: one is optimistic and one is pessimistic. To avoid expensive context switching, transactions never block during normal processing but they may have to wait before com-mit to ensure correct serialization ordering. We also implemented a main-memory optimized version of single-version locking. Ex-perimental results show that while single-version locking works well when transactions are short and contention is low perfor-mance degrades under more demanding conditions. The multiver-sion schemes have higher overhead but are much less sensitive to hotspots and the presence of long-running transactions. 1