Tuning of Transactions (Cont.) Reducing lock contention Long transactions(typically read-only)that examine large parts of a relation result in lock contention with update transactions E.g.,large query to compute bank statistics and regular bank transactions To reduce contention Use multi-version concurrency control ·E.g,Oracle“snapshots”which support multi-version2PL Use degree-two consistency(cursor-stability)for long transactions Drawback:result may be approximate Database System Concepts-7th Edition 25.9 ©Silberscha乜，Korth and SudarshanDatabase System Concepts - 7 25.9 ©Silberschatz, Korth and Sudarshan th Edition Tuning of Transactions (Cont.) ▪ Reducing lock contention ▪ Long transactions (typically read-only) that examine large parts of a relation result in lock contention with update transactions • E.g., large query to compute bank statistics and regular bank transactions ▪ To reduce contention • Use multi-version concurrency control ▪ E.g., Oracle “snapshots” which support multi-version 2PL • Use degree-two consistency (cursor-stability) for long transactions ▪ Drawback: result may be approximate