Single-Lock-Manager Approach In the single lock-manager approach,lock manager runs on a single chosen site,say S; All lock requests sent to central lock manager The transaction can read the data item from any one of the sites at which a replica of the data item resides. Writes must be performed on all replicas of a data item Advantages of scheme: Simple implementation Simple deadlock handling Disadvantages of scheme are: Bottleneck:lock manager site becomes a bottleneck Vulnerability:system is vulnerable to lock manager site failure. Database System Concepts-7th Edition 23.24 ©Silberscha乜，Korth and SudarshanDatabase System Concepts - 7 23.24 ©Silberschatz, Korth and Sudarshan th Edition Single-Lock-Manager Approach ▪ In the single lock-manager approach, lock manager runs on a single chosen site, say Si • All lock requests sent to central lock manager ▪ The transaction can read the data item from any one of the sites at which a replica of the data item resides. ▪ Writes must be performed on all replicas of a data item ▪ Advantages of scheme: • Simple implementation • Simple deadlock handling ▪ Disadvantages of scheme are: • Bottleneck: lock manager site becomes a bottleneck • Vulnerability: system is vulnerable to lock manager site failure