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Distributed Concurrency Control
additional problem: multiple-copy
consistency problem
Locking protocols
- Centralized 2PL:easy, but central site
becomes a bottleneck.
- Primary copy 2PL:distributing lock manager to a number of sites. a degree ofcentrali-zation, primary copy handle by one site.
- Distributed 2PL: lock manager control data at that site,ROWA protocol
- Majority locking:obtain locks on a majority of copies