multiple-mode locks, Database Management System

Multiple-mode locks: It offers two locks: exclusive locks and shared locks. But why do we require these two locks? There are a lot of transactions in the database system that never updates the data values. These transactions can coexist with some other transactions that update the database. In such a condition multiple reads are permitted on a data item, so multiple transactions can lock a data item in the read or shared lock. On the other hand, if a transaction is an updating transaction, i.e., it updates the data items, it has to make sure that no other transaction can access (read or write) those data items that it needs to update. In this situation, the transaction places an exclusive lock on the data items. Therefore, a somewhat higher level of concurrency can be achieved in comparison to the binary locking scheme

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