Most DBMS systems use: –shared locks (SLOCK) for a read lock. –exclusive locks (XLOCK) for a write lock. A lock compatibility matrix tells you which locks are granted and which are not when two (or more) tran
Compatibility of Locks Suppose that there are A and B two different locking modes. If a transaction T1 requests a lock of mode on item Q on which transaction T2 currently hold a lock of mode B. If transaction can be granted lock, in spite of the presence of the mode B lock, then we...
Table-level lock type compatibility is summarized in the following matrix. A lock is granted to a requesting transaction if it is compatible with existing locks, but not if it conflicts with existing locks. A transaction waits until the conflicting existing lock is released. If a lock request c...