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Lock Based Protocol
A lock is nothing but a mechanism that tells the DBMS whether a particular data item is being used by any transaction for read/write purpose. As there are two types of operations, i.e. read and write, whose basic nature are dissimilar, the locks for read and write operation might be behave differently.
Read operation performed by dissimilar transactions on the same data item poses less of a challenge. The value of the data item, if constant, can be read by any number of transactions at any given time.
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Exclusive lock It is asked for by a transaction on a data item that it wants to update. No other transaction can put either a shared lock or an exclusive lock on a dat
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intent locking
Sequences Sequences: Automatically produce unique numbers Are sharable Are typically used to make a primary key value Replace application code Speed up t
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