UNIT III TRANSACTIONS

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 3.10 MULTI-VERSION CONCURRENCY CONTROL

Multi-version Concurrency Control

• The DBMS maintains multiple physical versions of single logical object in the database.

• When a transaction writes to an object, the database creates a new version of that object.

• When a transaction reads an object, it reads the newest version that exists when the transaction started.

• In this technique, the writers don't block readers or readers don't block writer.

• This scheme makes use of:

     i) Locking protocol and

     ii) Timestamp protocol.

• The multiversion is now used in almost all database management system as a modern technique of concurrency control.

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