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Transaction Model

 

There are two basic operations in a transaction.

  1. read (X): Transfers the data item X from the database to a variable.
  2. write (X): Transfers the value in the variable X in the main-memory buffer of the transaction that executes the write to the data item X in the database.

 

Example-1:  Transfer an amount of Rupees 50 from Account-A to Account-B.

T1  :   read A ;

 A = A – 50 ;

 write A ;

 read B ;

 B = B + 50 ;

 write B ;

 

Storage Structure

 There are three types of storage.

  1. Volatile Storage: Information residing in volatile storage does not usually survive system crashes. Examples of such storage are main memory and cache memory.
  2. Non-Volatile Storage: System crashes do no serious harm to information kept in non-volatile storage. Examples of such storage are secondary storages.
  3. Stable Storage: Information that is present inside stable storage always retains and is never lost. Example of such storage is replicating the information in several non-volatile storages.

 

Reference Link

Transaction Model