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DBMS BCA Unit-5 Transaction - Definition Transaction - Examples COMMIT and ROLLBACK Properties of a Transaction States of Transactions The Concurrent Transactions Transactions - Lost Updates Transactions - Unrepeatable Reads Transactions - Dirty Reads Transactions - Inconsistent Analysis Serialisable Schedule Serial and Interleaved Schedule Precedence Graph Algorithm Precedence Graph Construction Non Serializable Schedule Locking Protocol Locks and Types of Locks Binary Locks Multiple-Mode Locks Shared and Exclusive Locks Two Phase Locking (2PL) Types of Two Phase Locking Database Security Goals Types of Database Security Threats to Databases Database Security & Authorization Subsystem Discretionary Security Mechanisms Mandatory Security Mechanisms Control Measures Access Control Inference Control Flow Control Data Encryption Database Security and the DBA DBA - Privileged Commands DBA Role Access Control, User Accounts and Database Audits System Log Database Audit Audit Trail Sensitive Data and Types of Disclosures Sensitive Data - Classification Factors Factors - Data is Safe Discretionary Access Control in a Database Account Level Privileges Relation Level Privileges Access Matrix Model Privileges on Relations


Properties of a Transaction

  • Atomicity
    It defines a transaction to be a single unit of processing. In other words, either a transaction will be done completely or not at all.

  • Consistency
    This property ensures that a complete transaction takes a database from one consistent state to another consistent state. If a transaction fails even then the database should come back to a consistent state.

  • Isolation or Independence
    The isolation property states that the updates of a transaction should not be visible till they are committed. Isolation guarantees that the progress of a transaction do not affect the outcome of another transaction.

  • Durability or Permanence
    This property necessitates that once a transaction has committed, the changes made by it be never lost because of subsequent failure.