LSP4YOU - Learner's Support Publications

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

Binary Locks

This locking mechanism has two states for a data item:

Locked
Unlocked

Consider the following schedules:
Incorrect Locking

The above locking method will not solve the problem of concurrent transactions. So locking should be done with some logic in order to make sure that locking results in no concurrency related problem.

Thus, the locking as above when we obtain all the locks at the beginning of the transaction and release them at the end ensures that transactions are executed with no concurrency related problem. However, such a scheme limits the concurrency.