Database Locks & Isolation Levels

Lock : A software mechanism used to regulate concurrent access to a shared resource.

Lock Granularity : A lock can be placed on the following resources.
1. An indivudual row (Row lock)
2. A data page (Page lock)
3. An Entire Table(Table lock)

Concurrency : The ability of multiple users accesing a resource(data) simultaneously.
The goal should be to have high concurrency without compromising on data consistency.

Transaction : A set of DML Statements that defines a logical unit of work.

Lock Type :

Shared Lock (Read Lock)
Exclusive Lock ( Write Lock)

Lock compatibility

Shared Exclusive
Shared Yes No
Exclusive No No



Isolation Level