Pessimistic Concurrency

1. Overview

Definition: Pessimistic concurrency control is a type of database management approach where transactions are assumed to conflict with each other, leading to increased locking mechanisms to maintain data integrity.
Locking Mechanism:
- Exclusive Locks: Prevent other transactions from accessing data until the lock is released.
- Shared Locks: Allow multiple transactions to read data simultaneously but prevent updates.
Advantages:
- Ensures data consistency and integrity by preventing concurrent access issues.
- Reduces the likelihood of lost updates and dirty reads.
Disadvantages:
- Can lead to increased waiting times and decreased system performance due to locks.
- Can result in deadlocks where two or more transactions hold locks that each other needs to proceed.
Use Cases:
- Critical systems where data integrity is paramount (e.g., financial applications).
- Environments with high conflict among transactions.

Locking Mechanism & Advantages: The use of exclusive and shared locks directly correlates to the advantage of data consistency, as it minimizes the risk of conflicting transactions.
Use Cases & Disadvantages: Certain environments may prioritize data integrity at the cost of performance, making pessimistic concurrency suitable for specific applications but problematic in highly concurrent environments.

How do pessimistic concurrency techniques compare to optimistic concurrency approaches in real-world applications?
What are specific examples of systems or applications that effectively use pessimistic concurrency control?
How can deadlocks be mitigated in systems that implement pessimistic concurrency?
What role do transactions and isolation levels play in the implementation of pessimistic concurrency control?
How does the choice between pessimistic and optimistic concurrency impact overall architectural design in software systems?