Locking is a mechanism to prevent two or more threads from accessing a shared resource simultaneously.
Locking is a mechanism to prevent two or more threads from accessing a shared resource simultaneously.

Database Locking

Optimistic locking
Pessimistic locking

Optimistic locking

Optimistic locking is a technique used in database systems to prevent concurrent updates to the same data.
Optimistic locking is a technique used in database systems to prevent concurrent updates to the same data.
In optimistic locking, a lock is acquired on the data before updating it.

graph TD
    A[Lock Acquisition] --> B[Check Data Modification]
    B --> C{Modified?}
    C -->|No| D[Acquire Lock]
    D --> E[Single Thread Modification]
    E --> F[Prevent Concurrent Updates]
    F --> G[Maintain Data Consistency]
    C -->|Yes| H[Lock Failed]

Pessimistic locking

Pessimistic locking is a technique used in database systems to prevent concurrent updates to the same data.

graph TD
    A[Request Lock] --> B[Wait for Lock]
    B --> C{Lock Available?}
    C -->|Yes| D[Acquire Lock]
    D --> E[Modify Data]
    E --> F[Release Lock]
    F --> G[Maintain Data Consistency]
    C -->|No| H[Keep Waiting]
    H --> B

Key differences

Table to compare the differences between optimistic and pessimistic locking.

Optimistic locking	Pessimistic locking
Lock is acquired before updating the data	Lock is acquired after updating the data
Lock is released after updating the data	Lock is released before updating the data
Lock is released after updating the data	Lock is released before updating the data

Other Terminologies

ACID: Atomicity, Consistency, Isolation, Durability
2PC: Two-phase commit is applied in micro-services or distributed systems to ensure data consistency and integrity - ensure that all transactions are committed or rolled back atomically.
MVCC: Multiversion concurrency control - controlling the concurrent operations via the versioning of data.

Everything Becomes Worst in Distributed Systems

In Saga Pattern, the saga is a sequence of steps that are executed in a specific order. The saga pattern is used to coordinate the execution of multiple transactions or activities in a distributed system.

Saga Pattern