Database.Advanced.Is MVCC implementation of optimisti lock ?

✅ Short Answer:

MVCC is a form of optimistic concurrency control, but not all optimistic locking is MVCC.

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🧠 Detailed Comparison

Feature	MVCC	Optimistic Locking (manual)
Type	System-level concurrency control	Application or ORM-level concurrency control
Uses versions?	✅ Yes — creates versions for each write	✅ Yes — usually uses a version number or timestamp
Conflict detection	Implicit — via visibility rules in DB engine	Explicit — you check version before writing
Locks used?	❌ No locks for reads	❌ No locks — check happens only at write time
When conflicts are handled	At commit time or during snapshot evaluation	When updating the row and version doesn’t match

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🧩 Example

🔹 MVCC (e.g., in PostgreSQL):

• Transaction A starts and reads snapshot.
• Transaction B updates the row and commits.
• A doesn’t see B’s changes until it finishes or restarts.
• If A tries to write based on old data, conflict may arise.

🔹 Optimistic Locking (custom or ORM-based):

• Row has a version or updated_at column.
• You read: version = 1
• You write: UPDATE ... WHERE id = ? AND version = 1
• If version was incremented by someone else, 0 rows updated → conflict.

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🏗️ MVCC = Optimistic at Engine Level

• MVCC handles versioning and snapshot isolation internally (transparent to you).
• It works great for systems with many reads and few write conflicts.
• MVCC is automated, while optimistic locking often requires manual setup in app logic.

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✅ Summary:

MVCC is a built-in, low-level implementation of optimistic concurrency control, while optimistic locking usually refers to a higher-level, manual strategy implemented in application logic (e.g., via Hibernate, Spring Data, etc.).