🔑 OptimisticLockException

Definition: OptimisticLockException is an exception thrown in JPA/Hibernate when optimistic locking fails.

It happens when two or more transactions try to update the same entity simultaneously, and the version check fails.

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1️⃣ Optimistic Locking Concept

• Optimistic locking does not lock rows in the database.
• Each row/entity has a version field (integer or timestamp).

• When updating:

  1. Read the entity with its current version.
  2. Make changes.
  3. When saving, check if the version in DB matches the version read.
  4. If versions match, increment version and save.
  5. If versions don’t match, throw OptimisticLockException.

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2️⃣ Example

@Entity
public class Account {
    @Id
    private Long id;

    private double balance;

    @Version
    private int version;  // Optimistic lock version
}

Scenario:

1. Transaction A reads account version = 1
2. Transaction B reads account version = 1
3. Transaction A updates balance → version increments to 2 → saved successfully
4. Transaction B updates balance → version in DB = 2, but B read version = 1 → OptimisticLockException thrown

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3️⃣ Why it’s useful

• Prevents lost updates in concurrent environments.
• Safer than pessimistic locking for high-concurrency systems.
• Works well when conflicts are rare, since no DB row locks are held.

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4️⃣ How to handle it

1. Retry transaction: Often, just retrying the operation works.
2. Notify user: Let the user know their changes conflicted.
3. Merge changes: Apply conflict resolution logic manually.

try {
    accountRepository.save(account);
} catch (OptimisticLockException e) {
    // retry or show error
}

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5️⃣ Key Points

• Uses a version column (@Version) in JPA/Hibernate.
• Exception occurs at commit/update, not at read.
• Suitable for high-concurrency systems where conflicts are rare.
• Lightweight compared to pessimistic locking.

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💡 Analogy:

Think of it like signing a document:

• You read the latest version of the doc.
• Make your edits.
• When saving, the system checks if the doc has been edited since you read it.
• If yes → conflict → OptimisticLockException.

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