How Can You Implement Optimistic Locking in MySQL?

Optimistic Locking in MySQL

Optimistic locking is a practice used in concurrency control to prevent multiple users from updating the same data simultaneously. Unlike pessimistic locking, which assumes that conflicts will occur and locks data at the beginning of a transaction, optimistic locking assumes that conflicts are rare and allows updates without locking.

Implementation in MySQL

MySQL does not natively implement optimistic locking. However, it can be implemented using standard SQL instructions and the version column approach:

<code class="sql">CREATE TABLE theTable (
    id INT NOT NULL AUTO_INCREMENT,
    val1 INT NOT NULL,
    val2 INT NOT NULL,
    version INT NOT NULL DEFAULT 0
);</code>

Optimistic Locking Query:

<code class="sql">UPDATE theTable
SET val1 = @newVal1,
    val2 = @newVal2,
    version = version + 1
WHERE id = @id
AND version = @oldVersion;</code>

Checking for Conflicts:

After the update, the AffectedRows value is checked:

• If AffectedRows == 1, the update was successful without conflicts.
• If AffectedRows == 0, a conflict occurred, and the update failed.

Isolation Levels

Transaction isolation levels play a role in optimistic locking. In READ_COMMITTED isolation level, other processes cannot read uncommitted updates, which prevents conflicts from occurring.

Limitations

• Scalability: Optimistic locking can become less effective in high-concurrency environments where conflicts are more likely.
• Data Loss: If a conflict occurs, data changes made by other users may be lost.

When to Use

Optimistic locking is suitable for situations with infrequent updates and a low probability of conflicts. It is often used in web applications where short user sessions reduce the likelihood of concurrent updates.

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