How Can Optimistic Locking Be Implemented in MySQL?

Optimistic Locking in MySQL

While MySQL does not natively support optimistic locking, it can be implemented through standard SQL constructs and code logic.

No Locking Approach:

In this approach, no explicit locking is used. However, data consistency is not ensured if multiple users update the same data simultaneously.

SELECT data from theTable WHERE iD = @theId;
{code that calculates new values}
UPDATE theTable
SET val1 = @newVal1,
    val2 = @newVal2
WHERE iD = @theId;

Optimistic Locking Approach:

This approach includes checking for modifications before committing the update. If a modification has occurred, typically determined by row versioning or equality checks, the update is rejected.

SELECT iD, val1, val2
FROM theTable
WHERE iD = @theId;
{code that calculates new values}
UPDATE theTable
SET val1 = @newVal1,
    val2 = @newVal2
WHERE iD = @theId
AND val1 = @oldVal1
AND val2 = @oldVal2;
{if AffectedRows == 1 }
    {go on with your other code}
{else}
    {decide what to do since it has gone bad... in your code}
{endif}

Versioning Optimistic Locking:

Similar to the optimistic locking approach, this technique employs a version column to check for modifications.

SELECT iD, val1, val2, version
FROM theTable
WHERE iD = @theId;
{code that calculates new values}
UPDATE theTable
SET val1 = @newVal1,
    val2 = @newVal2,
    version = version + 1
WHERE iD = @theId
AND version = @oldversion;
{if AffectedRows == 1 }
    {go on with your other code}
{else}
    {decide what to do since it has gone bad... in your code}
{endif}

Transactions and Isolation Levels:

Transactions can be used in conjunction with optimistic locking to ensure data consistency. However, the choice of transaction isolation level can affect the effectiveness of optimistic locking.

Testing and Verification:

To ensure optimistic locking is implemented correctly, it is recommended to perform thorough testing and verification using different scenarios and isolation levels.

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