MySQL Transactions vs. Table Locking: Which Method Ensures Database Integrity?

MySQL: Transactions vs. Locking Tables in Database Integrity

Key Difference and Synchronization

When aiming to ensure database integrity and synchronization between SELECT and UPDATE operations, the key difference between transactions and locking tables lies in their purpose:

• Locking Tables: Prevents concurrent database users from modifying or interfering with locked rows or tables.
• Transactions: Ensures that multiple changes to the database form a consistent and correct state, regardless of concurrent operations.

SELECT... FOR UPDATE or LOCK IN SHARE MODE

Using SELECT... FOR UPDATE or SELECT... LOCK IN SHARE MODE can prevent other connections from acquiring write locks on the same row, ensuring consistency during the SELECT and UPDATE execution.

Example Scenario for Synchronization

Consider the following scenario in MySQL:

SELECT * FROM table WHERE (...) LIMIT 1
if (condition passes) {
   // Update row I got from the select 
   UPDATE table SET column = "value" WHERE (...)
   ... other logic (including INSERT some data) ...
}

Achieving Synchronization with Transactions

To achieve synchronization in this scenario using transactions, follow these steps:

1. Start a Transaction: Begin a transaction by executing START TRANSACTION.
2. Perform SELECT and UPDATE: Execute the SELECT and UPDATE operations within the transaction.
3. Commit or Rollback: If all operations complete successfully, commit the transaction using COMMIT. Otherwise, rollback the transaction to its initial state using ROLLBACK.

Advantages of Transactions

Transactions offer several advantages over locking tables:

• Atomicity: Ensures that all operations within the transaction either succeed or fail as a unit, maintaining database integrity.
• Isolation: Prevents simultaneous access and operations from interfering with each other.
• Durability: Guarantees that committed changes become permanent in the database, ensuring transaction recovery in case of system failures.

Combining Transactions and Locking

In situations where maximum concurrency is needed during a transaction, a combination of transactions and table locking can be employed to prevent deadlocks and ensure proper synchronization.

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