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MySQL View and Modify Transaction Isolation Level

Transaction isolation levels control the degree of isolation between transactions in a database. It's a way to manage how and when the changes made by one transaction become visible to others.

MySQL supports four transaction isolation levels:

  1. READ UNCOMMITTED
  2. READ COMMITTED
  3. REPEATABLE READ (the default)
  4. SERIALIZABLE

Let's understand how to view and modify transaction isolation levels in MySQL.

View the Current Transaction Isolation Level

You can view the current transaction isolation level by running the following command:

SELECT @@tx_isolation;

or, from MySQL 8.0.3 onwards:

SELECT @@transaction_isolation;

Set the Transaction Isolation Level

You can set the transaction isolation level for the next transaction by running the following command:

SET TRANSACTION ISOLATION LEVEL levelName;

Replace levelName with one of the four isolation levels.

For example, to set the transaction isolation level to READ COMMITTED, you would run:

SET TRANSACTION ISOLATION LEVEL READ COMMITTED;

Isolation Levels and Their Effects

  1. READ UNCOMMITTED: The lowest level of isolation. A transaction can see uncommitted changes made by other transactions. This level can lead to issues like dirty reads, non-repeatable reads, and phantom reads.

  2. READ COMMITTED: A transaction can only see changes that have been committed by other transactions. This level prevents dirty reads but can still lead to non-repeatable reads and phantom reads.

  3. REPEATABLE READ: The default level in MySQL. Transactions can't see changes made by others that are committed after the transaction began. This level prevents dirty reads and non-repeatable reads but can still lead to phantom reads.

  4. SERIALIZABLE: The highest level of isolation. Transactions are executed serially. This level prevents dirty reads, non-repeatable reads, and phantom reads but can be slow due to the lack of concurrency.

Remember, increasing the isolation level can increase the consistency of transactions but can also decrease the performance due to less concurrency. Therefore, you should choose an isolation level that appropriately balances consistency and performance for your specific use case.

  1. MySQL view transaction isolation level:

    • View the transaction isolation level in MySQL to understand the current level of isolation for the session.
    -- View current transaction isolation level
SELECT @@GLOBAL.tx_isolation AS 'Global Isolation', @@tx_isolation AS 'Session Isolation';

  2. Check current isolation level in MySQL:

    • Check the current transaction isolation level in MySQL using the SELECT @@tx_isolation; query.
    -- Check current transaction isolation level
SELECT @@tx_isolation;

  3. How to determine transaction isolation level in MySQL:

    • Determine the transaction isolation level in MySQL by querying the tx_isolation system variable.
    -- Determine transaction isolation level
SELECT @@tx_isolation;

  4. Modify transaction isolation level in MySQL:

    • Modify the transaction isolation level in MySQL using the SET TRANSACTION ISOLATION LEVEL statement.
    -- Set transaction isolation level
SET TRANSACTION ISOLATION LEVEL READ COMMITTED;

  5. Change isolation level for a transaction in MySQL:

    • Change the isolation level for a specific transaction in MySQL using the SET TRANSACTION ISOLATION LEVEL statement within the transaction block.
    -- Start transaction with a specific isolation level
START TRANSACTION;
SET TRANSACTION ISOLATION LEVEL SERIALIZABLE;

-- SQL statements

-- Commit or rollback
COMMIT;
-- or
ROLLBACK;

  6. View and update transaction isolation level in MySQL:

    • View and update the transaction isolation level in MySQL using the @@tx_isolation system variable and the SET TRANSACTION ISOLATION LEVEL statement.
    -- View current transaction isolation level
SELECT @@tx_isolation;

-- Set transaction isolation level
SET TRANSACTION ISOLATION LEVEL READ COMMITTED;

  7. Configure transaction isolation level for MySQL:

    • Configure the transaction isolation level for MySQL globally or for a specific session using system variables.
    -- Set global transaction isolation level
SET GLOBAL tx_isolation = 'READ COMMITTED';

  8. Setting global isolation level in MySQL:

    • Set the global transaction isolation level in MySQL using the SET GLOBAL tx_isolation statement.
    -- Set global transaction isolation level
SET GLOBAL tx_isolation = 'READ COMMITTED';

  9. MySQL default transaction isolation level:

    • The default transaction isolation level in MySQL is usually REPEATABLE READ. You can check it using the @@tx_isolation system variable.
    -- Check default transaction isolation level
SELECT @@tx_isolation;
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