Transactions in MySQL

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A transaction groups multiple SQL statements into a single unit of work. Either all of them succeed, or none of them do. Without transactions, a failure halfway through a multi-step operation — a payment, a transfer, an order — can leave your data in a broken intermediate state.

The Basics: BEGIN, COMMIT, ROLLBACK

START TRANSACTION;

UPDATE accounts SET balance = balance - 100 WHERE id = 1;  -- debit Alice
UPDATE accounts SET balance = balance + 100 WHERE id = 2;  -- credit Bob

COMMIT;  -- both changes are saved

If something goes wrong between the two updates:

START TRANSACTION;

UPDATE accounts SET balance = balance - 100 WHERE id = 1;

-- error occurs here, or you decide to cancel

ROLLBACK;  -- neither change is saved — balance unchanged

ROLLBACK undoes everything back to the START TRANSACTION. The database is left as it was before the transaction began. BEGIN and START TRANSACTION are equivalent. Both start a new transaction.

Autocommit

By default, MySQL runs in autocommit mode — each statement is its own transaction, committed immediately. That’s why DELETE FROM orders WHERE id = 5 takes effect right away without an explicit COMMIT. Calling START TRANSACTION temporarily suspends autocommit for the duration of that transaction.

-- Check current autocommit setting
SHOW VARIABLES LIKE 'autocommit';

-- Disable autocommit for the session
SET autocommit = 0;

-- Now every statement is part of a transaction until you COMMIT or ROLLBACK
UPDATE accounts SET balance = balance - 100 WHERE id = 1;
UPDATE accounts SET balance = balance + 100 WHERE id = 2;
COMMIT;

Disabling autocommit means you must explicitly COMMIT or ROLLBACK after every operation. If you disconnect without committing, MySQL rolls back any open transaction.

Isolation Levels

When multiple transactions run at the same time, isolation levels control what each transaction can see from the others. MySQL’s default is REPEATABLE READ.

Level	Dirty Reads	Non-repeatable Reads	Phantom Reads
`READ UNCOMMITTED`	Possible	Possible	Possible
`READ COMMITTED`	Prevented	Possible	Possible
`REPEATABLE READ`	Prevented	Prevented	Prevented*
`SERIALIZABLE`	Prevented	Prevented	Prevented

*InnoDB’s REPEATABLE READ prevents phantom reads via gap locks, which is stricter than the SQL standard requires. READ COMMITTED is a common choice for applications that prioritize throughput. It prevents dirty reads (seeing uncommitted data from other transactions) but allows non-repeatable reads (the same row read twice in one transaction might return different values if another transaction committed between the reads).

-- Set isolation level for the current session
SET SESSION TRANSACTION ISOLATION LEVEL READ COMMITTED;

-- Or for the next transaction only
SET TRANSACTION ISOLATION LEVEL READ COMMITTED;
START TRANSACTION;
-- ...

Savepoints

Savepoints let you roll back part of a transaction without abandoning the whole thing:

START TRANSACTION;

INSERT INTO orders (customer_id, amount) VALUES (1, 99.00);
SAVEPOINT after_order;

INSERT INTO order_items (order_id, product_id) VALUES (LAST_INSERT_ID(), 42);

-- something went wrong with the item — roll back just this part
ROLLBACK TO SAVEPOINT after_order;

-- the order is still there; we can retry the item insert
INSERT INTO order_items (order_id, product_id) VALUES (LAST_INSERT_ID(), 43);

COMMIT;

What Transactions Don’t Cover

Not all MySQL statements can be rolled back. DDL statements (CREATE TABLE, ALTER TABLE, DROP TABLE) cause an implicit commit — MySQL commits any open transaction before executing them, and the DDL itself cannot be rolled back.

START TRANSACTION;
INSERT INTO orders (customer_id, amount) VALUES (1, 99.00);

DROP TABLE temp_data;  -- implicit commit happens here — the INSERT is committed

ROLLBACK;  -- nothing to roll back; everything was already committed

Frequently Asked Questions

What happens if a transaction is never committed?

If you close the connection without committing, MySQL automatically rolls back the open transaction. If the server crashes, InnoDB’s redo log recovers committed transactions and rolls back uncommitted ones on startup.

Can I use transactions with MyISAM?

No. Transactions require a transactional storage engine. InnoDB (MySQL’s default engine) fully supports transactions. MyISAM does not — statements against MyISAM tables take effect immediately and can’t be rolled back.

How long can a transaction stay open?

Technically as long as needed, but long-running transactions hold locks and consume undo log space, which causes performance problems for other transactions. The innodb_lock_wait_timeout variable (default: 50 seconds) controls how long a transaction waits for a lock before returning an error. Keep transactions short and commit as soon as the work is done.

Troubleshooting

Problem	Solution
Changes aren’t persisting	Check if autocommit is off — you may need to call `COMMIT` explicitly
`ROLLBACK` has no effect	A DDL statement (`CREATE`, `ALTER`, `DROP`) caused an implicit commit mid-transaction
Transaction is blocking other queries	A long-running transaction is holding locks — commit or roll back promptly; check `SHOW ENGINE INNODB STATUS` for lock info
`ERROR 1205: Lock wait timeout exceeded`	Another transaction holds a conflicting lock; retry after the blocking transaction completes

Getting Started

Server Development

Extensions

Using Extensions

Creating Extensions

VillageSQL is a drop-in replacement for MySQL with extensions.

The Basics: BEGIN, COMMIT, ROLLBACK

Autocommit

Isolation Levels

Savepoints

What Transactions Don’t Cover

Frequently Asked Questions

What happens if a transaction is never committed?

Can I use transactions with MyISAM?

How long can a transaction stay open?

Troubleshooting

See also

VillageSQL is a drop-in replacement for MySQL with extensions.

​The Basics: BEGIN, COMMIT, ROLLBACK

​Autocommit

​Isolation Levels

​Savepoints

​What Transactions Don’t Cover

​Frequently Asked Questions

​What happens if a transaction is never committed?

​Can I use transactions with MyISAM?

​How long can a transaction stay open?

​Troubleshooting

​See also

The Basics: BEGIN, COMMIT, ROLLBACK

Autocommit

Isolation Levels

Savepoints

What Transactions Don’t Cover

Frequently Asked Questions

What happens if a transaction is never committed?

Can I use transactions with MyISAM?

How long can a transaction stay open?

Troubleshooting

See also