Difference between SET autocommit=1 and START TRANSACTION in mysql (Have I missed something?)

sql

transaction-management

mysql

database-operations

byAlex Kataev·Dec 3, 2024

SET autocommit=1 switches the database into auto-pilot mode, where every SQL command is automatically committed. On the other hand, START TRANSACTION sets up a transactional playground, grouping all commands until an explicit COMMIT brings it back to reality.

Auto-pilot (Autocommit) mode on:

SET autocommit=1; -- SQL statements are now being auto-committed
INSERT INTO table_name ...; -- Directly committed, not a moment to spare

Transactional playground:

START TRANSACTION; -- Time to group statements
INSERT INTO table_name ...; -- Hangs tight until the explicit COMMIT
COMMIT; -- Playground time over, COMMIT to actual data

Choosing Tarzan or Jane: SET `autocommit=0` vs `1`

SET autocommit=0 is like Tarzan swinging on different branches (SQL operations) of the database before finally landing (committing). SET autocommit=1 is more like Jane, who takes a comfortable walk (single operation) and immediately marks the end of her path (commit).

In short, autocommit=0 lets you keep the hold on the transaction until you're sure and COMMIT. It allows you to review and test UPDATE and DELETE operations within the safe confines of a SELECT statement before finalizing them.

Remember, after swinging from branch to branch like Tarzan, always LOCK TABLES to ensure data integrity and UNLOCK TABLES only after a satisfying COMMIT.

Team InnoDB vs Team MyISAM: Transaction strategies

Team InnoDB: The transactional all-stars

InnoDB standing strong with its ACID-compliant transactions encourages START TRANSACTION for a grouped approach towards SQL operations. It’s all or none here!

START TRANSACTION; -- Gathering SQL operations
-- Multiple SQL operations happening under the hood…
COMMIT; -- Shouting COMMIT only if it is all flawless

Team MyISAM: Autocommit and table-locking for the win

MyISAM, while lacking transactional superpowers like InnoDB, uses the autocommit wand and the table-locking shield for protection.

SET autocommit=0; -- Turns off autocommit
LOCK TABLES table_name WRITE; -- Locks the table for operations
-- SQL operations happening in the LOCKED environment
COMMIT; -- Alright, COMMIT the changes, I double-checked my codes!
UNLOCK TABLES; -- Finally, the tables are free

Note: MyISAM tables being a bit overzealous, commit any previous uncommitted changes before any table lock.

Eyes on the ball: Understanding isolation levels

Isolation levels dictate how the transactions see the data. When autocommit is on hiatus, the default isolation level significantly determines whether your transactions say peekaboo or hide and seek.

READ UNCOMMITTED: Dirty reads? Yes, please! Shows changes not committed yet.
READ COMMITTED: Dirty reads? Nope! Shows changes only if committed.
REPEATABLE READ: Call it Deja Vu. InnoDB’s default level. Shows the same data on repeated reads within the same transaction.
SERIALIZABLE: The GateKeeper. Locks data read by a transaction keeping others at bay till it's done.

There’s no one-size-fits-all. Choose the isolation level that fits your sneaker.

Best practices for Betty and Veronica style transaction management

Betty Cooper's cautious and meticulous transactions handling:

Spell out transaction boundaries: Use START TRANSACTION and COMMIT / ROLLBACK for clarity.
Test changes before applying: Run SELECT statements to predict and verify.
Refer to source docs: Consult the MySQL Reference Manual for sound advice.
Know your engine: Understand the transactional differences between InnoDB and MyISAM, like knowing the exact amount of caffeine you need.