Why does TRANSACTION / COMMIT improve performance so much with PHP/MySQL (InnoDB)?

Solution:

  1. Please check this link:https://dev.mysql.com/doc/refman/5.5/en/optimizing-innodb-transaction-management.html

    InnoDB must flush the log to disk at each transaction commit if that transaction made modifications to the database. When each change is followed by a commit (as with the default autocommit setting), the I/O throughput of the storage device puts a cap on the number of potential operations per second.

  2. Big transactions may affect performance during commit (check above)
  3. Only in case of rollback, however it may be optimized using some settings (check the link)