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The essence of a transaction is that it groups multiple steps into a single, all-or-nothing operation. Drizzle is a transactional database by default and by design, meaning that changes and queries to the database appear to be Atomic, Consistent, Isolated, and Durable (ACID). This means that Drizzle implements `serializable <http://en.wikipedia.org/wiki/Serializability>`_, ACID transactions, even if the transaction is interrupted.
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Transactions are a group of operations that form tasks and stores them as a single operation, or if that operation is not possible it removes all changes attempted. Transactions are controlled via START TRANSACTION, ROLLBACK, and COMMIT. Savepoints are implemented to allow for a lower level of granularity.
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A COMMIT statement ends a transaction within Drizzle and makes all changes visible to other users. The order of events is typically to issue a START TRANSACTION statement, execute one or more SQL statements, and then issue a COMMIT statement. Alternatively, a ROLLBACK statement can be issued, which undoes all the work performed since START TRANSACTION was issued. A COMMIT statement will also release any existing savepoints that may be in use.
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Drizzle can operate in an autocommit mode, where each statement is committed at the end of statement, via: ::
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Transactional DDL is currently not supported, although it may be in the future. This means that although currently you will get a ER_TRANSACTION_DDL_NOT_SUPPORTED error message if you try and execute DDL statements within a transaction, in future versions of Drizzle they may succeed.
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Currently DDL operations are performed as a single transaction, this limitation will be lifted in the future.
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For various reasons, Drizzle may have to ROLLBACK a statement or transaction
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docs/transactional.rst
