Editing Isolation (database systems) (section)

===Serializable===
This is the ''highest'' isolation level.

With a lock-based [[concurrency control]] DBMS implementation, [[serializability]] requires read and write locks (acquired on selected data) to be released at the end of the transaction.  Also ''range-locks'' must be acquired when a [[Select (SQL)|SELECT]] query uses a ranged ''WHERE'' clause, especially to avoid the '''''[[#Phantom reads|phantom reads]]''''' phenomenon.

When using non-lock based concurrency control, no locks are acquired; however, if the system detects a ''write collision'' among several concurrent transactions, only one of them is allowed to commit.  See ''[[snapshot isolation]]'' for more details on this topic.

From : (Second Informal Review Draft) ISO/IEC 9075:1992, Database Language SQL- July 30, 1992:
''The execution of concurrent SQL-transactions at isolation level SERIALIZABLE is guaranteed to be serializable. A serializable execution is defined to be an execution of the operations of concurrently executing SQL-transactions that produces the same effect as some serial execution of those same SQL-transactions. A serial execution is one in which each SQL-transaction executes to completion before the next SQL-transaction begins.''