A serializable transaction is a type of database transaction that guarantees that the concurrent execution of multiple transactions will produce the same result as if the transactions were executed one at a time in some serial order. This means that the isolation level of a serializable transaction is the highest level of isolation and it prevents conflicts such as "dirty reads", "non-repeatable reads", and "phantom reads".
There are four main isolation levels defined by the SQL standard:
Read Uncommitted: The lowest isolation level, where a transaction can see any changes made by other transactions, even if those changes have not been committed yet. This can lead to "dirty reads," where a transaction reads data that has been changed but not yet committed.
Read Committed: A slightly higher isolation level, where a transaction can only see changes made by other transactions that have been committed. This prevents dirty reads, but can still lead to "non-repeatable reads" where a query returns different results depending on when it is executed.
Repeatable Read: A higher isolation level, where a transaction can only see changes made by other transactions that have been committed. In addition, this isolation level prevents non-repeatable reads by ensuring that if a transaction reads a piece of data multiple times, it will get the same value back each time.
Serializable: The highest isolation level, where a transaction can only see changes made by other transactions that have been committed. In addition, this isolation level prevents non-repeatable reads and "phantom reads" by ensuring that no other transactions can modify or insert data that would be visible to the current transaction.