Different isolation levels may be suitable for different parts of a single transaction. SQL Anywhere allows you to change the isolation level of your database in the middle of a transaction.

When you change the isolation_level option in the middle of a transaction, the new setting affects only the following:

You may want to change the isolation level during a transaction to control the number of locks your transaction places. You may find a transaction needs to read a large table, but perform detailed work with only a few of the rows. If an inconsistency would not seriously affect your transaction, set the isolation to a low level while you scan the large table to avoid delaying the work of others.

You may also want to change the isolation level mid-transaction if, for example, just one table or group of tables requires serialized access.

For an example in which the isolation level is changed in the middle of a transaction, see Tutorial: Phantom rows.

 Changing isolation levels when using snapshot isolation

SET OPTION PUBLIC.allow_snapshot_isolation = 'On';

BEGIN TRANSACTION
    SET OPTION isolation_level = 3;
    INSERT INTO Departments
        ( DepartmentID, DepartmentName, DepartmentHeadID )
        VALUES( 700, 'Foreign Sales', 129 );
    SET TEMPORARY OPTION isolation_level = 'snapshot';
    SELECT * FROM Departments;