Locked Records (Magic xpa 4.x)

During the course of this section we discussed locked records or rows as they are referred to in the SQL world. When a record is locked, what data another user will actually see depends on the isolation level defined and on the RDBMS you are using. There are three situations that may occur:

• The data is locked. The second user will either receive a message or will have to wait for the data to be released. In Magic xpa, the user will receive a message: “Waiting for locked record”.

• The data that will be displayed is the modified data (the “dirty read” situation).

• The data that will be displayed is the data that was there before the lock was initiated, in other words the data as it was before the transaction was initiated (what is known as the "Before Image").

This section touched briefly on isolation levels. There are actually 4 isolation levels in which you can define how the processes interact with one another. For more information about isolation levels please refer to the reference guide of your RDBMS.