Introduction to Error handler

Error Handler are the fifth type of DML_HANDLER. They differ from the mainstream DML_HANDLER in that they are called only when the apply process cannot succeed.
The following table show the difference in usage between the two :

Type of handler	When	Frequency	Comments
DML_HANLDER	Before Apply	ALWAYS called
ERROR_HANLDER	After Apply	ONLY case of problems	error_handler column must = TRUE

In short an Error_handler is called AFTER and CASE OF while a DML_HANDLER is called ALWAYS

It is important to note that you cannot have a DML handler and an error handler simultaneously for the same operation on the same table.

An error handler is a procedure that must be of the following Signature:

PROCEDURE user_procedure ( evt               IN SYS.AnyData,
                           error_stack_depth IN NUMBER,
                           error_numbers     IN DBMS_UTILITY.NUMBER_ARRAY,
                           error_messages    IN emsg_array);