It is important to remember that, by necessity,
triggers add overhead to the DML statements to which they apply. The actual
amount of overhead will depend upon the nature of the trigger, but—as
all MySQL triggers execute
ROW—the overhead can rapidly accumulate for statements that
process large numbers of rows. You should therefore avoid placing any
expensive SQL statements or procedural code in triggers.
We will look at an example of trigger overhead in Chapter 22.