Overflow that is not uniformly distributed, that is, it is concentrated around one or two primary pages, is poorly distributed. A classic example of poorly distributed overflow occurs when new rows are added to a table with a key that is greater than all the keys that already exist in the table (for example, a time stamp). If this table has an ISAM structure, the table builds up overflow in the last primary page, and all operations involving this overflow chain can exhibit poor performance. This type of table is best stored as a B-tree or hash.