Users report that a database server has become extremely sluggish, with commands taking many seconds to respond. Running 'vmstat 1' shows sustained high values in the 'si' and 'so' columns (hundreds to thousands per second), while CPU 'us' and 'sy' remain low but 'wa' is elevated. 'free -m' shows almost no free memory and swap nearly full. What is the MOST likely cause of the performance degradation?