UNIX performs memory management in a very 'traditional' way - programs are loaded into memory in pages until the working set is established, and when there is a demand for more memory space, pages which have been least recently used are simply discarded if they have not been altered, or written back to disk if they have. Different UNIX versions have variations on this basic pattern, but most of them keep to this strategy right up to the point where memory is around 90% full or higher. At that stage, what is known as 'Desperation Swapping' can occur. ALL of the memory pages for a process get written out to the swap space on disk. This obviously brings the process in question to a complete stop, but equally seriously can create an I/O bottleneck on the swap device. If there are also filesystems being used by other processes on that disk, these processes can be seriously affected, and performance can generally degrade very badly.

If you have Athene check the 'Swapping Overview' table in Athene Analyst for consistent swap outs being performed. Another measurement to check is the 'Processes Waiting' column in the 'CPU Overview' table. This is a measure of the number of processes unable to run because they are swapped out. If this value is consistently non-zero, it may be an indication of Desperation Swapping.