Hello,
A study on in memory databases (ScaMMDB: Facing Challenge of Mass Data Processing with MMDB), says the following about MonetDB:

"the power@size measure of TPC-H shows that it drops as data volume increases. When data volume exceeds 75% of memory capacity, power@size value rapidly decreases
till system crash when data volume exceeds total capacity of memory and swap. So the high performance of MMDB relies on sufficient memory supply. "