This message is indicates that the internal storage is almost exhausted.
The command cleanup deletes all data which have been written to a disk file and which are currently not displayed. After the data are internally deleted, cleanup does a compress (garbage collection). In fact, cleanup is automatically executed at the end of each scan which is started from the Scan widget.
The inspect the amount of free memory: * = memory_free()
.
The inspect the amount of total memory: * = memory_total()
.