Hi,
please check as root '/var/log/messages', if the database kernel was killed by the Linux operating system. This can happen, if the Linux OS runs out of memory - it then starts a so called 'oom killer' program which identifies suitable processes to kill. As the MaxDB kernel usually allocates a lot of memory (depends on the CACHE_SIZE setting), it is a likely candidate for termination.
If this was indeed the oom killer, you should find some hint in the 'messages' file like:
/var/log/messages
kernel: [33872.707196] Out of memory: kill process 17092 (kernel)
score 958925227 or a child
kernel: [33872.707199] Killed process 17095 (kernel)
If you are an SAP customer, you can find further info in note 1647204.
Thorsten