Are you trying to do this while the system load is very high? If that is the case you might be better off killing those processes by process ID number (if you know the PID numbers already as in your example).
In your example:
kill -9 813251 813265
You can check the system load averages as part of the output in the uptime
command
killall -9
should send SIGKILL to your processes, but the process in 813251 is actually /bin/sh not update_db_cache.
You could try to kill every process where update_db_cache shows up:
sudo ps -ef |grep update_db_cache |grep -v grep |awk '{print $2}' |xargs kill -9
If you want to kill the parent PIDs as well (as Andrew B suggests) you could do the following (although I would advise against doing it blinding like this):
ps -ef |grep update_db_cache |grep -v grep |awk '{print $2" "$3}' |xargs kill -9