If every server had plenty of RAM in the real world that does not happen. If for some reason you have a server with too little SWAP or you are hitting the max of the swap. Here is a quick way to add 1GB swap to the server.

dd if=/dev/zero of=/usr/swapfilesys bs=1024 count=1024000
mkswap /usr/swapfilesys
swapon /usr/swapfilesys
swapon -s

Now add the following to the /etc/fstab and you are done.

/usr/swapfilesys	 swap	 swap	 defaults	 0 0