Recently my friend told me that it is a good idea to turn off swap on linux webservers with enough memory. My server has 12 GB and currently uses 4GB (not counting cache and buffers) under peak load.

His argument was that in a normal situation server will never use all of its RAM so the only way it can encounter OutOfMemory situation is due to some bug/ddos/etc. So in case swap is turned off system will run out of memory that will eventually crash the program hogging memory (most likely the web server process) and probably some other processes. In case swap is turned on it will eat both RAM and swap and eventually will result in the same crash, but before that it will offload crucial processes like sshd to swap and start to do a lot of swap operations resulting in major slowdown. This way when under ddos system may go into a completely unusable condition due to huge lags and I probably will not be unable to log in and kill webserver process or deny all incoming traffic (all but ssh).

Is this right? Am I missing something (like the fact that swap partition is very useful in some way even if I have enough RAM)? Should I turn it off?