Here’s a random interesting car fact. The accelerator pedal only controls how much air makes it to the engine; it opens and closes a flap in the air intake called the throttle body. The car has a sensor that records how much air is coming in, the mass airflow sensor, which is just a wire in the airstream. Electrical resistance in metals is proportional to temperature, and the air rushing by cools the wire. The car’s computer is then programmed to inject fuel according to the estimated amount of air coming in, which is double checked with oxygen sensors in the exhaust (which detect uncombusted air, i.e., too little fuel).
I think it’s better to think about what swap is, and the right answer might well be zero. If you try to allocate memory and there isn’t any available, then existing stuff in memory is transferred to the swap file/partition. This is incredibly slow. If there isn’t enough memory or swap available, then at least one process (one hopes the one that made the unfulfillable request for memory) is killed.
If you ever do start swapping memory to disk, your computer will grind to a halt.
Maybe someone will disagree with me, and if someone does I’m curious why, but unless you’re in some sort of very high memory utilization situation, processes being killed is probably easier to deal with than the huge delays caused by swapping.
Edit: Didn’t notice what community this was. Since it’s a webserver, the answer requires some understanding of utilization. You might want to look into swap files rather than swap partitions, since I’m pretty sure they’re easier to resize as conditions change.