One of the easiest way of increasing the responsiveness of your server and guarding against out of memory errors in your applications is to add some swap space. Swap is an area on a hard drive that has been designated as a place where the operating system can temporarily store data that it can no longer hold in RAM. The information written to disk will be slower than information kept in RAM, but the operating system will prefer to keep running application data in memory and use swap for the older data. Overall, having swap space as a fall back for when your system's RAM is depleted is a good safety net. In this guide, we'll cover how to create and enable a swap file on an Ubuntu 14.04 server.

https://www.digitalocean.com/community/tutorials/how-to-add-swap-on-ubuntu-14-04

Adding swap is only to be used to give your server a bit of breathing space.  If your server is constantly using a lot of swap memory consider upgrading the amount of RAM.