What is swap partition? How is it important and what is the recommended size of in question partition?

In it’s simplest sense, the SWAP partition acts as an overflow to your (RAM) memory. If your memory is filled up completely, any additional applications will be run off of the SWAP partition rather than memory.

The size of the swap partition should be the size of your installed memory, plus an additional 10-25% to leave room for any items that were already moved over into the SWAP partition.

If the system needs more memory resources and the RAM is full, inactive pages in memory are moved to the swap space.swap space is maximum twice the amount of RAM