It's not salting your water, nor the water volume to pasta ratio, nor if the water is boiling or not, nor oil in the water, but stirring early in the cooking process that will prevent sticking.
From the great Kenji Lopez-Alt:
Pasta is made up of flour, water, and sometimes eggs. Essentially, it's composed of starch and protein, and not much else. Now starch molecules come aggregated into large granules that resemble little water balloons. As they get heated in a moist environment, they absorb more and more water until they finally burst, releasing the starch molecules into the water. That's why pasta always seems to stick together at the beginning of cooking—it's the starch molecules coming out and acting as a sort of glue, binding the pieces to each other, and to the pot.
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The problem is that first stage of cooking—the one in which starch molecules first burst and release their starch. With such a high concentration of starch right on the surface of the pasta, sticking is inevitable. However, once the starch gets rinsed away in the water, the problem is completely gone.
So the key is to stir the pasta a few times during the critical first minute or two. After that, whether the pasta is swimming in a hot tub of water or just barely covered as it is here, absolutely no sticking occurs. I was able to clean this pot with a simple rinse.
