What effect does framerate have on mob spawning?

Prior to 1.6 I had set the video option "limit framerate" when trying to eliminate a persistent hang problem (which finally went away when I dropped my view distance from "far" to "normal"). I also built a large (80x30) mob spawner that could go 8+ hours with nothing spawning inside. In fact, often when the mob spawner would dry up I could wander through caves for hours and never have any monsters spawn at all. With "F3 radar" I could see that nothing was spawning anywhere around me. I suspected a bug.

In 1.6 Notch un-limited anyone who had previously limited the framerate. Since it didn't matter I left it unlimited. Now my mob trap spawns mobs. And my typical framerate is only about 3x what the "limited" framerate was, so it's not linear.

I was wrong. I had one good session in the trap (4 or 5 stacks of gunpowder in a few hours) but I parked there overnight and got absolutely zero items.

Solution 1:

I know this is an old question, but it came up in a Google.

It has recently been theorised (and to a certain extent proved) that there is a bug related to mobs spawning on the edge of the loaded chunk area, wandering out and still using up the mob limit.

Further analysis and experimentation is available in this video.

Solution 2:

There is no effect as far as I know. All you need is light.