Richard is right. But I have another question. Wy do you wants to display 20000 pushpins ? Nobody can see or count them.
I should take another approach. Wy just display pushpins as needed ? For example limit them to 1000 or so (even less, 100 or 200). Nobody can click a pushpin if there are 1000 on the screen.
You have to design a algoritm to display the pushpins equally of course. Not just limit them.
Finally when a user zoom in then he has more resolution and can click on a pushpin.
My English is not good, but do I make sence what I try to say ?