Why are iframe uploads so slow?

Is there a reason server-side or 开发者_开发百科client-side why uploading even a tiny file via the iframe method can take such a long time?

I'm just trying to upload a file via an iframe so the user doesn't have to leave the page. It all works but it's incredibly slow. Oddly enough, one time in umpteen, it will actually go through quickly. I'm not sure what's going on.

Browser is Firefox 3.6. Server is CentOS 4 with HTTPd 2.0.

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My bad, turns out the code I got from elsewhere was submitting using the same form which in this case was very large. It made the browser compile everything for submission just for the upoad. And the server-side process had to decompile all of that on its end, too. Combined, I guess that's why it was slow.