I saw a sentence which doesn't have comma before which.
Here is the sentence:"That introduces essential clauses while which introduces nonessential clauses."
I think above sentence consists of two independent clauses combined by while like this
: "independent clause(That introduces.....) while independent clause(which+introduces....)"
But, doesn't this sentence need comma(,) in front of while? And does native speaker usually omit comma when combine two independent clauses?
However, to your question: I'd put a comma there, but it doesn't seem obligatory to me.
"That introduces essential clauses, while which introduces nonessential clauses."