They're two distinct words. To "poll" is to ask for an answer. To "pull" is to use force to move (actually or conceptually) something towards oneself (again, actually or conceptually).
One "polls" a server when software on a client periodically asks the server for something. One "pulls" data from a database towards client software.
Note that both words have various distinct uses even within the world of computing, but I can't think of any case where they're interchangeable in such a way as to leave meaning unchanged. Low-level device driver code may "poll" an interface to check whether it's ready for some operation, and there's no network traffic involved. In electronics, one "pulls" a signal up or down.
Clients may both "poll" a server and "pull" data from a server, but note that when I use each verb I use different direct objects. It only makes sense to say "pull the server" when you're dragging it across the computer room floor.
与恶龙缠斗过久,自身亦成为恶龙；凝视深渊过久,深渊将回以凝视…
