what does ecf_LineItem_Update do in episerver?. Does it update it update price and Total price for the cart?
As a reminder Episerver does not disclose the database, and it is treated like blackbox.
ecf_LineItem_Update is used when you update a cart (not in serializable cart mode) or an order, when you make change for a line item, for example update the quantity.
Unfortunately no. The way the order system is designed requires one call per line item - in later versions if you only update one lineitem, only that one will be updated. If you are using the old cart system, you might consider moving to the serializable cart. there is no "serializable order" system, however