More session confusion

Ok, when you define your own session handler funcions, when you call the session_start() function it automatically calls your defined "open", "write" and "read" functions. Is this correct? The reason I am unclear is that in my "write" function, I have a query that updates/inserts-to my database. I am also echoing out a message indicating where I am. When I comment out the line that actually runs the query, no record is created with my session_start() call. When I uncomment that line, a record is created. However, there is no message being echoed from the "write" function but there is from the "open" and "read" function. Is it not, in fact, automatically running my "write" function? If not, why is it that me commenting (or not) that one line have the described effect? What's going on? Chris