I intend to get the sequence number of next request in gdk-xcb, because gdk-x11 use the NextRequest macro. I see that the cookie returned by every request contains the sequence number of that request. But It is impossible to find the last request before I want the sequence number in such a event-driven system. So I use xcb_no_operation. Instead of NextRequest macro, I just write a XCBNextRequest macro in gdk-xcb :     #define XCBNextRequest(c)             ((xcb_no_operation(c)).sequence + 1) As a result gdk-xcb send the xcb_no_operation_request frequently when window redraw occurs. Maybe this brings down the gdk-xcb's performance? Should I avoid using xcb_no_operation? "This design choice causes XCBNoOperation to be something like a factor of four times slower than XNoOperation in the current implementation. Note that NoOperation, a completely useless request, suffers the most...", Jamey said (How XCB's design affects its performance, <a href="http://solair.livejournal.com">solair.livejournal.com</a>). Is it still right now? Thanks Jianjun