C: Client;
S: Server;
B: Backend;
->C: Hit;
mark top;
C==C: Generate\nrequest;
C=>S: Request;
note: This must\nbe very fast;
S..B: Server gets info
{
    S>>B: Query;
    S<<B: Response;
};
vertical brace at S- :Query;
C<=S: Reply;
vertical range top<-> at C-: Whole process;
