varnish 4.0：

​ vcl_init

​ vcl_recv

​ vcl_hash

​ vcl_hit

​ vcl_pass

​ vcl_miss

​ vcl_pipe

​ vcl_waiting

​ vcl_purge

​ vcl_deliver

​ vcl_synth

​ vcl_fini

​

​ vcl_backend_fetch

​ vcl_backend_response

​ vcl_backend_error