Fix debug assert on reconnection with session commands

When a query was routed to a server that must first be connected to, the
expected response count was not updated for the executed session commands.

server/core/backend.cc

@@ -96,6 +96,7 @@ bool Backend::execute_session_command()
     {
     case MXS_COM_QUIT:
     case MXS_COM_STMT_CLOSE:
+    case MXS_COM_STMT_SEND_LONG_DATA:
         /** These commands do not generate responses */
         rval = write(buffer, NO_RESPONSE);
         complete_session_command();

server/modules/routing/readwritesplit/rwbackend.hh

@@ -92,7 +92,7 @@ public:
      */
     bool continue_write(GWBUF* buffer)
     {
-        return mxs::Backend::write(buffer);
+        return mxs::Backend::write(buffer, Backend::NO_RESPONSE);
     }
 
     void close(close_type type = CLOSE_NORMAL);

server/modules/routing/readwritesplit/rwsplit_route_stmt.cc

@@ -117,6 +117,15 @@ bool RWSplitSession::prepare_target(SRWBackend& target, route_target_t route_tar
         ss_dassert(target->can_connect() && can_recover_servers());
         ss_dassert(!TARGET_IS_MASTER(route_target) || m_config.master_reconnection);
         rval = target->connect(m_client->session, &m_sescmd_list);
+        MXS_INFO("Connected to '%s'", target->name());
+
+        if (rval && target->is_waiting_result())
+        {
+            ss_info_dassert(!m_sescmd_list.empty() && target->has_session_commands(),
+                            "Session command list must not be empty and target "
+                            "should have unfinished session commands.");
+            m_expected_responses++;
+        }
     }
 
     return rval;
@@ -403,10 +412,6 @@ bool RWSplitSession::route_session_write(GWBUF *querybuf, uint8_t command, uint3
                 {
                     m_expected_responses++;
                 }
-                else
-                {
-                    backend->ack_write();
-                }
 
                 MXS_INFO("Route query to %s: %s \t%s",
                          backend->is_master() ? "master" : "slave",
@@ -1028,11 +1033,6 @@ bool RWSplitSession::handle_got_target(GWBUF* querybuf, SRWBackend& target, bool
                     m_qc.set_load_data_state(QueryClassifier::LOAD_DATA_INACTIVE);
                 }
             }
-            else
-            {
-                // The server won't respond, mark it as done
-                target->ack_write();
-            }
         }
 
         m_qc.set_large_query(large_query);

server/modules/routing/readwritesplit/rwsplitsession.cc

@@ -553,7 +553,7 @@ void RWSplitSession::clientReply(GWBUF *writebuf, DCB *backend_dcb)
 
     if (backend->has_session_commands())
     {
-        if (backend->execute_session_command())
+        if (backend->execute_session_command() && backend->is_waiting_result())
         {
             m_expected_responses++;
         }