Fix to #478, http://bugs.skysql.com/show_bug.cgi?id=478

Execution of session commands failed because session commands and normal sql statements were executed in a wrong order if backend was executing previous session command while new sql stmt was routed to that backend. There was a window where ordering went wrong.
It is possible that one normal sql stmt arrives while previous sescmds are still being executed.

Introduced a new member in backend_ref_t structure, bref_pending_cmd where new sql stmt pointer is stored in that case. When sescmds are executed completely, that command is automatically executed next.

server/core/dcb.c

@@ -485,7 +485,6 @@ bool    succp = false;
                 /*<
                  * Close file descriptor and move to clean-up phase.
                  */
-		ss_dassert(excluded != dcb);
                 rc = close(dcb->fd);
 
                 if (rc < 0) {

server/modules/include/readwritesplit.h

@@ -224,6 +224,7 @@ typedef struct backend_ref_st {
         bref_state_t    bref_state;
         int             bref_num_result_wait;
         sescmd_cursor_t bref_sescmd_cur;
+	GWBUF*          bref_pending_cmd; /*< For stmt which can't be routed due active sescmd execution */
 #if defined(SS_DEBUG)
         skygw_chk_t     bref_chk_tail;
 #endif

server/modules/protocol/mysql_common.c

@@ -1642,6 +1642,8 @@ void protocol_archive_srv_command(
         server_command_t*  h1;
         int                len = 0;
         
+	CHK_PROTOCOL(p);
+	
         spinlock_acquire(&p->protocol_lock);
         
         if (p->protocol_state != MYSQL_PROTOCOL_ACTIVE)
@@ -1692,6 +1694,7 @@ void protocol_archive_srv_command(
         
 retblock:
         spinlock_release(&p->protocol_lock);
+	CHK_PROTOCOL(p);
 }
 
 

server/modules/routing/readwritesplit/readwritesplit.c

@@ -1957,6 +1957,26 @@ static int routeQuery(
 	
 	if (succp) /*< Have DCB of the target backend */
 	{
+		backend_ref_t*   bref;
+		sescmd_cursor_t* scur;
+		
+		bref = get_bref_from_dcb(router_cli_ses, target_dcb);
+		scur = &bref->bref_sescmd_cur;
+		/** 
+		 * Store current stmt if execution of previous session command 
+		 * haven't completed yet. Note that according to MySQL protocol
+		 * there can only be one such non-sescmd stmt at the time.
+		 */
+		if (sescmd_cursor_is_active(scur))
+		{
+			ss_dassert(bref->bref_pending_cmd == NULL);
+			bref->bref_pending_cmd = gwbuf_clone(querybuf);
+			
+			rses_end_locked_router_action(router_cli_ses);
+			ret = 1;
+			goto retblock;
+		}
+			
 		if ((ret = target_dcb->func.write(target_dcb, gwbuf_clone(querybuf))) == 1)
 		{
 			backend_ref_t* bref;
@@ -2295,7 +2315,34 @@ static void clientReply (
                 
                 ss_dassert(succp);
         }
-        /** Unlock router session */
+	else if (bref->bref_pending_cmd != NULL) /*< non-sescmd is waiting to be routed */
+	{
+		int ret;
+		
+		CHK_GWBUF(bref->bref_pending_cmd);
+		
+		if ((ret = bref->bref_dcb->func.write(bref->bref_dcb, 
+			gwbuf_clone(bref->bref_pending_cmd))) == 1)
+		{
+			ROUTER_INSTANCE* inst = (ROUTER_INSTANCE *)instance;
+			atomic_add(&inst->stats.n_queries, 1);
+			/**
+			 * Add one query response waiter to backend reference
+			 */
+			bref_set_state(bref, BREF_QUERY_ACTIVE);
+			bref_set_state(bref, BREF_WAITING_RESULT);
+		}
+		else
+		{
+			LOGIF(LE, (skygw_log_write_flush(
+				LOGFILE_ERROR,
+				"Error : Routing query \"%s\" failed.",
+				bref->bref_pending_cmd)));
+		}
+		gwbuf_free(bref->bref_pending_cmd);
+		bref->bref_pending_cmd = NULL;
+	}
+	/** Unlock router session */
         rses_end_locked_router_action(router_cli_ses);
         
 lock_failed:
@@ -3656,6 +3703,14 @@ static bool route_session_write(
                                 {
                                         succp = false;
                                 }
+                                else if (LOG_IS_ENABLED(LOGFILE_TRACE))
+				{
+					LOGIF(LT, (skygw_log_write(
+						LOGFILE_TRACE,
+						"Wrote to %s:%d",
+						backend_ref[i].bref_backend->backend_server->name,
+						backend_ref[i].bref_backend->backend_server->port)));
+				}					
                         }
                 }
                 rses_end_locked_router_action(router_cli_ses);