MDEV-11016 wsrep_node_is_ready() check is too strict

Problem:-
  The condition that checks for node readiness is too strict as it does
  not allow SELECTs even if these selects do not access any tables.
    For example,if we run
       SELECT 1;
    OR
       SELECT @@max_allowed_packet;
Solution:-
  We need not to report this error when all_tables(lex->query_tables)
  is NULL:

mysql-test/suite/galera/r/MW-284.result

@@ -2,12 +2,14 @@ CREATE TABLE t1 (f1 INTEGER) ENGINE=InnoDB;
 SET GLOBAL wsrep_provider_options='gmcast.isolate=1';
 SET SESSION wsrep_on = OFF;
 SET SESSION wsrep_on = ON;
+SET global wsrep_sync_wait=0;
 START SLAVE;
 include/wait_for_slave_param.inc [Slave_IO_Running]
 SET GLOBAL wsrep_provider_options='gmcast.isolate=0';
 include/wait_for_slave_to_start.inc
 INSERT INTO t1 VALUES (1);
 DROP TABLE t1;
+SET global wsrep_sync_wait=7;
 STOP SLAVE;
 RESET SLAVE ALL;
 CALL mtr.add_suppression('failed registering on master');

mysql-test/suite/galera/r/galera_var_dirty_reads.result

@@ -18,6 +18,15 @@ Variable_name	Value
 wsrep_cluster_status	non-Primary
 SELECT * FROM t1;
 ERROR 08S01: WSREP has not yet prepared node for application use
+SELECT @@wsrep_dirty_reads;
+@@wsrep_dirty_reads
+0
+SELECT 2;
+2
+2
+SELECT 2+2 FROM DUAL;
+2+2
+4
 SET @@session.wsrep_dirty_reads=ON;
 SELECT * FROM t1;
 i

mysql-test/suite/galera/t/MW-284.test

@@ -11,12 +11,16 @@
 --enable_query_log
 
 --connection node_1
+--let $wsrep_sync_wait_state= `SELECT @@global.wsrep_sync_wait;`
 CREATE TABLE t1 (f1 INTEGER) ENGINE=InnoDB;
 SET GLOBAL wsrep_provider_options='gmcast.isolate=1';
 SET SESSION wsrep_on = OFF;
 --let $wait_condition = SELECT VARIABLE_VALUE = 'non-Primary' FROM INFORMATION_SCHEMA.GLOBAL_STATUS WHERE VARIABLE_NAME = 'wsrep_cluster_status'
 --source include/wait_condition.inc
 SET SESSION wsrep_on = ON;
+#wsrep_sync_wait is set to zero because when slave tries to connect it it ask for queries like SELECT UNIX_TIMESTAMP() on node 1 which will fail, causing
+#a warning in slave error log.
+SET global wsrep_sync_wait=0;
 
 --connection node_3
 START SLAVE;
@@ -47,6 +51,7 @@ INSERT INTO t1 VALUES (1);
 --connection node_1
 DROP TABLE t1;
 
+--eval SET global wsrep_sync_wait=$wsrep_sync_wait_state
 --connection node_3
 --let $wait_condition = SELECT COUNT(*) = 0 FROM INFORMATION_SCHEMA.TABLES WHERE TABLE_NAME = 't1'
 --source include/wait_condition.inc

mysql-test/suite/galera/t/galera_var_dirty_reads.test

@@ -37,6 +37,11 @@ SHOW STATUS LIKE 'wsrep_cluster_status';
 --error ER_UNKNOWN_COM_ERROR
 SELECT * FROM t1;
 
+#Select query which does not access table should be allowed MDEV-11016
+SELECT @@wsrep_dirty_reads;
+SELECT 2;
+SELECT 2+2 FROM DUAL;
+
 SET @@session.wsrep_dirty_reads=ON;
 
 SELECT * FROM t1;

sql/sql_parse.cc

@@ -288,6 +288,7 @@ void init_update_queries(void)
   server_command_flags[COM_STMT_RESET]= CF_SKIP_QUESTIONS | CF_SKIP_WSREP_CHECK;
   server_command_flags[COM_STMT_EXECUTE]= CF_SKIP_WSREP_CHECK;
   server_command_flags[COM_STMT_SEND_LONG_DATA]= CF_SKIP_WSREP_CHECK;
+  server_command_flags[COM_REGISTER_SLAVE]= CF_SKIP_WSREP_CHECK;
 
   /* Initialize the sql command flags array. */
   memset(sql_command_flags, 0, sizeof(sql_command_flags));
@@ -2651,7 +2652,7 @@ mysql_execute_command(THD *thd)
     /*
       Bail out if DB snapshot has not been installed. SET and SHOW commands,
       however, are always allowed.
-
+      Select query is also allowed if it does not access any table.
       We additionally allow all other commands that do not change data in
       case wsrep_dirty_reads is enabled.
     */
@@ -2659,6 +2660,8 @@ mysql_execute_command(THD *thd)
         !wsrep_is_show_query(lex->sql_command) &&
         !(thd->variables.wsrep_dirty_reads     &&
           !is_update_query(lex->sql_command))  &&
+        !(lex->sql_command == SQLCOM_SELECT    &&
+          !all_tables)                         &&
         !wsrep_node_is_ready(thd))
       goto error;
   }