MDEV-37857 : Galera replication does not preserve the character set and collation associated with views, etc

In Query_log_event::do_apply_event there is comparison is used
character set in event same as cached charset and if not used
charset is changed. Unfortunately, it was done only if thread is
replica thread.

Fixed by adding condition for Galera applier thread so that
comparison is done leading to charset change if event
had different charset.

Author: janlindstrom

mysql-test/suite/galera/r/MDEV-37857.result

@@ -0,0 +1,44 @@
+connection node_2;
+connection node_1;
+drop table if exists t1;
+drop view if exists t1;
+connection node_2;
+SELECT @@character_set_server, @@collation_server;
+@@character_set_server	@@collation_server
+latin1	latin1_swedish_ci
+SELECT @@character_set_client, @@collation_connection;
+@@character_set_client	@@collation_connection
+latin1	latin1_swedish_ci
+connection node_1;
+SET NAMES latin1 COLLATE latin1_bin;
+SELECT @@character_set_server, @@collation_server;
+@@character_set_server	@@collation_server
+latin1	latin1_swedish_ci
+SELECT @@character_set_client, @@collation_connection;
+@@character_set_client	@@collation_connection
+latin1	latin1_bin
+create table t1 (a int);
+insert into t1 values (1);
+create view v1 as select a from t1;
+SHOW CREATE VIEW v1;
+View	Create View	character_set_client	collation_connection
+v1	CREATE ALGORITHM=UNDEFINED DEFINER=`root`@`localhost` SQL SECURITY DEFINER VIEW `v1` AS select `t1`.`a` AS `a` from `t1`	latin1	latin1_bin
+SHOW CREATE TABLE t1;
+Table	Create Table
+t1	CREATE TABLE `t1` (
+  `a` int(11) DEFAULT NULL
+) ENGINE=InnoDB DEFAULT CHARSET=latin1 COLLATE=latin1_swedish_ci
+connection node_2;
+SHOW CREATE VIEW v1;
+View	Create View	character_set_client	collation_connection
+v1	CREATE ALGORITHM=UNDEFINED DEFINER=`root`@`localhost` SQL SECURITY DEFINER VIEW `v1` AS select `t1`.`a` AS `a` from `t1`	latin1	latin1_bin
+SHOW CREATE TABLE t1;
+Table	Create Table
+t1	CREATE TABLE `t1` (
+  `a` int(11) DEFAULT NULL
+) ENGINE=InnoDB DEFAULT CHARSET=latin1 COLLATE=latin1_swedish_ci
+connection node_1;
+DROP VIEW v1;
+DROP TABLE t1;
+disconnect node_2;
+disconnect node_1;

mysql-test/suite/galera/t/MDEV-37857.test

@@ -0,0 +1,29 @@
+--source include/galera_cluster.inc
+
+--disable_warnings
+drop table if exists t1;
+drop view if exists t1;
+--enable_warnings
+
+--connection node_2
+SELECT @@character_set_server, @@collation_server;
+SELECT @@character_set_client, @@collation_connection;
+--connection node_1
+SET NAMES latin1 COLLATE latin1_bin;
+SELECT @@character_set_server, @@collation_server;
+SELECT @@character_set_client, @@collation_connection;
+create table t1 (a int);
+insert into t1 values (1);
+create view v1 as select a from t1;
+SHOW CREATE VIEW v1;
+SHOW CREATE TABLE t1;
+
+--connection node_2
+SHOW CREATE VIEW v1;
+SHOW CREATE TABLE t1;
+
+--connection node_1
+DROP VIEW v1;
+DROP TABLE t1;
+
+--source include/galera_end.inc

sql/log_event_server.cc

@@ -2021,7 +2021,16 @@ int Query_log_event::do_apply_event(rpl_group_info *rgi,
       if (charset_inited)
       {
         rpl_sql_thread_info *sql_info= thd->system_thread_info.rpl_sql_info;
-        if (thd->slave_thread && sql_info->cached_charset_compare(charset))
+        const bool applier=
+#ifdef WITH_WSREP
+          WSREP(thd) ? thd->wsrep_applier :
+#endif
+          false;
+
+        // Event charset should be compared for slave thread
+        // and applier threads
+        if ((thd->slave_thread || applier) &&
+	    sql_info->cached_charset_compare(charset))
         {
           /* Verify that we support the charsets found in the event. */
           if (!(thd->variables.character_set_client=