MDEV-18848 : Galera: 10.4 node crashed with Assertion...

MDEV-18848 : Galera: 10.4 node crashed with Assertion `client_state.transaction().active()` after altering SEQUENCE table's engine to myisam and back to innodb

We need to start Galera transaction for select NEXT VALUE FOR
sequence if it is not yet started. Note that ALTER is handled
as TOI and transaction is already started.

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

@@ -25,3 +25,25 @@ ERROR 42S02: Table 'test.seq' doesn't exist
 connection node_2;
 SHOW CREATE SEQUENCE seq;
 ERROR 42S02: Table 'test.seq' doesn't exist
+connection node_1;
+CREATE SEQUENCE Seq1_1     START WITH 1     INCREMENT BY 1;
+select NEXT VALUE FOR Seq1_1;
+NEXT VALUE FOR Seq1_1
+1
+alter table Seq1_1 engine=myisam;
+select NEXT VALUE FOR Seq1_1;
+NEXT VALUE FOR Seq1_1
+1001
+alter table Seq1_1 engine=innodb;
+select NEXT VALUE FOR Seq1_1;
+NEXT VALUE FOR Seq1_1
+2001
+connection node_2;
+SHOW CREATE SEQUENCE Seq1_1;
+Table	Create Table
+Seq1_1	CREATE SEQUENCE `Seq1_1` start with 1 minvalue 1 maxvalue 9223372036854775806 increment by 1 cache 1000 nocycle ENGINE=InnoDB
+select NEXT VALUE FOR Seq1_1;
+NEXT VALUE FOR Seq1_1
+1
+connection node_1;
+DROP SEQUENCE Seq1_1;

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

 --source include/galera_cluster.inc
 
+#
+# MDEV-19353 : Alter Sequence do not replicate to another nodes with in Galera Cluster
+#
+
 --connection node_1
 CREATE SEQUENCE `seq` start with 1 minvalue 1 maxvalue 1000000 increment by 0 cache 1000 nocycle ENGINE=InnoDB;
 SHOW CREATE SEQUENCE seq;
@@ -22,3 +26,21 @@ SHOW CREATE SEQUENCE seq;
 --connection node_2
 --error ER_NO_SUCH_TABLE
 SHOW CREATE SEQUENCE seq;
+
+#
+# MDEV-18848 : Galera: 10.4 node crashed with Assertion `client_state.transaction().active()` after altering SEQUENCE table's engine to myisam and back to innodb
+#
+--connection node_1
+CREATE SEQUENCE Seq1_1     START WITH 1     INCREMENT BY 1;
+select NEXT VALUE FOR Seq1_1;
+alter table Seq1_1 engine=myisam;
+select NEXT VALUE FOR Seq1_1;
+alter table Seq1_1 engine=innodb;
+select NEXT VALUE FOR Seq1_1;
+
+--connection node_2
+SHOW CREATE SEQUENCE Seq1_1;
+select NEXT VALUE FOR Seq1_1;
+
+--connection node_1
+DROP SEQUENCE Seq1_1;

sql/ha_sequence.cc

@@ -30,6 +30,10 @@
 #include "sql_base.h"
 #include "log_event.h"
 
+#ifdef WITH_WSREP
+#include "wsrep_trans_observer.h" /* wsrep_start_transaction() */
+#endif
+
 /*
   Table flags we should inherit and disable from the original engine.
   We add HA_STATS_RECORDS_IS_EXACT as ha_sequence::info() will ensure
@@ -199,6 +203,7 @@ int ha_sequence::write_row(const uchar *buf)
   int error;
   sequence_definition tmp_seq;
   bool sequence_locked;
+  THD *thd= table->in_use;
   DBUG_ENTER("ha_sequence::write_row");
   DBUG_ASSERT(table->record[0] == buf);
 
@@ -235,8 +240,6 @@ int ha_sequence::write_row(const uchar *buf)
         on master and slaves
       - Check that the new row is an accurate SEQUENCE object
     */
-
-    THD *thd= table->in_use;
     if (table->s->tmp_table == NO_TMP_TABLE &&
         thd->mdl_context.upgrade_shared_lock(table->mdl_ticket,
                                              MDL_EXCLUSIVE,
@@ -255,6 +258,16 @@ int ha_sequence::write_row(const uchar *buf)
     sequence->write_lock(table);
   }
 
+#ifdef WITH_WSREP
+  /* We need to start Galera transaction for select NEXT VALUE FOR
+  sequence if it is not yet started. Note that ALTER is handled
+  as TOI. */
+  if (WSREP_ON && WSREP(thd) &&
+      !thd->wsrep_trx().active() &&
+      wsrep_thd_is_local(thd))
+    wsrep_start_transaction(thd, thd->wsrep_next_trx_id());
+#endif
+
   if (likely(!(error= file->update_first_row(buf))))
   {
     Log_func *log_func= Write_rows_log_event::binlog_row_logging_function;