Bug #21378 Alter table from X storage engine to NDB could cause data loss: Added warning if local table shadows ndb table

mysql-test/r/ndb_multi.result

@@ -69,3 +69,35 @@ t3
 t4
 drop table t1, t2, t3, t4;
 drop table t1, t3, t4;
+create table t1(c1 int key)ENGINE=MyISAM;
+insert into t1 values(1),(3),(5);
+select * from t1 order by c1;
+c1
+1
+3
+5
+create table t1(c1 int key)ENGINE=MyISAM;
+insert into t1 values(100),(344),(533);
+select * from t1 order by c1;
+c1
+100
+344
+533
+alter table t1 engine=ndb;
+show tables;
+Tables_in_test
+t1
+Warnings:
+Warning	1050	Local table t1 shadows cluster table
+select * from t1 order by c1;
+c1
+100
+344
+533
+drop table t1;
+select * from t1 order by c1;
+c1
+1
+3
+5
+drop table t1;

mysql-test/t/ndb_multi.test

@@ -69,4 +69,26 @@ drop table t1, t2, t3, t4;
 connection server2;
 drop table t1, t3, t4;
 
+# bug#21378
+connection server1;
+create table t1(c1 int key)ENGINE=MyISAM;
+insert into t1 values(1),(3),(5);
+select * from t1 order by c1;
+
+connection server2;
+create table t1(c1 int key)ENGINE=MyISAM;
+insert into t1 values(100),(344),(533);
+select * from t1 order by c1;
+
+connection server1;
+alter table t1 engine=ndb;
+
+connection server2;
+show tables;
+select * from t1 order by c1;
+drop table t1;
+
+connection server1;
+select * from t1 order by c1;
+drop table t1;
 # End of 4.1 tests

sql/ha_ndbcluster.cc

@@ -4715,16 +4715,16 @@ int ndbcluster_find_files(THD *thd,const char *db,const char *path,
   List<char> delete_list;
   while ((file_name=it++))
   {
+    bool file_on_disk= false;
     DBUG_PRINT("info", ("%s", file_name));     
     if (hash_search(&ndb_tables, file_name, strlen(file_name)))
     {
       DBUG_PRINT("info", ("%s existed in NDB _and_ on disk ", file_name));
       // File existed in NDB and as frm file, put in ok_tables list
-      my_hash_insert(&ok_tables, (byte*)file_name);
-      continue;
+      file_on_disk= true;
     }
     
-    // File is not in NDB, check for .ndb file with this name
+    // Check for .ndb file with this name
     (void)strxnmov(name, FN_REFLEN, 
 		   mysql_data_home,"/",db,"/",file_name,ha_ndb_ext,NullS);
     DBUG_PRINT("info", ("Check access for %s", name));
@@ -4732,9 +4732,18 @@ int ndbcluster_find_files(THD *thd,const char *db,const char *path,
     {
       DBUG_PRINT("info", ("%s did not exist on disk", name));     
       // .ndb file did not exist on disk, another table type
+      if (file_on_disk)
+	push_warning_printf(current_thd, MYSQL_ERROR::WARN_LEVEL_WARN,
+			    ER_TABLE_EXISTS_ERROR,
+			    "Local table %s.%s shadows ndb table",
+			    db, file_name);
+      continue;
+    }
+    if (file_on_disk) 
+    {
+      my_hash_insert(&ok_tables, (byte*)file_name);
       continue;
     }
-
     DBUG_PRINT("info", ("%s existed on disk", name));     
     // The .ndb file exists on disk, but it's not in list of tables in ndb
     // Verify that handler agrees table is gone.