refs #5375 fix column rename + update deadlock on the mainline * 5.5

git-svn-id: file:///svn/mysql/tokudb-engine/tokudb-engine@46890 c7de825b-a66e-492c-adef-691d508d4ae1

storage/tokudb/ha_tokudb_alter_56.cc

@@ -113,6 +113,16 @@ only_flags(ulong bits, ulong mask) {
     return (bits & mask) != 0 && (bits & ~mask) == 0;
 }
 
+// Check if an alter table operation on this table and described by the alter table parameters is supported inplace
+// and if so, what type of locking is needed to execute it.
+// return values:
+// HA_ALTER_INPLACE_NOT_SUPPORTED:  alter operation is not supported as an inplace operation, a table copy is required
+// HA_ALTER_ERROR: the alter table operation should fail
+// HA_ALTER_INPLACE_SHARED_LOCK: prepare and alter methods called with MDL SNW, concurrent reads, no writes
+// HA_ALTER_INPLACE_NO_LOCK: prepare and alter methods called with MDL SW, concurrent reads, writes.
+//                           must set WRITE_ALLOW_WRITE lock type in the external lock method to avoid deadlocks
+//                           with the MDL lock and the table lock
+// HA_ALTER_INPLACE_EXCLUSIVE_LOCK: the alter operation requires an exclusive MDL no concurrent reads, no writes
 enum_alter_inplace_result
 ha_tokudb::check_if_supported_inplace_alter(TABLE *altered_table, Alter_inplace_info *ha_alter_info) {
     TOKUDB_DBUG_ENTER("check_if_supported_alter");
@@ -145,13 +155,14 @@ ha_tokudb::check_if_supported_inplace_alter(TABLE *altered_table, Alter_inplace_
             // for now, hot indexing is only supported via session variable with the create index sql command
             if (ha_alter_info->index_add_count == 1 && ha_alter_info->index_drop_count == 0 && 
                 get_create_index_online(thd) && thd_sql_command(thd) == SQLCOM_CREATE_INDEX) {
+                // external_lock set WRITE_ALLOW_WRITE which allows writes concurrent with the index creation
                 result = HA_ALTER_INPLACE_NO_LOCK; 
             }
         }
     } else
     // column default
     if (only_flags(handler_flags, Alter_inplace_info::ALTER_COLUMN_DEFAULT)) {
-        result = HA_ALTER_INPLACE_NO_LOCK;
+        result = HA_ALTER_INPLACE_EXCLUSIVE_LOCK;
     } else
     // column rename
     if (only_flags(handler_flags, Alter_inplace_info::ALTER_COLUMN_NAME + Alter_inplace_info::ALTER_COLUMN_DEFAULT)) {
@@ -166,7 +177,7 @@ ha_tokudb::check_if_supported_inplace_alter(TABLE *altered_table, Alter_inplace_
         // the contrary, we don't allow it, also check indexes
         bool cr_supported = column_rename_supported(table, altered_table, (ha_alter_info->handler_flags & Alter_inplace_info::ALTER_COLUMN_ORDER) != 0);
         if (cr_supported)
-            result = HA_ALTER_INPLACE_NO_LOCK;
+            result = HA_ALTER_INPLACE_EXCLUSIVE_LOCK;
     } else    
     // add column
     if (only_flags(handler_flags, Alter_inplace_info::ADD_COLUMN + Alter_inplace_info::ALTER_COLUMN_ORDER)) {