BUG#22178: Scan ordered performed also on engines not supporting ordered scans

Scan of ranges without start key should not use ordered scans unless it
is requested.

sql/ha_partition.cc

@@ -3655,7 +3655,10 @@ int ha_partition::read_range_first(const key_range *start_key,
 
   if (!start_key)				// Read first record
   {
-    m_index_scan_type= partition_index_first;
+    if (m_ordered)
+      m_index_scan_type= partition_index_first;
+    else
+      m_index_scan_type= partition_index_first_unordered;
     error= common_first_last(m_rec0);
   }
   else
@@ -3869,6 +3872,18 @@ int ha_partition::handle_unordered_scan_next_partition(byte * buf)
       DBUG_PRINT("info", ("index_first on partition %d", i));
       error= file->index_first(buf);
       break;
+    case partition_index_first_unordered:
+      /*
+        We perform a scan without sorting and this means that we
+        should not use the index_first since not all handlers
+        support it and it is also unnecessary to restrict sort
+        order.
+      */
+      DBUG_PRINT("info", ("read_range_first on partition %d", i));
+      table->record[0]= buf;
+      error= file->read_range_first(0, end_range, eq_range, 0);
+      table->record[0]= m_rec0;
+      break;
     default:
       DBUG_ASSERT(FALSE);
       DBUG_RETURN(1);

sql/ha_partition.h

@@ -45,9 +45,10 @@ class ha_partition :public handler
   {
     partition_index_read= 0,
     partition_index_first= 1,
-    partition_index_last= 2,
-    partition_index_read_last= 3,
-    partition_no_index_scan= 4
+    partition_index_first_unordered= 2,
+    partition_index_last= 3,
+    partition_index_read_last= 4,
+    partition_no_index_scan= 5
   };
   /* Data for the partition handler */
   int  m_mode;                          // Open mode