MDEV-21610 Different query results from 10.4.11 to 10.4.12

Part#2: cleanup:

In the part 1 of the fix, DS-MRR implementation would peek into
the JOIN_TAB to get the rowid filter from

  table->reginfo.join_tab->rowid_filter

This doesn't look good from code isolation standpoint (why should a
storage engine assume it is used through a JOIN_TAB?).

Fixed this by storing the 'un-pushed' rowid_filter in the DsMrr_impl
structure. The filter survives across multi_range_read_init() calls.

It is discarded when somebody calls index_end() or rnd_end() and cleans
up the DsMrr_impl.

sql/multi_range_read.cc

@@ -1015,6 +1015,7 @@ int DsMrr_impl::dsmrr_init(handler *h_arg, RANGE_SEQ_IF *seq_funcs,
         primary key. Use the rowid filter outside the engine code (see
         Mrr_ordered_rndpos_reader::refill_from_index_reader).
       */
+      rowid_filter= h_arg->pushed_rowid_filter;
       h_arg->cancel_pushed_rowid_filter();
     }
   }
@@ -1096,15 +1097,18 @@ int DsMrr_impl::dsmrr_init(handler *h_arg, RANGE_SEQ_IF *seq_funcs,
         goto use_default_impl;
     }
 
+    // setup_two_handlers() will call dsmrr_close() will clears the filter.
+    // Save its value and restore afterwards.
+    Rowid_filter *tmp = rowid_filter;
     if ((res= setup_two_handlers()))
       goto error;
+    rowid_filter= tmp;
 
     if ((res= index_strategy->init(secondary_file, seq_funcs, seq_init_param,
                                    n_ranges, mode, &keypar, key_buffer, 
                                    &buf_manager)) || 
         (res= disk_strategy->init(primary_file, index_strategy, mode, 
-                                  &rowid_buffer,
-                                  table->reginfo.join_tab->rowid_filter)))
+                                  &rowid_buffer, rowid_filter)))
     {
       goto error;
     }
@@ -1286,6 +1290,7 @@ void DsMrr_impl::close_second_handler()
 void DsMrr_impl::dsmrr_close()
 {
   DBUG_ENTER("DsMrr_impl::dsmrr_close");
+  rowid_filter= NULL;
   close_second_handler();
   strategy= NULL;
   DBUG_VOID_RETURN;

sql/multi_range_read.h

@@ -557,7 +557,8 @@ class DsMrr_impl
   typedef void (handler::*range_check_toggle_func_t)(bool on);
 
   DsMrr_impl()
-    : secondary_file(NULL) {};
+    : secondary_file(NULL),
+      rowid_filter(NULL) {};
   
   void init(handler *h_arg, TABLE *table_arg)
   {
@@ -594,7 +595,13 @@ class DsMrr_impl
     to run both index scan and rnd_pos() scan at the same time)
   */
   handler *secondary_file;
-  
+
+  /*
+    The rowid filter that DS-MRR has "unpushed" from the storage engine.
+    If it's present, DS-MRR will use it.
+  */
+  Rowid_filter *rowid_filter;
+
   uint keyno; /* index we're running the scan on */
   /* TRUE <=> need range association, buffers hold {rowid, range_id} pairs */
   bool is_mrr_assoc;