Use reverse/backwards buffer for keys (now works)

- don't allocate space for rowid buffer when we don't really need it.
- fix buffer iterator

mysql-test/r/join_outer_jcl6.result

@@ -352,14 +352,14 @@ Thimble Smith	Happy	3	3
 Lilliana Angelovska	NULL	NULL	NULL
 select t1.name, t2.name, t2.id,t3.id from t1 right join t2 on (t1.id = t2.owner) right join t1 as t3 on t3.id=t2.owner;
 name	name	id	id
-Antonio Paz	El Gato	1	1
 Antonio Paz	Perrito	2	1
+Antonio Paz	El Gato	1	1
 Thimble Smith	Happy	3	3
 NULL	NULL	NULL	2
 select t1.name, t2.name, t2.id, t2.owner, t3.id from t1 left join t2 on (t1.id = t2.owner) right join t1 as t3 on t3.id=t2.owner;
 name	name	id	owner	id
-Antonio Paz	El Gato	1	1	1
 Antonio Paz	Perrito	2	1	1
+Antonio Paz	El Gato	1	1	1
 Thimble Smith	Happy	3	3	3
 NULL	NULL	NULL	NULL	2
 drop table t1,t2;
@@ -413,9 +413,9 @@ insert into t2 values (1, 2, 3),(2, 2, 8), (4,3,9),(3,2,10);
 select t1.*, t2.* from t1 left join t2 on t1.n = t2.n and
 t1.m = t2.m where t1.n = 1;
 n	m	o	n	m	o
-1	2	11	1	2	3
-1	2	7	1	2	3
 1	2	9	1	2	3
+1	2	7	1	2	3
+1	2	11	1	2	3
 1	3	9	NULL	NULL	NULL
 select t1.*, t2.* from t1 left join t2 on t1.n = t2.n and
 t1.m = t2.m where t1.n = 1 order by t1.o;

sql/multi_range_read.cc

@@ -420,7 +420,8 @@ int DsMrr_impl::dsmrr_init(handler *h_arg, RANGE_SEQ_IF *seq_funcs,
   }
 
   do_rowid_fetch= FALSE;
-  doing_cpk_scan= check_cpk_scan(h->active_index, mode);
+  doing_cpk_scan= check_cpk_scan(h->inited == handler::INDEX? 
+                                 h->active_index: h2->active_index, mode);
   if (!doing_cpk_scan /* && !index_only_read */)
   {
     /* Will use rowid buffer to store/sort rowids, etc */
@@ -754,7 +755,21 @@ void DsMrr_impl::setup_buffer_sizes(key_range *sample_key)
                                        key_tuple_length;
   key_buff_elem_size= key_size_in_keybuf + 
                       (int)is_mrr_assoc * sizeof(void*);
+  
+  if (!do_rowid_fetch)
+  {
+    /* Give all space to key buffer. */
+    key_buffer.set_buffer_space(full_buf, full_buf_end, 1);
 
+    /* Just in case, tell rowid buffer that it has zero size: */
+    rowid_buffer.set_buffer_space(full_buf_end, full_buf_end, 1);
+    return;
+  }
+  
+  /* 
+    Ok if we got here we need to allocate one part of the buffer 
+    for keys and another part for rowids.
+  */
   uint rowid_buf_elem_size= h->ref_length + 
                             (int)is_mrr_assoc * sizeof(char*);
   
@@ -790,9 +805,11 @@ void DsMrr_impl::setup_buffer_sizes(key_range *sample_key)
                 (h->ref_length + (int)is_mrr_assoc * sizeof(char*) + 1));
   }
 
+  //rowid_buffer.set_buffer_space(full_buf, full_buf + bytes_for_rowids, 1);
+  //key_buffer.set_buffer_space(full_buf + bytes_for_rowids, full_buf_end, 1);
   rowid_buffer.set_buffer_space(full_buf, full_buf + bytes_for_rowids, 1);
-  key_buffer.set_buffer_space(full_buf + bytes_for_rowids, full_buf_end, 1);
-
+  key_buffer.set_buffer_space(full_buf + bytes_for_rowids, full_buf_end, -1);
+  
   index_ranges_unique= test(key_info->flags & HA_NOSAME && 
                             key_info->key_parts == 
                               my_count_bits(sample_key->keypart_map));

sql/multi_range_read.h

@@ -118,7 +118,7 @@ public:
       }
       else
       {
-        if (pos - nbytes <= sb->write_pos)
+        if (pos - nbytes < sb->write_pos)
           return NULL;
         pos -= nbytes;
         return pos;