MDEV-7122: Assertion `0' failed in subselect_hash_sj_engine::init

Fix test failure when using maria small-block size. We need to query
the max_key_length and max_key_parts based on the the tmp table engine.

sql/opt_subselect.cc

@@ -873,7 +873,8 @@ bool subquery_types_allow_materialization(Item_in_subselect *in_subs)
      See MDEV-7122. This check is performed inside create_tmp_table also and
      we must do it so that we know the table has keys created.
   */
-  if (total_key_length > HA_MAX_KEY_LENGTH || elements > HA_MAX_KEY_SEG)
+  if (total_key_length > tmp_table_max_key_length() ||
+      elements > tmp_table_max_key_parts())
     DBUG_RETURN(FALSE);
 
   in_subs->types_allow_materialization= TRUE;

sql/sql_select.cc

@@ -15307,13 +15307,6 @@ create_tmp_table(THD *thd, TMP_TABLE_PARAM *param, List<Item> &fields,
   if (!table->file)
     goto err;
 
-  /*
-    Temporary table storage engines must allow keys of at least
-    HA_MAX_KEY_LENGT and at least HA_MAX_KEY_SEG key parts.
-  */
-  DBUG_ASSERT(table->file->max_key_length() >= HA_MAX_KEY_LENGTH &&
-              table->file->max_key_parts() >= HA_MAX_KEY_SEG);
-
   if (!using_unique_constraint)
     reclength+= group_null_items;	// null flag is stored separately
 
@@ -16305,12 +16298,6 @@ create_internal_tmp_table_from_heap2(THD *thd, TABLE *table,
   if (!(new_table.file= get_new_handler(&share, &new_table.mem_root,
                                         new_table.s->db_type())))
     DBUG_RETURN(1);				// End of memory
-  /*
-    Temporary table storage engines must allow keys of at least
-    HA_MAX_KEY_LENGTH and at least HA_MAX_KEY_SEG key parts.
-  */
-  DBUG_ASSERT(new_table.file->max_key_length() >= HA_MAX_KEY_LENGTH &&
-              new_table.file->max_key_parts() >= HA_MAX_KEY_SEG);
 
   save_proc_info=thd->proc_info;
   thd_proc_info(thd, proc_info);

sql/sql_select.h

@@ -40,8 +40,21 @@
 #endif
 #if defined(USE_ARIA_FOR_TMP_TABLES)
 #define TMP_ENGINE_HTON maria_hton
+inline uint tmp_table_max_key_length() {
+  return maria_max_key_length();
+}
+
+inline uint tmp_table_max_key_parts() {
+  return maria_max_key_segments();
+}
 #else
 #define TMP_ENGINE_HTON myisam_hton
+inline uint tmp_table_max_key_length() {
+  return MI_MAX_KEY_LENGTH;
+}
+inline uint tmp_table_max_key_parts() {
+  return MI_MAX_KEY_SEG;
+}
 #endif
 /* Values in optimize */
 #define KEY_OPTIMIZE_EXISTS		1