Method check_for_splittable_materialized

sql/opt_split.cc:404–598

*/

bool JOIN::check_for_splittable_materialized()
{
  ORDER *partition_list= 0;
  st_select_lex_unit *unit= select_lex->master_unit();
  TABLE_LIST *derived= unit->derived;

  hint_state hint;
  if (!is_split_materialized_allowed(thd, derived, &hint) ||          // !(1)
      !derived->is_materialized_derived() ||                          // !(2)
      (unit->first_select()->next_select()) ||                        // !(3)
      (derived->prohibit_cond_pushdown) ||                            // !(4)
      (derived->is_recursive_with_table()) ||                         // !(5)
      (table_count == 0 || const_tables == top_join_tab_count) ||     // !(6)
      rollup.state != ROLLUP::STATE_NONE)                             // (10)
    return false;
  if (group_list)                                                     // (7.1)
  {
    if (!select_lex->have_window_funcs())
      partition_list= group_list;
  }
  else if (select_lex->have_window_funcs() &&
           select_lex->window_specs.elements == 1)                    // (7.2)
  {
    partition_list=
      select_lex->window_specs.head()->partition_list->first;
  }
  if (!partition_list)
    return false;

  if (select_lex->order_list.elements > 0 && !unit->lim.is_unlimited()) //!(11)
    return false;

  Json_writer_object trace_wrapper(thd);
  Json_writer_object trace_split(thd, "check_split_materialized");

  ORDER *ord;
  Dynamic_array<SplM_field_ext_info> candidates(PSI_INSTRUMENT_MEM);

  /*
    Select from partition_list all candidates for splitting.
    A candidate must be
    - field item or refer to such (8.1)
    - item mentioned in the select list (8.2)
    Put info about such candidates into the array candidates
  */
  table_map usable_tables= 0;  // tables that contains the candidate
  for (ord= partition_list; ord; ord= ord->next)
  {
    Item *ord_item= *ord->item;
    if (ord_item->real_item()->type() != Item::FIELD_ITEM)   // !(8.1)
      continue;

    Field *ord_field= ((Item_field *) (ord_item->real_item()))->field;

    /* Ignore fields from  of inner tables of outer joins */
    TABLE_LIST *tbl= ord_field->table->pos_in_table_list;
    if (tbl->is_inner_table_of_outer_join())
      continue;