Method dsmrr_init

sql/multi_range_read.cc:1124–1352

*/

int DsMrr_impl::dsmrr_init(handler *h_arg, RANGE_SEQ_IF *seq_funcs, 
                           void *seq_init_param, uint n_ranges, uint mode,
                           HANDLER_BUFFER *buf)
{
  TABLE *table= h_arg->get_table();
  THD *thd= table->in_use;
  int res;
  Key_parameters keypar;
  uint UNINIT_VAR(key_buff_elem_size); /* set/used when do_sort_keys==TRUE */
  handler *h_idx;
  Mrr_ordered_rndpos_reader *disk_strategy= NULL;
  bool do_sort_keys= FALSE;
  DBUG_ENTER("DsMrr_impl::dsmrr_init");
  /*
    index_merge may invoke a scan on an object for which dsmrr_info[_const]
    has not been called, so set the owner handler here as well.
  */
  primary_file= h_arg;
  is_mrr_assoc= !MY_TEST(mode & HA_MRR_NO_ASSOCIATION);

  strategy_exhausted= FALSE;
  
  /* By default, have do-nothing buffer manager */
  buf_manager.arg= this;
  buf_manager.reset_buffer_sizes= do_nothing;
  buf_manager.redistribute_buffer_space= do_nothing;

  if (!hint_key_state(thd, table, h_arg->active_index,
                MRR_HINT_ENUM, optimizer_flag(thd, OPTIMIZER_SWITCH_MRR)) ||
      mode & (HA_MRR_USE_DEFAULT_IMPL | HA_MRR_SORTED))
    goto use_default_impl;
  
  /*
    Determine whether we'll need to do key sorting and/or rnd_pos() scan
  */
  index_strategy= NULL;
  if ((mode & HA_MRR_SINGLE_POINT) &&
      optimizer_flag(thd, OPTIMIZER_SWITCH_MRR_SORT_KEYS))
  {
    do_sort_keys= TRUE;
    index_strategy= &reader_factory.ordered_index_reader;
  }
  else
    index_strategy= &reader_factory.simple_index_reader;

  strategy= index_strategy;
  /*
    We don't need a rowid-to-rndpos step if
     - We're doing a scan on clustered primary key
     - [In the future] We're doing an index_only read
  */
  DBUG_ASSERT(primary_file->inited == handler::INDEX || 
              (primary_file->inited == handler::RND && 
               secondary_file && 
               secondary_file->inited == handler::INDEX));

  h_idx= (primary_file->inited == handler::INDEX)? primary_file: secondary_file;
  keyno= h_idx->active_index;