Method setup_buffer_sharing

sql/multi_range_read.cc:1527–1576

*/

bool DsMrr_impl::setup_buffer_sharing(uint key_size_in_keybuf, 
                                      key_part_map key_tuple_map)
{
  long key_buff_elem_size= key_size_in_keybuf + 
                           (int)is_mrr_assoc * sizeof(range_id_t);
  
  KEY *key_info= &primary_file->get_table()->key_info[keyno];
  /* 
    Ok if we got here we need to allocate one part of the buffer 
    for keys and another part for rowids.
  */
  ulonglong rowid_buf_elem_size= primary_file->ref_length + 
                                 (int)is_mrr_assoc * sizeof(range_id_t);
  
  /*
    Use rec_per_key statistics as a basis to find out how many rowids 
    we'll get for each key value.
     TODO: what should be the default value to use when there is no 
           statistics?
  */
  uint parts= my_count_bits(key_tuple_map);
  ha_rows rpc;
  ulonglong rowids_size= rowid_buf_elem_size;
  if ((rpc= (ha_rows) key_info->actual_rec_per_key(parts - 1)))
    rowids_size= rowid_buf_elem_size * rpc;

  double fraction_for_rowids=
    (ulonglong2double(rowids_size) / 
     (ulonglong2double(rowids_size) + key_buff_elem_size));

  ptrdiff_t bytes_for_rowids= 
    (ptrdiff_t)floor(0.5 + fraction_for_rowids * (full_buf_end - full_buf));
  
  ptrdiff_t bytes_for_keys= (full_buf_end - full_buf) - bytes_for_rowids;

  if (bytes_for_keys < key_buff_elem_size + 1 ||
      bytes_for_rowids < (ptrdiff_t)rowid_buf_elem_size + 1)
    return TRUE; /* Failed to provide minimum space for one of the buffers */

  rowid_buffer_end= full_buf + bytes_for_rowids;
  rowid_buffer.set_buffer_space(full_buf, rowid_buffer_end);
  key_buffer= &backward_key_buf;
  key_buffer->set_buffer_space(rowid_buffer_end, full_buf_end); 

  /* The above code guarantees that the buffers are big enough */
  DBUG_ASSERT(key_buffer->have_space_for(key_buff_elem_size) &&
              rowid_buffer.have_space_for((size_t)rowid_buf_elem_size));

  return FALSE;
}


void DsMrr_impl::do_nothing(void *dsmrr_arg)