Method init_cache

sql/sql_cache.cc:2591–2767

size_t Query_cache::init_cache()
{
  size_t mem_bin_count, num, step;
  size_t mem_bin_size, prev_size, inc;
  size_t max_mem_bin_size, approx_additional_data_size;
  int align;

  DBUG_ENTER("Query_cache::init_cache");

  approx_additional_data_size = (sizeof(Query_cache) +
				 sizeof(uchar*)*(def_query_hash_size+
					       def_table_hash_size));
  if (query_cache_size < approx_additional_data_size)
    goto err;

  query_cache_size-= approx_additional_data_size;
  align= query_cache_size % ALIGN_SIZE(1);
  if (align)
  {
    query_cache_size-= align;
    approx_additional_data_size+= align;
  }

  /*
    Count memory bins number.
    Check section 6. in start comment for the used algorithm.
  */

  max_mem_bin_size = query_cache_size >> QUERY_CACHE_MEM_BIN_FIRST_STEP_PWR2;
  mem_bin_count = (uint)  ((1 + QUERY_CACHE_MEM_BIN_PARTS_INC) *
			   QUERY_CACHE_MEM_BIN_PARTS_MUL);
  mem_bin_num = 1;
  mem_bin_steps = 1;
  mem_bin_size = max_mem_bin_size >> QUERY_CACHE_MEM_BIN_STEP_PWR2;
  prev_size = 0;
  if (mem_bin_size <= min_allocation_unit)
  {
    DBUG_PRINT("qcache", ("too small query cache => query cache disabled"));
    // TODO here (and above) should be warning in 4.1
    goto err;
  }
  while (mem_bin_size > min_allocation_unit)
  {
    mem_bin_num += mem_bin_count;
    prev_size = mem_bin_size;
    mem_bin_size >>= QUERY_CACHE_MEM_BIN_STEP_PWR2;
    mem_bin_steps++;
    mem_bin_count += QUERY_CACHE_MEM_BIN_PARTS_INC;
    mem_bin_count = (uint) (mem_bin_count * QUERY_CACHE_MEM_BIN_PARTS_MUL);

    // Prevent too small bins spacing
    if (mem_bin_count > (mem_bin_size >> QUERY_CACHE_MEM_BIN_SPC_LIM_PWR2))
      mem_bin_count= (mem_bin_size >> QUERY_CACHE_MEM_BIN_SPC_LIM_PWR2);
  }
  inc = (prev_size - mem_bin_size) / mem_bin_count;
  mem_bin_num += (mem_bin_count - (min_allocation_unit - mem_bin_size)/inc);
  mem_bin_steps++;
  additional_data_size = ((mem_bin_num+1) *