filesort.h

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   it under the terms of the GNU General Public License, version 2.0,
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   Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301  USA */
 
#ifndef FILESORT_INCLUDED
#define FILESORT_INCLUDED
 
#include <stddef.h>
#include <sys/types.h>
 
#include "mem_root_array.h"
#include "my_base.h" /* ha_rows */
#include "my_dbug.h"
#include "my_inttypes.h"
#include "my_table_map.h"
#include "sql/sort_param.h"
 
class Addon_fields;
class Field;
class JOIN;
class RowIterator;
class Sort_result;
class THD;
struct ORDER;
struct TABLE;
struct st_sort_field;
 
enum class Addon_fields_status;
 
/**
  Sorting related info.
*/
class Filesort {
 public:
  THD *m_thd;
  /// The tables we are sorting.
  Mem_root_array<TABLE *> tables;
  /// If true, do not free the filesort buffers (use if you expect to sort many
  /// times, like in an uncacheable subquery).
  const bool keep_buffers;
  /// Maximum number of rows to return
  ha_rows limit;
  /// ORDER BY list with some precalculated info for filesort
  st_sort_field *sortorder;
  /// true means we are using Priority Queue for order by with limit.
  bool using_pq;
  bool m_remove_duplicates;
  // If true, we will always sort references to rows on table (and crucially,
  // the result iterators used will always position the underlying table on
  // the original row before returning from Read()).
  bool m_force_sort_rowids;
  // TODO: Consider moving this into private members of Filesort.
  Sort_param m_sort_param;
 
  // TODO(sgunders): Change tables to a table_map; however, currently
  // some semijoin tables are missing from query_block->leaf_tables,
  // so we can't do that yet.
  Filesort(THD *thd, Mem_root_array<TABLE *> tables, bool keep_buffers,
           ORDER *order, ha_rows limit_arg, bool remove_duplicates,
           bool force_sort_rowids, bool unwrap_rollup);
 
  Addon_fields *get_addon_fields(Addon_fields_status *addon_fields_status,
                                 uint *plength, uint *ppackable_length);
 
  // Number of elements in the sortorder array.
  uint sort_order_length() const { return m_sort_order_length; }
 
  /// Whether we are using addon fields (sort entire rows) or not (sort row
  /// IDs). Note that on the first call, this actually makes Sort_param
  /// compute the decision and cache it, so it cannot be called before the sort
  /// order is properly set up.
  bool using_addon_fields();
 
  /// Reset the decision made in using_addon_fields(). Only used in exceptional
  /// circumstances (see NewWeedoutAccessPathForTables()).
  void clear_addon_fields();
 
 private:
  /* Prepare ORDER BY list for sorting. */
  uint make_sortorder(ORDER *order, bool unwrap_rollup);
 
  uint m_sort_order_length;
};
 
bool filesort(THD *thd, Filesort *filesort, RowIterator *source_iterator,
              table_map tables_to_get_rowid_for, ha_rows num_rows_estimate,
              Filesort_info *fs_info, Sort_result *sort_result,
              ha_rows *found_rows);
void filesort_free_buffers(TABLE *table, bool full);
void change_double_for_sort(double nr, uchar *to);
 
/// Declared here so we can unit test it.
uint sortlength(THD *thd, st_sort_field *sortorder, uint s_length);
 
// Avoid pulling in sql/field.h.
template <bool Is_big_endian>
void copy_integer(uchar *to, size_t to_length, const uchar *from,
                  size_t from_length, bool is_unsigned);
 
// Returns whether a sort involving this table would necessarily be on row ID,
// even if not forced by other means.
bool SortWillBeOnRowId(const TABLE *table);
 
static inline void copy_native_longlong(uchar *to, size_t to_length,
                                        longlong val, bool is_unsigned) {
#ifdef WORDS_BIGENDIAN
  constexpr bool Is_big_endian = true;
#else
  constexpr bool Is_big_endian = false;
#endif
  copy_integer<Is_big_endian>(to, to_length,
                              static_cast<uchar *>(static_cast<void *>(&val)),
                              sizeof(longlong), is_unsigned);
}
 
#endif /* FILESORT_INCLUDED */