reverse_index_range_scan.h

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#ifndef SQL_RANGE_OPTIMIZER_REVERSE_INDEX_RANGE_SCAN_H_
#define SQL_RANGE_OPTIMIZER_REVERSE_INDEX_RANGE_SCAN_H_
 
#include <sys/types.h>
 
#include "sql/range_optimizer/index_range_scan.h"
#include "sql/range_optimizer/range_optimizer.h"
#include "sql/sql_list.h"
 
/**
  An iterator much like IndexRangeScanIterator, but it scans in the reverse
  order. This makes it at times more complicated, but since it doesn't support
  being a part of a ROR scan, it is also less complicated in many ways.
 
  One could argue that this and IndexRangeScanIterator should be factored into
  a common base class with separate _ASC and _DESC classes, but they don't
  actually duplicate that much code.
 */
class ReverseIndexRangeScanIterator : public TableRowIterator {
 public:
  ReverseIndexRangeScanIterator(THD *thd, TABLE *table, ha_rows *examined_rows,
                                double expected_rows, uint index,
                                MEM_ROOT *return_mem_root, uint mrr_flags,
                                Bounds_checked_array<QUICK_RANGE *> ranges,
                                bool using_extended_key_parts);
  ~ReverseIndexRangeScanIterator() override;
  int Read() override;
  bool Init() override;
 
 private:
  static range_seq_t quick_range_rev_seq_init(void *init_param, uint, uint);
 
  const uint m_index; /* Index this quick select uses */
  const double m_expected_rows;
  ha_rows *m_examined_rows;
 
  MEM_ROOT *mem_root;
  bool inited = false;
 
  // TODO: pre-allocate space to avoid malloc/free for small number of columns.
  MY_BITMAP column_bitmap;
 
  uint m_mrr_flags; /* Flags to be used with MRR interface */
 
  Bounds_checked_array<QUICK_RANGE *> ranges; /* ordered array of range ptrs */
  /* Members needed to use the MRR interface */
  QUICK_RANGE_SEQ_CTX qr_traversal_ctx;
 
  QUICK_RANGE *last_range;  // The range we are currently scanning, or nullptr.
  int current_range_idx;
 
  /* Info about index we're scanning */
  KEY_PART_INFO *key_part_info;
 
  // Whether this reverse scan uses extended keyparts (in case of Innodb,
  // secondary index is extended to include primary key).
  bool m_using_extended_key_parts{false};
 
  bool range_reads_after_key(QUICK_RANGE *range);
  int cmp_prev(QUICK_RANGE *range);
};
 
#endif  // SQL_RANGE_OPTIMIZER_REVERSE_INDEX_RANGE_SCAN_H_