interesting_orders_defs.h

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#ifndef SQL_JOIN_OPTIMIZER_INTERESTING_ORDERS_DEFS_H
#define SQL_JOIN_OPTIMIZER_INTERESTING_ORDERS_DEFS_H
 
// Definitions related to interesting_orders.h that can be pulled in
// without additional dependencies on MySQL headers.
 
#include <bitset>
 
enum enum_order : int;
class Item;
class THD;
 
// All Item * are normalized to opaque handles, where handle(x) == handle(y)
// iff x->eq(y, /*binary_cmp=*/true). This makes them faster to compare,
// and as an added bonus, they also take up slightly less memory.
using ItemHandle = int;
 
// Like ORDER, but smaller and easier to handle for our purposes (in particular,
// no double-pointer for item). Designed for planning, not execution, so you
// will need to make a Filesort element out of it eventually.
struct OrderElement {
  ItemHandle item;
 
  // ORDER_NOT_RELEVANT for a group specification. Groupings are by convention
  // sorted by item.
  enum_order direction;
};
 
inline bool operator==(const OrderElement &a, const OrderElement &b) {
  return a.item == b.item && a.direction == b.direction;
}
 
// We represent sets of functional dependencies by bitsets, and for simplicity,
// we only allow a fixed number of them; if you have more of them, they will not
// get their own bitmask and will be silently ignored (imposisble to follow in
// the state machine). Note that this does not include “always-on” FDs and FDs
// that will be pruned away, as these are either removed or silently removed to
// the highest indexes.
static constexpr int kMaxSupportedFDs = 64;
using FunctionalDependencySet = std::bitset<kMaxSupportedFDs>;
 
static constexpr int kMaxSupportedOrderings = 64;
using OrderingSet = std::bitset<kMaxSupportedOrderings>;
 
#endif  // SQL_JOIN_OPTIMIZER_INTERESTING_ORDERS_H