SEL_TREE Class Reference

#include <tree.h>

Public Types
enum	Type { IMPOSSIBLE , ALWAYS , KEY }
	Starting an effort to document this field: More...

Public Member Functions
	SEL_TREE (enum Type type_arg, MEM_ROOT *root, size_t num_keys)
	SEL_TREE (MEM_ROOT *root, size_t num_keys)
	SEL_TREE (SEL_TREE *arg, RANGE_OPT_PARAM *param)
	Constructor that performs deep-copy of the SEL_ARG trees in 'keys[]' and the index merge alternatives in 'merges'. More...
SEL_ROOT *	release_key (int index)
	Convenience function for removing an element in keys[]. More...
void	set_key (int index, SEL_ROOT *key)
	Convenience function for changing an element in keys[], including updating the use_count. More...

Public Attributes
enum SEL_TREE::Type	type
bool	inexact = false
	Whether this SEL_TREE is an inexact (too broad) representation of the predicates it is based on; that is, if it does not necessarily subsume all of them. More...
Mem_root_array< SEL_ROOT * >	keys
Key_map	keys_map
List< SEL_IMERGE >	merges
Key_map	ror_scans_map
uint	n_ror_scans

Member Enumeration Documentation

Type

enum SEL_TREE::Type

Starting an effort to document this field:

IMPOSSIBLE: if keys[i]->type == SEL_ROOT::Type::IMPOSSIBLE for some i, then type == SEL_TREE::IMPOSSIBLE. Rationale: if the predicate for one of the indexes is always false, then the full predicate is also always false.

ALWAYS: if either (keys[i]->is_always()) or (keys[i] == NULL) for all i, then type == SEL_TREE::ALWAYS. Rationale: the range access method will not be able to filter out any rows when there are no range predicates that can be used to filter on any index.

KEY: There are range predicates that can be used on at least one index.

Enumerator
IMPOSSIBLE
ALWAYS
KEY

Constructor & Destructor Documentation

SEL_TREE() [1/3]

SEL_TREE::SEL_TREE ( enum Type  type_arg, MEM_ROOT *  root, size_t  num_keys  )

inline

SEL_TREE() [2/3]

SEL_TREE::SEL_TREE ( MEM_ROOT *  root, size_t  num_keys  )

inline

SEL_TREE() [3/3]

SEL_TREE::SEL_TREE	(	SEL_TREE *	arg,
		RANGE_OPT_PARAM *	param
	)

Constructor that performs deep-copy of the SEL_ARG trees in 'keys[]' and the index merge alternatives in 'merges'.

Parameters

arg	The SEL_TREE to copy
param	Parameters for range analysis

Member Function Documentation

release_key()

SEL_ROOT * SEL_TREE::release_key ( int  index )

inline

Convenience function for removing an element in keys[].

The typical use for this function is to disconnect the next_key_part from the root, send it to key_and() or key_or(), and then connect the result of that function back to the SEL_ROOT using set_key().

Parameters

index

Which index slot to release.

Returns

The value in the slot (before removal).

set_key()

void SEL_TREE::set_key ( int  index, SEL_ROOT *  key  )

inline

Convenience function for changing an element in keys[], including updating the use_count.

Parameters

index	Which index slot to change.
key	The new contents of the index slot. Is allowed to be nullptr.

Member Data Documentation

inexact

bool SEL_TREE::inexact = false

Whether this SEL_TREE is an inexact (too broad) representation of the predicates it is based on; that is, if it does not necessarily subsume all of them.

Note that a nullptr return from get_mm_tree() (which means “could not generate a tree from this predicate”) is by definition inexact.

There are two main ways a SEL_TREE can become inexact:

• The predicate references fields not contained in any indexes tracked by the SEL_TREE.
• The predicate could be of a form that is not representable as a range. E.g., x > 30 is a range, x mod 2 = 1 is not (although it could in theory be converted to a large amount of disjunct ranges).

If a SEL_TREE is inexact, the predicates must be rechecked after the range scan, using a filter. (Note that it is never too narrow, only ever exact or too broad.) The old join optimizer always does this, no matter what the inexact flag is set to.

Note that additional checks are needed to subsume a predicate even if inexact == false. In particular, SEL_TREE contains information for all indexes over a table, but if a regular range scan is chosen, it can use only one index. So one must then go through all predicates to see if they refer to fields not contained in the given index. Furthermore, range scans on composite (multi-part) indexes can drop predicates on the later keyparts (making predicates on those keyparts inexact), since range scans only support inequalities on the last keypart in any given range. This check must be done in get_ranges_from_tree().

keys

Mem_root_array<SEL_ROOT *> SEL_TREE::keys

keys_map

Key_map SEL_TREE::keys_map

merges

List<SEL_IMERGE> SEL_TREE::merges

n_ror_scans

uint SEL_TREE::n_ror_scans

ror_scans_map

Key_map SEL_TREE::ror_scans_map

type

enum SEL_TREE::Type SEL_TREE::type

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The documentation for this class was generated from the following files:

• sql/range_optimizer/tree.h
• sql/range_optimizer/tree.cc