anonymous_namespace{join_optimizer.cc}::CostingReceiver Class Reference

CostingReceiver contains the main join planning logic, selecting access paths based on cost. More...

Classes
struct	AccessPathSet
	Besides the access paths for a set of nodes (see m_access_paths), AccessPathSet contains information that is common between all access paths for that set. More...

Public Member Functions
	CostingReceiver (THD *thd, Query_block *query_block, JoinHypergraph &graph, const LogicalOrderings *orderings, const Mem_root_array< SortAheadOrdering > *sort_ahead_orderings, const Mem_root_array< ActiveIndexInfo > *active_indexes, const Mem_root_array< FullTextIndexInfo > *fulltext_searches, NodeMap fulltext_tables, uint64_t sargable_fulltext_predicates, table_map update_delete_target_tables, table_map immediate_update_delete_candidates, bool need_rowid, SecondaryEngineFlags engine_flags, int subgraph_pair_limit, secondary_engine_modify_access_path_cost_t secondary_engine_cost_hook, string *trace)
CostingReceiver &	operator= (const CostingReceiver &)=delete
CostingReceiver &	operator= (CostingReceiver &&)=default
	CostingReceiver (const CostingReceiver &)=delete
	CostingReceiver (CostingReceiver &&)=default
bool	HasSeen (NodeMap subgraph) const
bool	FoundSingleNode (int node_idx)
bool	FoundSubgraphPair (NodeMap left, NodeMap right, int edge_idx)
const Prealloced_array< AccessPath *, 4 > &	root_candidates ()
FunctionalDependencySet	active_fds_at_root () const
size_t	num_subplans () const
size_t	num_access_paths () const
bool	always_empty () const
	True if the result of the join is found to be always empty, typically because of an impossible WHERE clause. More...
AccessPath *	ProposeAccessPath (AccessPath *path, Prealloced_array< AccessPath *, 4 > *existing_paths, OrderingSet obsolete_orderings, const char *description_for_trace) const
bool	HasSecondaryEngineCostHook () const

Private Member Functions
string	PrintSet (NodeMap x) const
	For trace use only. More...
string	PrintSubgraphHeader (const JoinPredicate *edge, const AccessPath &join_path, NodeMap left, NodeMap right) const
	For trace use only. More...
bool	SupportedEngineFlag (SecondaryEngineFlag flag) const
	Checks whether the given engine flag is active or not. More...
bool	FindIndexRangeScans (int node_idx, bool *impossible, double *num_output_rows_after_filter)
void	ProposeIndexMerge (TABLE *table, int node_idx, const SEL_IMERGE &imerge, int pred_idx, bool inexact, bool allow_clustered_primary_key_scan, int num_where_predicates, double num_output_rows_after_filter, RANGE_OPT_PARAM *param, bool *has_clustered_primary_key_scan)
void	TraceAccessPaths (NodeMap nodes)
void	ProposeAccessPathForBaseTable (int node_idx, double force_num_output_rows_after_filter, const char *description_for_trace, AccessPath *path)
void	ProposeAccessPathForIndex (int node_idx, OverflowBitset applied_predicates, OverflowBitset subsumed_predicates, double force_num_output_rows_after_filter, const char *description_for_trace, AccessPath *path)
void	ProposeAccessPathWithOrderings (NodeMap nodes, FunctionalDependencySet fd_set, OrderingSet obsolete_orderings, AccessPath *path, const char *description_for_trace)
bool	ProposeTableScan (TABLE *table, int node_idx, double force_num_output_rows_after_filter)
bool	ProposeIndexScan (TABLE *table, int node_idx, double force_num_output_rows_after_filter, unsigned key_idx, bool reverse, int ordering_idx)
bool	ProposeRefAccess (TABLE *table, int node_idx, unsigned key_idx, double force_num_output_rows_after_filter, bool reverse, table_map allowed_parameter_tables, int ordering_idx)
bool	ProposeAllUniqueIndexLookupsWithConstantKey (int node_idx, bool *found)
bool	RedundantThroughSargable (OverflowBitset redundant_against_sargable_predicates, const AccessPath *left_path, const AccessPath *right_path, NodeMap left, NodeMap right)
pair< bool, bool >	AlreadyAppliedAsSargable (Item *condition, const AccessPath *left_path, const AccessPath *right_path)
bool	ProposeAllFullTextIndexScans (TABLE *table, int node_idx, double force_num_output_rows_after_filter)
bool	ProposeFullTextIndexScan (TABLE *table, int node_idx, Item_func_match *match, int predicate_idx, int ordering_idx, double force_num_output_rows_after_filter)
void	ProposeNestedLoopJoin (NodeMap left, NodeMap right, AccessPath *left_path, AccessPath *right_path, const JoinPredicate *edge, bool rewrite_semi_to_inner, FunctionalDependencySet new_fd_set, OrderingSet new_obsolete_orderings, bool *wrote_trace)
void	ProposeHashJoin (NodeMap left, NodeMap right, AccessPath *left_path, AccessPath *right_path, const JoinPredicate *edge, FunctionalDependencySet new_fd_set, OrderingSet new_obsolete_orderings, bool rewrite_semi_to_inner, bool *wrote_trace)
void	ApplyPredicatesForBaseTable (int node_idx, OverflowBitset applied_predicates, OverflowBitset subsumed_predicates, bool materialize_subqueries, AccessPath *path, FunctionalDependencySet *new_fd_set)
void	ApplyDelayedPredicatesAfterJoin (NodeMap left, NodeMap right, const AccessPath *left_path, const AccessPath *right_path, int join_predicate_first, int join_predicate_last, bool materialize_subqueries, AccessPath *join_path, FunctionalDependencySet *new_fd_set)
double	FindAlreadyAppliedSelectivity (const JoinPredicate *edge, const AccessPath *left_path, const AccessPath *right_path, NodeMap left, NodeMap right)
void	CommitBitsetsToHeap (AccessPath *path) const
bool	BitsetsAreCommitted (AccessPath *path) const

Private Attributes
THD *	m_thd
Query_block *	m_query_block
	The query block we are planning. More...
mem_root_unordered_map< NodeMap, AccessPathSet >	m_access_paths
	For each subset of tables that are connected in the join hypergraph, keeps the current best access paths for producing said subset. More...
int	m_num_seen_subgraph_pairs = 0
	How many subgraph pairs we've seen so far. More...
JoinHypergraph *	m_graph
	The graph we are running over. More...
bool	has_clamped_multipart_eq_ref = false
	Whether we have applied clamping due to a multi-column EQ_REF at any point. More...
bool	has_semijoin_with_possibly_clamped_child = false
	Whether we have a semijoin where the inner child is parameterized on the outer child, and the row estimate of the inner child is possibly clamped, for example because of some other semijoin. More...
const LogicalOrderings *	m_orderings
	Keeps track of interesting orderings in this query block. More...
const Mem_root_array< SortAheadOrdering > *	m_sort_ahead_orderings
	List of all orderings that are candidates for sort-ahead (because they are, or may eventually become, an interesting ordering). More...
const Mem_root_array< ActiveIndexInfo > *	m_active_indexes
	List of all indexes that are active and that we can apply in this query. More...
const Mem_root_array< FullTextIndexInfo > *	m_fulltext_searches
	List of all active full-text indexes that we can apply in this query. More...
NodeMap	m_fulltext_tables = 0
	A map of tables that are referenced by a MATCH function (those tables that have Table_ref::is_fulltext_searched() == true). More...
uint64_t	m_sargable_fulltext_predicates = 0
	The set of WHERE predicates which are on a form that can be satisfied by a full-text index scan. More...
NodeMap	m_update_delete_target_nodes = 0
	The target tables of an UPDATE or DELETE statement. More...
NodeMap	m_immediate_update_delete_candidates = 0
	The set of tables that are candidates for immediate update or delete. More...
bool	m_need_rowid
	Whether we will be needing row IDs from our tables, typically for a later sort. More...
SecondaryEngineFlags	m_engine_flags
	The flags declared by the secondary engine. More...
int	m_subgraph_pair_limit
	The maximum number of pairs of subgraphs we are willing to accept, or -1 if no limit. More...
secondary_engine_modify_access_path_cost_t	m_secondary_engine_cost_hook
	Pointer to a function that modifies the cost estimates of an access path for execution in a secondary storage engine, or nullptr otherwise. More...
string *	m_trace
	If not nullptr, we store human-readable optimizer trace information here. More...
NodeMap	forced_leftmost_table = 0
	A map of tables that can never be on the right side of any join, ie., they have to be leftmost in the tree. More...
MEM_ROOT	m_overflow_bitset_mem_root
	A special MEM_ROOT for allocating OverflowBitsets that we might end up discarding, ie. More...
MEM_ROOT	m_range_optimizer_mem_root
	A special MEM_ROOT for temporary data for the range optimizer. More...

Detailed Description

CostingReceiver contains the main join planning logic, selecting access paths based on cost.

It receives subplans from DPhyp (see enumerate_subgraph.h), assigns them costs based on a cost model, and keeps the ones that are cheapest. In the end, this means it will be left with a root access path that gives the lowest total cost for joining the tables in the query block, ie., without ORDER BY etc.

Currently, besides the expected number of produced rows (which is the same no matter how we access the table) we keep only a single value per subplan (total cost), and thus also only a single best access path. In the future, we will have more dimensions to worry about, such as initial cost versus total cost (relevant for LIMIT), ordering properties, and so on. At that point, there is not necessarily a single “best” access path anymore, and we will need to keep multiple ones around, and test all of them as candidates when building larger subplans.

Constructor & Destructor Documentation

CostingReceiver() [1/3]

anonymous_namespace{join_optimizer.cc}::CostingReceiver::CostingReceiver ( THD *  thd, Query_block *  query_block, JoinHypergraph &  graph, const LogicalOrderings *  orderings, const Mem_root_array< SortAheadOrdering > *  sort_ahead_orderings, const Mem_root_array< ActiveIndexInfo > *  active_indexes, const Mem_root_array< FullTextIndexInfo > *  fulltext_searches, NodeMap  fulltext_tables, uint64_t  sargable_fulltext_predicates, table_map  update_delete_target_tables, table_map  immediate_update_delete_candidates, bool  need_rowid, SecondaryEngineFlags  engine_flags, int  subgraph_pair_limit, secondary_engine_modify_access_path_cost_t  secondary_engine_cost_hook, string *  trace  )

inline

CostingReceiver() [2/3]

anonymous_namespace{join_optimizer.cc}::CostingReceiver::CostingReceiver ( const CostingReceiver &  )

delete

CostingReceiver() [3/3]

anonymous_namespace{join_optimizer.cc}::CostingReceiver::CostingReceiver ( CostingReceiver &&  )

default

Member Function Documentation

active_fds_at_root()

FunctionalDependencySet anonymous_namespace{join_optimizer.cc}::CostingReceiver::active_fds_at_root ( ) const

inline

AlreadyAppliedAsSargable()

pair< bool, bool > anonymous_namespace{join_optimizer.cc}::CostingReceiver::AlreadyAppliedAsSargable ( Item *  condition, const AccessPath *  left_path, const AccessPath *  right_path  )

inlineprivate

always_empty()

bool anonymous_namespace{join_optimizer.cc}::CostingReceiver::always_empty ( ) const

inline

True if the result of the join is found to be always empty, typically because of an impossible WHERE clause.

ApplyDelayedPredicatesAfterJoin()

void anonymous_namespace{join_optimizer.cc}::CostingReceiver::ApplyDelayedPredicatesAfterJoin ( NodeMap  left, NodeMap  right, const AccessPath *  left_path, const AccessPath *  right_path, int  join_predicate_first, int  join_predicate_last, bool  materialize_subqueries, AccessPath *  join_path, FunctionalDependencySet *  new_fd_set  )

private

ApplyPredicatesForBaseTable()

void anonymous_namespace{join_optimizer.cc}::CostingReceiver::ApplyPredicatesForBaseTable ( int  node_idx, OverflowBitset  applied_predicates, OverflowBitset  subsumed_predicates, bool  materialize_subqueries, AccessPath *  path, FunctionalDependencySet *  new_fd_set  )

private

BitsetsAreCommitted()

bool anonymous_namespace{join_optimizer.cc}::CostingReceiver::BitsetsAreCommitted ( AccessPath *  path ) const

private

CommitBitsetsToHeap()

void anonymous_namespace{join_optimizer.cc}::CostingReceiver::CommitBitsetsToHeap ( AccessPath *  path ) const

private

FindAlreadyAppliedSelectivity()

double anonymous_namespace{join_optimizer.cc}::CostingReceiver::FindAlreadyAppliedSelectivity ( const JoinPredicate *  edge, const AccessPath *  left_path, const AccessPath *  right_path, NodeMap  left, NodeMap  right  )

private

FindIndexRangeScans()

bool anonymous_namespace{join_optimizer.cc}::CostingReceiver::FindIndexRangeScans ( int  node_idx, bool *  impossible, double *  num_output_rows_after_filter  )

private

FoundSingleNode()

bool anonymous_namespace{join_optimizer.cc}::CostingReceiver::FoundSingleNode

(

int

node_idx

)

FoundSubgraphPair()

bool anonymous_namespace{join_optimizer.cc}::CostingReceiver::FoundSubgraphPair	(	NodeMap	left,
		NodeMap	right,
		int	edge_idx
	)

HasSecondaryEngineCostHook()

bool anonymous_namespace{join_optimizer.cc}::CostingReceiver::HasSecondaryEngineCostHook ( ) const

inline

HasSeen()

bool anonymous_namespace{join_optimizer.cc}::CostingReceiver::HasSeen ( NodeMap  subgraph ) const

inline

num_access_paths()

size_t anonymous_namespace{join_optimizer.cc}::CostingReceiver::num_access_paths ( ) const

inline

num_subplans()

size_t anonymous_namespace{join_optimizer.cc}::CostingReceiver::num_subplans ( ) const

inline

operator=() [1/2]

CostingReceiver & anonymous_namespace{join_optimizer.cc}::CostingReceiver::operator= ( const CostingReceiver &  )

delete

operator=() [2/2]

CostingReceiver & anonymous_namespace{join_optimizer.cc}::CostingReceiver::operator= ( CostingReceiver &&  )

default

PrintSet()

string anonymous_namespace{join_optimizer.cc}::CostingReceiver::PrintSet ( NodeMap  x ) const

inlineprivate

For trace use only.

PrintSubgraphHeader()

string anonymous_namespace{join_optimizer.cc}::CostingReceiver::PrintSubgraphHeader ( const JoinPredicate *  edge, const AccessPath &  join_path, NodeMap  left, NodeMap  right  ) const

private

For trace use only.

ProposeAccessPath()

AccessPath * anonymous_namespace{join_optimizer.cc}::CostingReceiver::ProposeAccessPath	(	AccessPath *	path,
		Prealloced_array< AccessPath *, 4 > *	existing_paths,
		OrderingSet	obsolete_orderings,
		const char *	description_for_trace
	)		const

ProposeAccessPathForBaseTable()

void anonymous_namespace{join_optimizer.cc}::CostingReceiver::ProposeAccessPathForBaseTable ( int  node_idx, double  force_num_output_rows_after_filter, const char *  description_for_trace, AccessPath *  path  )

private

ProposeAccessPathForIndex()

void anonymous_namespace{join_optimizer.cc}::CostingReceiver::ProposeAccessPathForIndex ( int  node_idx, OverflowBitset  applied_predicates, OverflowBitset  subsumed_predicates, double  force_num_output_rows_after_filter, const char *  description_for_trace, AccessPath *  path  )

private

ProposeAccessPathWithOrderings()

void anonymous_namespace{join_optimizer.cc}::CostingReceiver::ProposeAccessPathWithOrderings ( NodeMap  nodes, FunctionalDependencySet  fd_set, OrderingSet  obsolete_orderings, AccessPath *  path, const char *  description_for_trace  )

private

ProposeAllFullTextIndexScans()

bool anonymous_namespace{join_optimizer.cc}::CostingReceiver::ProposeAllFullTextIndexScans ( TABLE *  table, int  node_idx, double  force_num_output_rows_after_filter  )

private

ProposeAllUniqueIndexLookupsWithConstantKey()

bool anonymous_namespace{join_optimizer.cc}::CostingReceiver::ProposeAllUniqueIndexLookupsWithConstantKey ( int  node_idx, bool *  found  )

private

ProposeFullTextIndexScan()

bool anonymous_namespace{join_optimizer.cc}::CostingReceiver::ProposeFullTextIndexScan ( TABLE *  table, int  node_idx, Item_func_match *  match, int  predicate_idx, int  ordering_idx, double  force_num_output_rows_after_filter  )

private

ProposeHashJoin()

void anonymous_namespace{join_optimizer.cc}::CostingReceiver::ProposeHashJoin ( NodeMap  left, NodeMap  right, AccessPath *  left_path, AccessPath *  right_path, const JoinPredicate *  edge, FunctionalDependencySet  new_fd_set, OrderingSet  new_obsolete_orderings, bool  rewrite_semi_to_inner, bool *  wrote_trace  )

private

ProposeIndexMerge()

void anonymous_namespace{join_optimizer.cc}::CostingReceiver::ProposeIndexMerge ( TABLE *  table, int  node_idx, const SEL_IMERGE &  imerge, int  pred_idx, bool  inexact, bool  allow_clustered_primary_key_scan, int  num_where_predicates, double  num_output_rows_after_filter, RANGE_OPT_PARAM *  param, bool *  has_clustered_primary_key_scan  )

private

ProposeIndexScan()

bool anonymous_namespace{join_optimizer.cc}::CostingReceiver::ProposeIndexScan ( TABLE *  table, int  node_idx, double  force_num_output_rows_after_filter, unsigned  key_idx, bool  reverse, int  ordering_idx  )

private

ProposeNestedLoopJoin()

void anonymous_namespace{join_optimizer.cc}::CostingReceiver::ProposeNestedLoopJoin ( NodeMap  left, NodeMap  right, AccessPath *  left_path, AccessPath *  right_path, const JoinPredicate *  edge, bool  rewrite_semi_to_inner, FunctionalDependencySet  new_fd_set, OrderingSet  new_obsolete_orderings, bool *  wrote_trace  )

private

ProposeRefAccess()

bool anonymous_namespace{join_optimizer.cc}::CostingReceiver::ProposeRefAccess ( TABLE *  table, int  node_idx, unsigned  key_idx, double  force_num_output_rows_after_filter, bool  reverse, table_map  allowed_parameter_tables, int  ordering_idx  )

private

ProposeTableScan()

bool anonymous_namespace{join_optimizer.cc}::CostingReceiver::ProposeTableScan ( TABLE *  table, int  node_idx, double  force_num_output_rows_after_filter  )

private

RedundantThroughSargable()

bool anonymous_namespace{join_optimizer.cc}::CostingReceiver::RedundantThroughSargable ( OverflowBitset  redundant_against_sargable_predicates, const AccessPath *  left_path, const AccessPath *  right_path, NodeMap  left, NodeMap  right  )

private

root_candidates()

const Prealloced_array< AccessPath *, 4 > & anonymous_namespace{join_optimizer.cc}::CostingReceiver::root_candidates ( )

inline

SupportedEngineFlag()

bool anonymous_namespace{join_optimizer.cc}::CostingReceiver::SupportedEngineFlag ( SecondaryEngineFlag  flag ) const

inlineprivate

Checks whether the given engine flag is active or not.

TraceAccessPaths()

void anonymous_namespace{join_optimizer.cc}::CostingReceiver::TraceAccessPaths ( NodeMap  nodes )

private

Member Data Documentation

forced_leftmost_table

NodeMap anonymous_namespace{join_optimizer.cc}::CostingReceiver::forced_leftmost_table = 0

private

A map of tables that can never be on the right side of any join, ie., they have to be leftmost in the tree.

This only affects recursive table references (ie., when WITH RECURSIVE is in use); they work by continuously tailing new records, which wouldn't work if we were to scan them multiple times or put them in a hash table. Naturally, there must be zero or one bit here; the common case is zero.

has_clamped_multipart_eq_ref

bool anonymous_namespace{join_optimizer.cc}::CostingReceiver::has_clamped_multipart_eq_ref = false

private

Whether we have applied clamping due to a multi-column EQ_REF at any point.

There is a known issue (see bug #33550360) where this can cause row count estimates to be inconsistent between different access paths. Obviously, we should fix this bug by adjusting the selectivities (and we do for single-column indexes), but for multipart indexes, this is nontrivial. See the bug for details on some ideas, but the gist of it is that we probably will want a linear program to adjust multi-selectivities so that they are consistent, and not above 1/N (for N-row tables) if there are unique indexes on them.

The only reason why we collect this information, like JoinHypergraph::has_reordered_left_joins, is to be able to assert on inconsistent row counts between APs, excluding this (known) issue.

has_semijoin_with_possibly_clamped_child

bool anonymous_namespace{join_optimizer.cc}::CostingReceiver::has_semijoin_with_possibly_clamped_child = false

private

Whether we have a semijoin where the inner child is parameterized on the outer child, and the row estimate of the inner child is possibly clamped, for example because of some other semijoin.

In this case, we may see inconsistent row count estimates between the ordinary semijoin plan and the rewrite_semi_to_inner plan, because it's hard to tell how much the already-applied-as-sargable selectivity affected the row count estimate of the child.

The only reason why we collect this information, is to be able to assert on inconsistent row counts between access paths, excluding this known issue.

m_access_paths

mem_root_unordered_map<NodeMap, AccessPathSet> anonymous_namespace{join_optimizer.cc}::CostingReceiver::m_access_paths

private

For each subset of tables that are connected in the join hypergraph, keeps the current best access paths for producing said subset.

There can be several that are best in different ways; see comments on ProposeAccessPath().

Also used for communicating connectivity information back to DPhyp (in HasSeen()); if there's an entry here, that subset will induce a connected subgraph of the join hypergraph.

m_active_indexes

const Mem_root_array<ActiveIndexInfo>* anonymous_namespace{join_optimizer.cc}::CostingReceiver::m_active_indexes

private

List of all indexes that are active and that we can apply in this query.

Indexes can be useful in several ways: We can use them for ref access, for index-only scans, or to get interesting orderings.

m_engine_flags

SecondaryEngineFlags anonymous_namespace{join_optimizer.cc}::CostingReceiver::m_engine_flags

private

The flags declared by the secondary engine.

In particular, it describes what kind of access path types should not be created.

m_fulltext_searches

const Mem_root_array<FullTextIndexInfo>* anonymous_namespace{join_optimizer.cc}::CostingReceiver::m_fulltext_searches

private

List of all active full-text indexes that we can apply in this query.

m_fulltext_tables

NodeMap anonymous_namespace{join_optimizer.cc}::CostingReceiver::m_fulltext_tables = 0

private

A map of tables that are referenced by a MATCH function (those tables that have Table_ref::is_fulltext_searched() == true).

It is used for preventing hash joins involving tables that are full-text searched.

m_graph

JoinHypergraph* anonymous_namespace{join_optimizer.cc}::CostingReceiver::m_graph

private

The graph we are running over.

m_immediate_update_delete_candidates

NodeMap anonymous_namespace{join_optimizer.cc}::CostingReceiver::m_immediate_update_delete_candidates = 0

private

The set of tables that are candidates for immediate update or delete.

Immediate update/delete means that the rows from the table are deleted while reading the rows from the topmost iterator. (As opposed to buffered update/delete, where the row IDs are stored in temporary tables, and only updated or deleted after the topmost iterator has been read to the end.) The candidates are those target tables that are only referenced once in the query. The requirement for immediate deletion is that the deleted row will not have to be read again later. Currently, at most one of the candidate tables is chosen, and it is always the outermost table in the join tree.

m_need_rowid

bool anonymous_namespace{join_optimizer.cc}::CostingReceiver::m_need_rowid

private

Whether we will be needing row IDs from our tables, typically for a later sort.

If this happens, derived tables cannot use streaming, but need an actual materialization, since filesort expects to be able to go back and ask for a given row. (This is different from when we need row IDs for weedout, which doesn't preclude streaming. The hypergraph optimizer does not use weedout.)

m_num_seen_subgraph_pairs

int anonymous_namespace{join_optimizer.cc}::CostingReceiver::m_num_seen_subgraph_pairs = 0

private

How many subgraph pairs we've seen so far.

Used to give up if we end up allocating too many resources (prompting us to create a simpler join graph and try again).

m_orderings

const LogicalOrderings* anonymous_namespace{join_optimizer.cc}::CostingReceiver::m_orderings

private

Keeps track of interesting orderings in this query block.

See LogicalOrderings for more information.

m_overflow_bitset_mem_root

MEM_ROOT anonymous_namespace{join_optimizer.cc}::CostingReceiver::m_overflow_bitset_mem_root

private

A special MEM_ROOT for allocating OverflowBitsets that we might end up discarding, ie.

for AccessPaths that do not yet live in m_access_paths. For any AccessPath that is to have a permanent life (ie., not be immediately discarded as inferior), the OverflowBitset must be taken out of this MEM_ROOT and onto the regular one, as it is cleared often. (This significantly reduces the amount of memory used in situations where lots of AccessPaths are produced and discarded. Of course, it only matters for queries with >= 64 predicates.)

The copying is using CommitBitsetsToHeap(). ProposeAccessPath() will automatically call CommitBitsetsToHeap() for accepted access paths, but it will not call it on any of their children. Thus, if you've added more than one AccessPath in the chain (e.g. if you add a join, then a sort of that join, and then propose the sort), you will need to make sure there are no stray bitsets left on this MEM_ROOT.

Because this can be a source of subtle bugs, you should be conservative about what bitsets you put here; really, only the ones you could be allocating many of (like joins) should be candidates.

m_query_block

Query_block* anonymous_namespace{join_optimizer.cc}::CostingReceiver::m_query_block

private

The query block we are planning.

m_range_optimizer_mem_root

MEM_ROOT anonymous_namespace{join_optimizer.cc}::CostingReceiver::m_range_optimizer_mem_root

private

A special MEM_ROOT for temporary data for the range optimizer.

It can be discarded immediately after we've decided on the range scans for a given table (but we reuse its memory as long as there are more tables left to scan).

m_sargable_fulltext_predicates

uint64_t anonymous_namespace{join_optimizer.cc}::CostingReceiver::m_sargable_fulltext_predicates = 0

private

The set of WHERE predicates which are on a form that can be satisfied by a full-text index scan.

This includes calls to MATCH with no comparison operator, and predicates on the form MATCH > const or MATCH >= const (where const must be high enough to make the comparison return false for documents with zero score).

m_secondary_engine_cost_hook

secondary_engine_modify_access_path_cost_t anonymous_namespace{join_optimizer.cc}::CostingReceiver::m_secondary_engine_cost_hook

private

Pointer to a function that modifies the cost estimates of an access path for execution in a secondary storage engine, or nullptr otherwise.

m_sort_ahead_orderings

const Mem_root_array<SortAheadOrdering>* anonymous_namespace{join_optimizer.cc}::CostingReceiver::m_sort_ahead_orderings

private

List of all orderings that are candidates for sort-ahead (because they are, or may eventually become, an interesting ordering).

m_subgraph_pair_limit

int anonymous_namespace{join_optimizer.cc}::CostingReceiver::m_subgraph_pair_limit

private

The maximum number of pairs of subgraphs we are willing to accept, or -1 if no limit.

If this limit gets hit, we stop traversing the graph and return an error; the caller will then have to modify the hypergraph (see GraphSimplifier) to make for a graph with fewer options, so that planning time will come under an acceptable limit.

m_thd

THD* anonymous_namespace{join_optimizer.cc}::CostingReceiver::m_thd

private

m_trace

string* anonymous_namespace{join_optimizer.cc}::CostingReceiver::m_trace

private

If not nullptr, we store human-readable optimizer trace information here.

m_update_delete_target_nodes

NodeMap anonymous_namespace{join_optimizer.cc}::CostingReceiver::m_update_delete_target_nodes = 0

private

The target tables of an UPDATE or DELETE statement.

---

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

• sql/join_optimizer/join_optimizer.cc