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blue-lemon0104
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db_include/nodes/supportnodes.h
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242
db_include/nodes/supportnodes.h
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/*-------------------------------------------------------------------------
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*
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* supportnodes.h
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* Definitions for planner support functions.
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*
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* This file defines the API for "planner support functions", which
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* are SQL functions (normally written in C) that can be attached to
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* another "target" function to give the system additional knowledge
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* about the target function. All the current capabilities have to do
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* with planning queries that use the target function, though it is
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* possible that future extensions will add functionality to be invoked
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* by the parser or executor.
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*
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* A support function must have the SQL signature
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* supportfn(internal) returns internal
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* The argument is a pointer to one of the Node types defined in this file.
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* The result is usually also a Node pointer, though its type depends on
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* which capability is being invoked. In all cases, a NULL pointer result
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* (that's PG_RETURN_POINTER(NULL), not PG_RETURN_NULL()) indicates that
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* the support function cannot do anything useful for the given request.
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* Support functions must return a NULL pointer, not fail, if they do not
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* recognize the request node type or cannot handle the given case; this
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* allows for future extensions of the set of request cases.
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*
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*
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* Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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* src/include/nodes/supportnodes.h
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*
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*-------------------------------------------------------------------------
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*/
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#ifndef SUPPORTNODES_H
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#define SUPPORTNODES_H
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#include "nodes/primnodes.h"
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struct PlannerInfo; /* avoid including pathnodes.h here */
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struct IndexOptInfo;
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struct SpecialJoinInfo;
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/*
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* The Simplify request allows the support function to perform plan-time
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* simplification of a call to its target function. For example, a varchar
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* length coercion that does not decrease the allowed length of its argument
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* could be replaced by a RelabelType node, or "x + 0" could be replaced by
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* "x". This is invoked during the planner's constant-folding pass, so the
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* function's arguments can be presumed already simplified.
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*
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* The planner's PlannerInfo "root" is typically not needed, but can be
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* consulted if it's necessary to obtain info about Vars present in
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* the given node tree. Beware that root could be NULL in some usages.
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*
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* "fcall" will be a FuncExpr invoking the support function's target
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* function. (This is true even if the original parsetree node was an
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* operator call; a FuncExpr is synthesized for this purpose.)
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*
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* The result should be a semantically-equivalent transformed node tree,
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* or NULL if no simplification could be performed. Do *not* return or
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* modify *fcall, as it isn't really a separately allocated Node. But
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* it's okay to use fcall->args, or parts of it, in the result tree.
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*/
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typedef struct SupportRequestSimplify
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{
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NodeTag type;
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struct PlannerInfo *root; /* Planner's infrastructure */
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FuncExpr *fcall; /* Function call to be simplified */
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} SupportRequestSimplify;
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/*
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* The Selectivity request allows the support function to provide a
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* selectivity estimate for a function appearing at top level of a WHERE
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* clause (so it applies only to functions returning boolean).
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*
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* The input arguments are the same as are supplied to operator restriction
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* and join estimators, except that we unify those two APIs into just one
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* request type. See clause_selectivity() for the details.
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*
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* If an estimate can be made, store it into the "selectivity" field and
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* return the address of the SupportRequestSelectivity node; the estimate
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* must be between 0 and 1 inclusive. Return NULL if no estimate can be
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* made (in which case the planner will fall back to a default estimate,
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* traditionally 1/3).
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*
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* If the target function is being used as the implementation of an operator,
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* the support function will not be used for this purpose; the operator's
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* restriction or join estimator is consulted instead.
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*/
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typedef struct SupportRequestSelectivity
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{
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NodeTag type;
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/* Input fields: */
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struct PlannerInfo *root; /* Planner's infrastructure */
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Oid funcid; /* function we are inquiring about */
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List *args; /* pre-simplified arguments to function */
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Oid inputcollid; /* function's input collation */
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bool is_join; /* is this a join or restriction case? */
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int varRelid; /* if restriction, RTI of target relation */
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JoinType jointype; /* if join, outer join type */
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struct SpecialJoinInfo *sjinfo; /* if outer join, info about join */
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/* Output fields: */
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Selectivity selectivity; /* returned selectivity estimate */
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} SupportRequestSelectivity;
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/*
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* The Cost request allows the support function to provide an execution
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* cost estimate for its target function. The cost estimate can include
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* both a one-time (query startup) component and a per-execution component.
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* The estimate should *not* include the costs of evaluating the target
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* function's arguments, only the target function itself.
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*
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* The "node" argument is normally the parse node that is invoking the
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* target function. This is a FuncExpr in the simplest case, but it could
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* also be an OpExpr, DistinctExpr, NullIfExpr, or WindowFunc, or possibly
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* other cases in future. NULL is passed if the function cannot presume
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* its arguments to be equivalent to what the calling node presents as
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* arguments; that happens for, e.g., aggregate support functions and
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* per-column comparison operators used by RowExprs.
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*
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* If an estimate can be made, store it into the cost fields and return the
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* address of the SupportRequestCost node. Return NULL if no estimate can be
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* made, in which case the planner will rely on the target function's procost
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* field. (Note: while procost is automatically scaled by cpu_operator_cost,
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* this is not the case for the outputs of the Cost request; the support
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* function must scale its results appropriately on its own.)
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*/
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typedef struct SupportRequestCost
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{
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NodeTag type;
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/* Input fields: */
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struct PlannerInfo *root; /* Planner's infrastructure (could be NULL) */
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Oid funcid; /* function we are inquiring about */
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Node *node; /* parse node invoking function, or NULL */
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/* Output fields: */
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Cost startup; /* one-time cost */
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Cost per_tuple; /* per-evaluation cost */
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} SupportRequestCost;
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/*
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* The Rows request allows the support function to provide an output rowcount
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* estimate for its target function (so it applies only to set-returning
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* functions).
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*
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* The "node" argument is the parse node that is invoking the target function;
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* currently this will always be a FuncExpr or OpExpr.
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*
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* If an estimate can be made, store it into the rows field and return the
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* address of the SupportRequestRows node. Return NULL if no estimate can be
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* made, in which case the planner will rely on the target function's prorows
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* field.
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*/
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typedef struct SupportRequestRows
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{
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NodeTag type;
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/* Input fields: */
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struct PlannerInfo *root; /* Planner's infrastructure (could be NULL) */
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Oid funcid; /* function we are inquiring about */
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Node *node; /* parse node invoking function */
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/* Output fields: */
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double rows; /* number of rows expected to be returned */
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} SupportRequestRows;
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/*
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* The IndexCondition request allows the support function to generate
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* a directly-indexable condition based on a target function call that is
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* not itself indexable. The target function call must appear at the top
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* level of WHERE or JOIN/ON, so this applies only to functions returning
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* boolean.
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*
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* The "node" argument is the parse node that is invoking the target function;
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* currently this will always be a FuncExpr or OpExpr. The call is made
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* only if at least one function argument matches an index column's variable
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* or expression. "indexarg" identifies the matching argument (it's the
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* argument's zero-based index in the node's args list).
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*
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* If the transformation is possible, return a List of directly-indexable
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* condition expressions, else return NULL. (A List is used because it's
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* sometimes useful to generate more than one indexable condition, such as
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* when a LIKE with constant prefix gives rise to both >= and < conditions.)
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*
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* "Directly indexable" means that the condition must be directly executable
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* by the index machinery. Typically this means that it is a binary OpExpr
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* with the index column value on the left, a pseudo-constant on the right,
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* and an operator that is in the index column's operator family. Other
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* possibilities include RowCompareExpr, ScalarArrayOpExpr, and NullTest,
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* depending on the index type; but those seem less likely to be useful for
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* derived index conditions. "Pseudo-constant" means that the right-hand
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* expression must not contain any volatile functions, nor any Vars of the
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* table the index is for; use is_pseudo_constant_for_index() to check this.
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* (Note: if the passed "node" is an OpExpr, the core planner already verified
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* that the non-indexkey operand is pseudo-constant; but when the "node"
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* is a FuncExpr, it does not check, since it doesn't know which of the
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* function's arguments you might need to use in an index comparison value.)
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*
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* In many cases, an index condition can be generated but it is weaker than
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* the function condition itself; for example, a LIKE with a constant prefix
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* can produce an index range check based on the prefix, but we still need
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* to execute the LIKE operator to verify the rest of the pattern. We say
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* that such an index condition is "lossy". When returning an index condition,
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* you should set the "lossy" request field to true if the condition is lossy,
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* or false if it is an exact equivalent of the function's result. The core
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* code will initialize that field to true, which is the common case.
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*
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* It is important to verify that the index operator family is the correct
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* one for the condition you want to generate. Core support functions tend
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* to use the known OID of a built-in opfamily for this, but extensions need
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* to work harder, since their OIDs aren't fixed. A possibly workable
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* answer for an index on an extension datatype is to verify the index AM's
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* OID instead, and then assume that there's only one relevant opclass for
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* your datatype so the opfamily must be the right one. Generating OpExpr
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* nodes may also require knowing extension datatype OIDs (often you can
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* find these out by applying exprType() to a function argument) and
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* operator OIDs (which you can look up using get_opfamily_member).
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*/
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typedef struct SupportRequestIndexCondition
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{
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NodeTag type;
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/* Input fields: */
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struct PlannerInfo *root; /* Planner's infrastructure */
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Oid funcid; /* function we are inquiring about */
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Node *node; /* parse node invoking function */
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int indexarg; /* index of function arg matching indexcol */
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struct IndexOptInfo *index; /* planner's info about target index */
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int indexcol; /* index of target index column (0-based) */
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Oid opfamily; /* index column's operator family */
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Oid indexcollation; /* index column's collation */
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/* Output fields: */
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bool lossy; /* set to false if index condition is an exact
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* equivalent of the function call */
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} SupportRequestIndexCondition;
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#endif /* SUPPORTNODES_H */
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