plancache.h

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/*-------------------------------------------------------------------------
 *
 * plancache.h
 *    Plan cache definitions.
 *
 * See plancache.c for comments.
 *
 * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * src/include/utils/plancache.h
 *
 *-------------------------------------------------------------------------
 */
#ifndef PLANCACHE_H
#define PLANCACHE_H

#include "access/tupdesc.h"
#include "lib/ilist.h"
#include "nodes/params.h"
#include "tcop/cmdtag.h"
#include "utils/queryenvironment.h"
#include "utils/resowner.h"


/* Forward declaration, to avoid including parsenodes.h here */
struct RawStmt;

/* possible values for plan_cache_mode */
typedef enum
{
    PLAN_CACHE_MODE_AUTO,
    PLAN_CACHE_MODE_FORCE_GENERIC_PLAN,
    PLAN_CACHE_MODE_FORCE_CUSTOM_PLAN
}           PlanCacheMode;

/* GUC parameter */
extern int  plan_cache_mode;

#define CACHEDPLANSOURCE_MAGIC      195726186
#define CACHEDPLAN_MAGIC            953717834
#define CACHEDEXPR_MAGIC            838275847

/*
 * CachedPlanSource (which might better have been called CachedQuery)
 * represents a SQL query that we expect to use multiple times.  It stores
 * the query source text, the raw parse tree, and the analyzed-and-rewritten
 * query tree, as well as adjunct data.  Cache invalidation can happen as a
 * result of DDL affecting objects used by the query.  In that case we discard
 * the analyzed-and-rewritten query tree, and rebuild it when next needed.
 *
 * An actual execution plan, represented by CachedPlan, is derived from the
 * CachedPlanSource when we need to execute the query.  The plan could be
 * either generic (usable with any set of plan parameters) or custom (for a
 * specific set of parameters).  plancache.c contains the logic that decides
 * which way to do it for any particular execution.  If we are using a generic
 * cached plan then it is meant to be re-used across multiple executions, so
 * callers must always treat CachedPlans as read-only.
 *
 * Once successfully built and "saved", CachedPlanSources typically live
 * for the life of the backend, although they can be dropped explicitly.
 * CachedPlans are reference-counted and go away automatically when the last
 * reference is dropped.  A CachedPlan can outlive the CachedPlanSource it
 * was created from.
 *
 * An "unsaved" CachedPlanSource can be used for generating plans, but it
 * lives in transient storage and will not be updated in response to sinval
 * events.
 *
 * CachedPlans made from saved CachedPlanSources are likewise in permanent
 * storage, so to avoid memory leaks, the reference-counted references to them
 * must be held in permanent data structures or ResourceOwners.  CachedPlans
 * made from unsaved CachedPlanSources are in children of the caller's
 * memory context, so references to them should not be longer-lived than
 * that context.  (Reference counting is somewhat pro forma in that case,
 * though it may be useful if the CachedPlan can be discarded early.)
 *
 * A CachedPlanSource has two associated memory contexts: one that holds the
 * struct itself, the query source text and the raw parse tree, and another
 * context that holds the rewritten query tree and associated data.  This
 * allows the query tree to be discarded easily when it is invalidated.
 *
 * Some callers wish to use the CachedPlan API even with one-shot queries
 * that have no reason to be saved at all.  We therefore support a "oneshot"
 * variant that does no data copying or invalidation checking.  In this case
 * there are no separate memory contexts: the CachedPlanSource struct and
 * all subsidiary data live in the caller's CurrentMemoryContext, and there
 * is no way to free memory short of clearing that entire context.  A oneshot
 * plan is always treated as unsaved.
 *
 * Note: the string referenced by commandTag is not subsidiary storage;
 * it is assumed to be a compile-time-constant string.  As with portals,
 * commandTag shall be NULL if and only if the original query string (before
 * rewriting) was an empty string.
 */
typedef struct CachedPlanSource
{
    int         magic;          /* should equal CACHEDPLANSOURCE_MAGIC */
    struct RawStmt *raw_parse_tree; /* output of raw_parser(), or NULL */
    const char *query_string;   /* source text of query */
    CommandTag  commandTag;     /* 'nuff said */
    Oid        *param_types;    /* array of parameter type OIDs, or NULL */
    int         num_params;     /* length of param_types array */
    ParserSetupHook parserSetup;    /* alternative parameter spec method */
    void       *parserSetupArg;
    int         cursor_options; /* cursor options used for planning */
    bool        fixed_result;   /* disallow change in result tupdesc? */
    TupleDesc   resultDesc;     /* result type; NULL = doesn't return tuples */
    MemoryContext context;      /* memory context holding all above */
    /* These fields describe the current analyzed-and-rewritten query tree: */
    List       *query_list;     /* list of Query nodes, or NIL if not valid */
    List       *relationOids;   /* OIDs of relations the queries depend on */
    List       *invalItems;     /* other dependencies, as PlanInvalItems */
    struct OverrideSearchPath *search_path; /* search_path used for parsing
                                             * and planning */
    MemoryContext query_context;    /* context holding the above, or NULL */
    Oid         rewriteRoleId;  /* Role ID we did rewriting for */
    bool        rewriteRowSecurity; /* row_security used during rewrite */
    bool        dependsOnRLS;   /* is rewritten query specific to the above? */
    /* If we have a generic plan, this is a reference-counted link to it: */
    struct CachedPlan *gplan;   /* generic plan, or NULL if not valid */
    /* Some state flags: */
    bool        is_oneshot;     /* is it a "oneshot" plan? */
    bool        is_complete;    /* has CompleteCachedPlan been done? */
    bool        is_saved;       /* has CachedPlanSource been "saved"? */
    bool        is_valid;       /* is the query_list currently valid? */
    int         generation;     /* increments each time we create a plan */
    /* If CachedPlanSource has been saved, it is a member of a global list */
    dlist_node  node;           /* list link, if is_saved */
    /* State kept to help decide whether to use custom or generic plans: */
    double      generic_cost;   /* cost of generic plan, or -1 if not known */
    double      total_custom_cost;  /* total cost of custom plans so far */
    int64       num_custom_plans;   /* # of custom plans included in total */
    int64       num_generic_plans;  /* # of generic plans */
} CachedPlanSource;

/*
 * CachedPlan represents an execution plan derived from a CachedPlanSource.
 * The reference count includes both the link from the parent CachedPlanSource
 * (if any), and any active plan executions, so the plan can be discarded
 * exactly when refcount goes to zero.  Both the struct itself and the
 * subsidiary data live in the context denoted by the context field.
 * This makes it easy to free a no-longer-needed cached plan.  (However,
 * if is_oneshot is true, the context does not belong solely to the CachedPlan
 * so no freeing is possible.)
 */
typedef struct CachedPlan
{
    int         magic;          /* should equal CACHEDPLAN_MAGIC */
    List       *stmt_list;      /* list of PlannedStmts */
    bool        is_oneshot;     /* is it a "oneshot" plan? */
    bool        is_saved;       /* is CachedPlan in a long-lived context? */
    bool        is_valid;       /* is the stmt_list currently valid? */
    Oid         planRoleId;     /* Role ID the plan was created for */
    bool        dependsOnRole;  /* is plan specific to that role? */
    TransactionId saved_xmin;   /* if valid, replan when TransactionXmin
                                 * changes from this value */
    int         generation;     /* parent's generation number for this plan */
    int         refcount;       /* count of live references to this struct */
    MemoryContext context;      /* context containing this CachedPlan */
} CachedPlan;

/*
 * CachedExpression is a low-overhead mechanism for caching the planned form
 * of standalone scalar expressions.  While such expressions are not usually
 * subject to cache invalidation events, that can happen, for example because
 * of replacement of a SQL function that was inlined into the expression.
 * The plancache takes care of storing the expression tree and marking it
 * invalid if a cache invalidation occurs, but the caller must notice the
 * !is_valid status and discard the obsolete expression without reusing it.
 * We do not store the original parse tree, only the planned expression;
 * this is an optimization based on the assumption that we usually will not
 * need to replan for the life of the session.
 */
typedef struct CachedExpression
{
    int         magic;          /* should equal CACHEDEXPR_MAGIC */
    Node       *expr;           /* planned form of expression */
    bool        is_valid;       /* is the expression still valid? */
    /* remaining fields should be treated as private to plancache.c: */
    List       *relationOids;   /* OIDs of relations the expr depends on */
    List       *invalItems;     /* other dependencies, as PlanInvalItems */
    MemoryContext context;      /* context containing this CachedExpression */
    dlist_node  node;           /* link in global list of CachedExpressions */
} CachedExpression;


extern void InitPlanCache(void);
extern void ResetPlanCache(void);

extern CachedPlanSource *CreateCachedPlan(struct RawStmt *raw_parse_tree,
                                          const char *query_string,
                                          CommandTag commandTag);
extern CachedPlanSource *CreateOneShotCachedPlan(struct RawStmt *raw_parse_tree,
                                                 const char *query_string,
                                                 CommandTag commandTag);
extern void CompleteCachedPlan(CachedPlanSource *plansource,
                               List *querytree_list,
                               MemoryContext querytree_context,
                               Oid *param_types,
                               int num_params,
                               ParserSetupHook parserSetup,
                               void *parserSetupArg,
                               int cursor_options,
                               bool fixed_result);

extern void SaveCachedPlan(CachedPlanSource *plansource);
extern void DropCachedPlan(CachedPlanSource *plansource);

extern void CachedPlanSetParentContext(CachedPlanSource *plansource,
                                       MemoryContext newcontext);

extern CachedPlanSource *CopyCachedPlan(CachedPlanSource *plansource);

extern bool CachedPlanIsValid(CachedPlanSource *plansource);

extern List *CachedPlanGetTargetList(CachedPlanSource *plansource,
                                     QueryEnvironment *queryEnv);

extern CachedPlan *GetCachedPlan(CachedPlanSource *plansource,
                                 ParamListInfo boundParams,
                                 ResourceOwner owner,
                                 QueryEnvironment *queryEnv);
extern void ReleaseCachedPlan(CachedPlan *plan, ResourceOwner owner);

extern bool CachedPlanAllowsSimpleValidityCheck(CachedPlanSource *plansource,
                                                CachedPlan *plan,
                                                ResourceOwner owner);
extern bool CachedPlanIsSimplyValid(CachedPlanSource *plansource,
                                    CachedPlan *plan,
                                    ResourceOwner owner);

extern CachedExpression *GetCachedExpression(Node *expr);
extern void FreeCachedExpression(CachedExpression *cexpr);

#endif                          /* PLANCACHE_H */