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/*-------------------------------------------------------------------------
*
* plancache.h
* Plan cache definitions.
*
* See plancache.c for comments.
*
* Portions Copyright (c) 1996-2020, 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 */
int num_custom_plans; /* number of plans included in total */
} 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,
bool useResOwner,
QueryEnvironment *queryEnv);
extern void ReleaseCachedPlan(CachedPlan *plan, bool useResOwner);
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 */
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