Redesign the plancache mechanism for more flexibility and efficiency.

Rewrite plancache.c so that a "cached plan" (which is rather a misnomer
at this point) can support generation of custom, parameter-value-dependent
plans, and can make an intelligent choice between using custom plans and
the traditional generic-plan approach.  The specific choice algorithm
implemented here can probably be improved in future, but this commit is
all about getting the mechanism in place, not the policy.

In addition, restructure the API to greatly reduce the amount of extraneous
data copying needed.  The main compromise needed to make that possible was
to split the initial creation of a CachedPlanSource into two steps.  It's
worth noting in particular that SPI_saveplan is now deprecated in favor of
SPI_keepplan, which accomplishes the same end result with zero data
copying, and no need to then spend even more cycles throwing away the
original SPIPlan.  The risk of long-term memory leaks while manipulating
SPIPlans has also been greatly reduced.  Most of this improvement is based
on use of the recently-added MemoryContextSetParent primitive.

2 files changed, 97 insertions, 60 deletions

diff --git a/src/include/utils/memutils.h b/src/include/utils/memutils.h
index 94c78289b6e..4796f5c7057 100644
--- a/src/include/utils/memutils.h
+++ b/src/include/utils/memutils.h
@@ -94,6 +94,7 @@ extern void MemoryContextSetParent(MemoryContext context,
 								   MemoryContext new_parent);
 extern Size GetMemoryChunkSpace(void *pointer);
 extern MemoryContext GetMemoryChunkContext(void *pointer);
+extern MemoryContext MemoryContextGetParent(MemoryContext context);
 extern bool MemoryContextIsEmpty(MemoryContext context);
 extern void MemoryContextStats(MemoryContext context);
 
diff --git a/src/include/utils/plancache.h b/src/include/utils/plancache.h
index b8639a59a0e..c8c27bbb207 100644
--- a/src/include/utils/plancache.h
+++ b/src/include/utils/plancache.h
@@ -18,26 +18,47 @@
 #include "access/tupdesc.h"
 #include "nodes/params.h"
 
+#define CACHEDPLANSOURCE_MAGIC		195726186
+#define CACHEDPLAN_MAGIC			953717834
+
 /*
- * CachedPlanSource represents the portion of a cached plan that persists
- * across invalidation/replan cycles.  It stores a raw parse tree (required),
- * the original source text (also required, as of 8.4), and adjunct data.
+ * 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.
  *
- * Normally, both the struct itself and the subsidiary data live in the
- * context denoted by the context field, while the linked-to CachedPlan, if
- * any, has its own context.  Thus an invalidated CachedPlan can be dropped
- * when no longer needed, and conversely a CachedPlanSource can be dropped
- * without worrying whether any portals depend on particular instances of
- * its plan.
+ * 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.
  *
- * But for entries created by FastCreateCachedPlan, the CachedPlanSource
- * and the initial version of the CachedPlan share the same memory context.
- * In this case, we treat the memory context as belonging to the CachedPlan.
- * The CachedPlanSource has an extra reference-counted link (orig_plan)
- * to the CachedPlan, and the memory context goes away when the CachedPlan's
- * reference count goes to zero.  This arrangement saves overhead for plans
- * that aren't expected to live long enough to need replanning, while not
- * losing any flexibility if a replan turns out to be necessary.
+ * 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.
  *
  * Note: the string referenced by commandTag is not subsidiary storage;
  * it is assumed to be a compile-time-constant string.	As with portals,
@@ -46,78 +67,93 @@
  */
 typedef struct CachedPlanSource
 {
+	int			magic;			/* should equal CACHEDPLANSOURCE_MAGIC */
 	Node	   *raw_parse_tree; /* output of raw_parser() */
-	char	   *query_string;	/* text of query (as of 8.4, never NULL) */
+	char	   *query_string;	/* source text of query */
 	const char *commandTag;		/* command tag (a constant!), or NULL */
 	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		fully_planned;	/* do we cache planner or rewriter output? */
 	bool		fixed_result;	/* disallow change in result tupdesc? */
-	struct OverrideSearchPath *search_path;		/* saved search_path */
-	int			generation;		/* counter, starting at 1, for replans */
 	TupleDesc	resultDesc;		/* result type; NULL = doesn't return tuples */
-	struct CachedPlan *plan;	/* link to plan, or NULL if not valid */
-	MemoryContext context;		/* context containing this CachedPlanSource */
-	struct CachedPlan *orig_plan;		/* link to plan owning my context */
+	struct OverrideSearchPath *search_path;		/* saved search_path */
+	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 */
+	MemoryContext query_context; /* context holding the above, or NULL */
+	/* 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_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 */
+	struct CachedPlanSource *next_saved;	/* list link, if so */
+	/* 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 the portion of a cached plan that is discarded when
- * invalidation occurs.  The reference count includes both the link(s) from the
- * parent CachedPlanSource, 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.
+ * 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.
  */
 typedef struct CachedPlan
 {
-	List	   *stmt_list;		/* list of statement or Query nodes */
-	bool		fully_planned;	/* do we cache planner or rewriter output? */
-	bool		dead;			/* if true, do not use */
+	int			magic;			/* should equal CACHEDPLAN_MAGIC */
+	List	   *stmt_list;		/* list of statement nodes (PlannedStmts
+								 * and bare utility statements) */
+	bool		is_saved;		/* is CachedPlan in a long-lived context? */
+	bool		is_valid;		/* is the stmt_list currently valid? */
 	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 */
-	int			generation;		/* counter, starting at 1, for replans */
 	MemoryContext context;		/* context containing this CachedPlan */
-	/* These fields are used only in the not-fully-planned case: */
-	List	   *relationOids;	/* OIDs of relations the stmts depend on */
-	List	   *invalItems;		/* other dependencies, as PlanInvalItems */
 } CachedPlan;
 
 
 extern void InitPlanCache(void);
+extern void ResetPlanCache(void);
+
 extern CachedPlanSource *CreateCachedPlan(Node *raw_parse_tree,
 				 const char *query_string,
-				 const char *commandTag,
-				 Oid *param_types,
-				 int num_params,
-				 int cursor_options,
-				 List *stmt_list,
-				 bool fully_planned,
-				 bool fixed_result);
-extern CachedPlanSource *FastCreateCachedPlan(Node *raw_parse_tree,
-					 char *query_string,
-					 const char *commandTag,
-					 Oid *param_types,
-					 int num_params,
-					 int cursor_options,
-					 List *stmt_list,
-					 bool fully_planned,
-					 bool fixed_result,
-					 MemoryContext context);
-extern void CachedPlanSetParserHook(CachedPlanSource *plansource,
+				 const char *commandTag);
+extern void CompleteCachedPlan(CachedPlanSource *plansource,
+						List *querytree_list,
+						MemoryContext querytree_context,
+						Oid *param_types,
+						int num_params,
 						ParserSetupHook parserSetup,
-						void *parserSetupArg);
+						void *parserSetupArg,
+						int cursor_options,
+						bool fixed_result);
+
+extern void SaveCachedPlan(CachedPlanSource *plansource);
 extern void DropCachedPlan(CachedPlanSource *plansource);
-extern CachedPlan *RevalidateCachedPlan(CachedPlanSource *plansource,
-					 bool useResOwner);
-extern void ReleaseCachedPlan(CachedPlan *plan, bool useResOwner);
+
+extern void CachedPlanSetParentContext(CachedPlanSource *plansource,
+									   MemoryContext newcontext);
+
+extern CachedPlanSource *CopyCachedPlan(CachedPlanSource *plansource);
+
 extern bool CachedPlanIsValid(CachedPlanSource *plansource);
-extern TupleDesc PlanCacheComputeResultDesc(List *stmt_list);
 
-extern void ResetPlanCache(void);
+extern List *CachedPlanGetTargetList(CachedPlanSource *plansource);
+
+extern CachedPlan *GetCachedPlan(CachedPlanSource *plansource,
+			  ParamListInfo boundParams,
+			  bool useResOwner);
+extern void ReleaseCachedPlan(CachedPlan *plan, bool useResOwner);
 
 #endif   /* PLANCACHE_H */