Introduce field tracking cached plan type in PlannedStmt

PlannedStmt gains a new field, called CachedPlanType, able to track if a
given plan tree originates from the cache and if we are dealing with a
generic or custom cached plan.

This field can be used for monitoring or statistical purposes, in the
executor hooks, for example, based on the planned statement attached to
a QueryDesc.  A patch is under discussion for pg_stat_statements to
provide an equivalent of the counters in pg_prepared_statements for
custom and generic plans, to provide a more global view of such data, as
this data is now restricted to the current session.

The concept introduced in this commit is useful on its own, and has been
extracted from a larger patch by the same author.

Author: Sami Imseih <samimseih@gmail.com>
Reviewed-by: Andrei Lepikhov <lepihov@gmail.com>
Reviewed-by: Michael Paquier <michael@paquier.xyz>
Discussion: https://postgr.es/m/CAA5RZ0uFw8Y9GCFvafhC=OA8NnMqVZyzXPfv_EePOt+iv1T-qQ@mail.gmail.com

1 files changed, 17 insertions, 0 deletions

diff --git a/src/include/nodes/plannodes.h b/src/include/nodes/plannodes.h
index 4f59e30d62d..46e2e09ea35 100644
--- a/src/include/nodes/plannodes.h
+++ b/src/include/nodes/plannodes.h
@@ -29,6 +29,20 @@
  */
 
 /* ----------------
+ *		CachedPlanType
+ *
+ * CachedPlanType identifies whether a PlannedStmt is a cached plan, and if
+ * so, whether it is generic or custom.
+ * ----------------
+ */
+typedef enum CachedPlanType
+{
+	PLAN_CACHE_NONE = 0,		/* Not a cached plan */
+	PLAN_CACHE_GENERIC,			/* Generic cached plan */
+	PLAN_CACHE_CUSTOM,			/* Custom cached plan */
+} CachedPlanType;
+
+/* ----------------
  *		PlannedStmt node
  *
  * The output of the planner is a Plan tree headed by a PlannedStmt node.
@@ -58,6 +72,9 @@ typedef struct PlannedStmt
 	/* plan identifier (can be set by plugins) */
 	int64		planId;
 
+	/* type of cached plan */
+	CachedPlanType cached_plan_type;
+
 	/* is it insert|update|delete|merge RETURNING? */
 	bool		hasReturning;