Function GetCachedPlan

src/backend/utils/cache/plancache.c:1248–1358

* GetCachedPlan: get a cached plan from a CachedPlanSource. * * This function hides the logic that decides whether to use a generic * plan or a custom plan for the given parameters: the caller does not know * which it will get. * * On return, the plan is valid and we have sufficient locks to begin * execution. * * On return, the refcount of the plan has been incremented; a later * Releas

 * therefore also forces the plan to be re-planned on next call.
 */
CachedPlan *
GetCachedPlan(CachedPlanSource *plansource, ParamListInfo boundParams,
			  ResourceOwner owner, QueryEnvironment *queryEnv, IntoClause *intoClause)
{
	CachedPlan *plan = NULL;
	List	   *qlist;
	bool		customplan;

	/* Assert caller is doing things in a sane order */
	Assert(plansource->magic == CACHEDPLANSOURCE_MAGIC);
	Assert(plansource->is_complete);
	/* This seems worth a real test, though */
	if (owner && !plansource->is_saved)
		elog(ERROR, "cannot apply ResourceOwner to non-saved cached plan");

	/* Make sure the querytree list is valid and we have parse-time locks */
	qlist = RevalidateCachedQuery(plansource, queryEnv, intoClause);

	/* Decide whether to use a custom plan */
	customplan = choose_custom_plan(plansource, boundParams, intoClause);

	if (!customplan)
	{
		if (CheckCachedPlan(plansource))
		{
			/* We want a generic plan, and we already have a valid one */
			plan = plansource->gplan;
			Assert(plan->magic == CACHEDPLAN_MAGIC);
		}
		else
		{
			/* Build a new generic plan */
			plan = BuildCachedPlan(plansource, qlist, NULL, queryEnv, NULL);
			/* Just make real sure plansource->gplan is clear */
			ReleaseGenericPlan(plansource);
			/* Link the new generic plan into the plansource */
			plansource->gplan = plan;
			plan->refcount++;
			/* Immediately reparent into appropriate context */
			if (plansource->is_saved)
			{
				/* saved plans all live under CacheMemoryContext */
				MemoryContextSetParent(plan->context, CacheMemoryContext);
				plan->is_saved = true;
			}
			else
			{
				/* otherwise, it should be a sibling of the plansource */
				MemoryContextSetParent(plan->context,
									   MemoryContextGetParent(plansource->context));
			}
			/* Update generic_cost whenever we make a new generic plan */
			plansource->generic_cost = cached_plan_cost(plan, false);

			/*
			 * If, based on the now-known value of generic_cost, we'd not have
			 * chosen to use a generic plan, then forget it and make a custom
			 * plan.  This is a bit of a wart but is necessary to avoid a