Function fake_outer_params

src/backend/executor/execUtils.c:1462–1498

* fake_outer_params * helper function to fake the nestloop's nestParams * so that prefetch inner or prefetch joinqual will * not encounter NULL pointer reference issue. It is * only invoked in ExecNestLoop and ExecPrefetchJoinQual * when the join is a nestloop join. */

 *   when the join is a nestloop join.
 */
void
fake_outer_params(JoinState *node)
{
	ExprContext    *econtext = node->ps.ps_ExprContext;
	PlanState      *inner = innerPlanState(node);
	TupleTableSlot *outerTupleSlot = econtext->ecxt_outertuple;
	NestLoop       *nl = (NestLoop *) (node->ps.plan);
	ListCell       *lc = NULL;

	/* only nestloop contains nestParams */
	Assert(IsA(node->ps.plan, NestLoop));

	/* econtext->ecxt_outertuple must have been set fakely. */
	Assert(outerTupleSlot != NULL);
	/*
	 * fetch the values of any outer Vars that must be passed to the
	 * inner scan, and store them in the appropriate PARAM_EXEC slots.
	 */
	foreach(lc, nl->nestParams)
	{
		NestLoopParam *nlp = (NestLoopParam *) lfirst(lc);
		int			paramno = nlp->paramno;
		ParamExecData *prm;

		prm = &(econtext->ecxt_param_exec_vals[paramno]);
		/* Param value should be an OUTER_VAR var */
		Assert(IsA(nlp->paramval, Var));
		Assert(nlp->paramval->varno == OUTER_VAR);
		Assert(nlp->paramval->varattno > 0);
		prm->value = slot_getattr(outerTupleSlot,
								  nlp->paramval->varattno,
								  &(prm->isnull));
		/* Flag parameter value as changed */
		inner->chgParam = bms_add_member(inner->chgParam,
										 paramno);
	}
}

/*
 * Prefetch JoinQual or NonJoinQual to prevent motion hazard.