Function _reduceNodeCount

src/execution_plan/optimizations/reduce_count.c:79–124

}

bool _reduceNodeCount(ExecutionPlan *plan) {
	/* We'll only modify execution plan if it is structured as follows:
	 * "Scan -> Aggregate -> Results" */
	const char *label;
	OpBase *opScan;
	OpResult *opResult;
	OpAggregate *opAggregate;

	/* See if execution-plan matches the pattern:
	 * "Scan -> Aggregate -> Results".
	 * if that's not the case, simply return without making any modifications. */
	if(!_identifyNodeCountPattern(plan->root, &opResult, &opAggregate, &opScan, &label)) return false;

	/* User is trying to get total number of nodes in the graph
	 * optimize by skiping SCAN and AGGREGATE. */
	SIValue nodeCount;
	GraphContext *gc = QueryCtx_GetGraphCtx();

	// If label is specified, count only labeled entities.
	if(label) {
		Schema *s = GraphContext_GetSchema(gc, label, SCHEMA_NODE);
		if(s) nodeCount = SI_LongVal(Graph_LabeledNodeCount(gc->g, s->id));
		else nodeCount = SI_LongVal(0); // Specified Label doesn't exists.
	} else {
		nodeCount = SI_LongVal(Graph_NodeCount(gc->g));
	}

	// Construct a constant expression, used by a new projection operation
	AR_ExpNode *exp = AR_EXP_NewConstOperandNode(nodeCount);
	// The new expression must be aliased to populate the Record.
	exp->resolved_name = opAggregate->aggregate_exps[0]->resolved_name;
	AR_ExpNode **exps = array_new(AR_ExpNode *, 1);
	array_append(exps, exp);

	OpBase *opProject = NewProjectOp(opAggregate->op.plan, exps);

	// New execution plan: "Project -> Results"
	ExecutionPlan_RemoveOp(plan, opScan);
	OpBase_Free(opScan);

	ExecutionPlan_RemoveOp(plan, (OpBase *)opAggregate);
	OpBase_Free((OpBase *)opAggregate);

	ExecutionPlan_AddOp((OpBase *)opResult, opProject);
	return true;
}

/* Checks if execution plan solely performs edge count */
static bool _identifyEdgeCountPattern(OpBase *root, OpResult **opResult,