Function _reduceEdgeCount

src/execution_plan/optimizations/reduce_count.c:157–221

}

void _reduceEdgeCount(ExecutionPlan *plan) {
	// we'll only modify execution plan if it is structured as follows:
	// "Full Scan -> Conditional Traverse -> Aggregate -> Results"
	OpBase *opScan;
	OpBase *opTraverse;
	OpResult *opResult;
	OpAggregate *opAggregate;

	// see if execution-plan matches the pattern:
	// "Full Scan -> Conditional Traverse -> Aggregate -> Results"
	// if that's not the case, simply return without making any modifications
	if(!_identifyEdgeCountPattern(plan->root, &opResult, &opAggregate,
				&opTraverse, &opScan)) return;

	// user is trying to count edges (either in total or of specific types)
	// in the graph. optimize by skipping Scan, Traverse and Aggregate
	Graph *g = QueryCtx_GetGraph();
	SIValue edgeCount = SI_LongVal(0);

	// if type is specified, count only labeled entities
	OpCondTraverse *condTraverse = (OpCondTraverse *)opTraverse;
	// the traversal op doesn't contain information about the traversed edge,
	// cannot apply optimization
	if(!condTraverse->edge_ctx) return;

	uint relationCount = array_len(condTraverse->edge_ctx->edgeRelationTypes);

	uint64_t edges = 0;
	for(uint i = 0; i < relationCount; i++) {
		int relType = condTraverse->edge_ctx->edgeRelationTypes[i];
		switch(relType) {
			case GRAPH_NO_RELATION:
				// should be the only relationship type mentioned, -[]->
				edges = Graph_EdgeCount(g);
				break;
			case GRAPH_UNKNOWN_RELATION:
				// no change to current count, -[:none_existing]->
				break;
			default:
				edges += Graph_RelationEdgeCount(g, relType);
		}
	}
	edgeCount = SI_LongVal(edges);

	// construct a constant expression, used by a new projection operation
	AR_ExpNode *exp = AR_EXP_NewConstOperandNode(edgeCount);
	// 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 *)opTraverse);