perf(core): Introduce decorator to report slow method calls (#17729)

packages/@n8n/db/src/repositories/workflow.repository.ts

@@ -20,6 +20,7 @@ import type {
 	ListQuery,
 } from '../entities/types-db';
 import { isStringArray } from '../utils/is-string-array';
+import { TimedQuery } from '../utils/timed-query';
 
 type ResourceType = 'folder' | 'workflow';
 
@@ -371,6 +372,7 @@ export class WorkflowRepository extends Repository<WorkflowEntity> {
 		});
 	}
 
+	@TimedQuery()
 	async getMany(workflowIds: string[], options: ListQuery.Options = {}) {
 		if (workflowIds.length === 0) {
 			return [];

packages/@n8n/db/src/utils/timed-query.ts

@@ -0,0 +1,26 @@
+import { Logger } from '@n8n/backend-common';
+import { Timed } from '@n8n/decorators';
+import { Container } from '@n8n/di';
+
+/**
+ * Decorator that warns when database queries exceed a duration threshold.
+ *
+ * For options, see `@n8n/decorators/src/timed.ts`.
+ *
+ * @example
+ * ```ts
+ * @Service()
+ * class UserRepository {
+ *   @TimedQuery()
+ *   async findUsers() {
+ *     // will log warning if execution takes > 100ms
+ *   }
+ *
+ *   @TimedQuery({ threshold: 50, logArgs: true })
+ *   async findUserById(id: string) {
+ *     // will log warning if execution takes >50ms, including args
+ *   }
+ * }
+ * ```
+ */
+export const TimedQuery = Timed(Container.get(Logger), 'Slow database query');

packages/@n8n/decorators/src/index.ts

@@ -9,3 +9,4 @@ export * from './pubsub';
 export { Redactable } from './redactable';
 export * from './shutdown';
 export * from './module/module-metadata';
+export { Timed, TimedOptions } from './timed';

packages/@n8n/decorators/src/timed.ts

@@ -0,0 +1,42 @@
+export interface TimedOptions {
+	/** Duration (in ms) above which to log a warning. Defaults to `100`. */
+	threshold?: number;
+	/** Whether to include method parameters in the log. Defaults to `false`. */
+	logArgs?: boolean;
+}
+
+interface Logger {
+	warn(message: string, meta?: object): void;
+}
+
+/**
+ * Factory to create decorators to warn when method calls exceed a duration threshold.
+ */
+export const Timed =
+	(logger: Logger, msg = 'Slow method call') =>
+	(options: TimedOptions = {}): MethodDecorator =>
+	(_target, propertyKey, descriptor: PropertyDescriptor) => {
+		const originalMethod = descriptor.value as (...args: unknown[]) => unknown;
+		const thresholdMs = options.threshold ?? 100;
+		const logArgs = options.logArgs ?? false;
+
+		descriptor.value = async function (...args: unknown[]) {
+			const methodName = `${this.constructor.name}.${String(propertyKey)}`;
+			const start = performance.now();
+			const result = await originalMethod.apply(this, args);
+			const durationMs = performance.now() - start;
+
+			if (durationMs > thresholdMs) {
+				logger.warn(msg, {
+					method: methodName,
+					durationMs: Math.round(durationMs),
+					thresholdMs,
+					params: logArgs ? args : '[hidden]',
+				});
+			}
+
+			return result;
+		};
+
+		return descriptor;
+	};