问题
We are using GraphQL Subscriptions and pubsub to subscribe to posts.
When more than 10 subscriptions occur we get the the node warning "MaxListenersExceededWarning: Possible EventEmitter memory leak detected."
Is it possible to raise the max listeners in the pubsub class?
The pubsub class is inside a separate module and looks like this:
import { PubSub } from 'graphql-subscriptions';
const pubsub = new PubSub();
export { pubsub };
The subscription server looks like this:
import { SubscriptionManager } from 'graphql-subscriptions';
import { createServer } from 'http';
import { SubscriptionServer } from 'subscriptions-transport-ws';
import { pubsub } from './subscriptions';
import executableSchema from './executableSchema';
const WS_PORT = 8080;
const websocketServer = createServer((request, response) => {
response.writeHead(404);
response.end();
});
websocketServer.listen(WS_PORT, () => console.log(
`Websocket Server is now running on http://localhost:${WS_PORT}`
));
const subscriptionManager = new SubscriptionManager({
schema: executableSchema,
pubsub: pubsub,
setupFunctions: {
newPost: (options, args) => {
return {
newPostChannel: {
filter: (post) => {
return args.publicationId === post.relatedPublication.id;
}
},
};
},
},
});
const subscriptionServer = new SubscriptionServer({
subscriptionManager: subscriptionManager
}, {
server: websocketServer,
path: '/',
});
export {
subscriptionServer,
};
回答1:
I wrote the original implementation of the graphql-subscriptions package you're using, so I can provide some context here.
The simple EventEmitter pubsub library included in graphql-subscriptions is only intended for demo purposes. EventEmitters don't really scale to large numbers, they're in-memory, and they'll only work as long as you have no more than a single server.
For anyone trying to run GraphQL subscriptions in production, I strongly recommend using a different system, for example Redis or MQTT through graphql-redis-subscriptions or graphql-mqtt-subscriptions. This will have the advantage of keeping the GraphQL server stateless (apart from the websockets) and thus easy to scale horizontally.
回答2:
Found out that you can change the max listeners in the event emitter of the pubsub instance, like so:
import { PubSub } from 'graphql-subscriptions';
const pubsub = new PubSub();
pubsub.ee.setMaxListeners(30); // raise max listeners in event emitter
export { pubsub };
来源:https://stackoverflow.com/questions/43752073/graphql-subscriptions-max-listeners-exceeded-warning