ConsumerGroup crazy very slow, if pass topic as string

[darky]

Bug Report

Environment

• Node version: 9.6.1
• Kafka-node version: 2.4.1
• Kafka version: 0.9

Include Sample Code to reproduce behavior

// All ok
var consumerGroup = new ConsumerGroup(options, ['RebalanceTopic');

// Crazy very slow
var consumerGroup = new ConsumerGroup(options, 'RebalanceTopic');

[aikar]

There is something else at play and not what you think it is.

lodash's isString is not going to be slow, nor would it have a long running impact on the overall runtime.

This code is only ran during consumer creation.

[darky]

Sorry, I mean receiving messages process.

var consumerGroup = new ConsumerGroup(options, ['RebalanceTopic']);
consumerGroup.on("message", m => {
  // this call so fast
});

var consumerGroup = new ConsumerGroup(options, 'RebalanceTopic');
consumerGroup.on("message", m => {
  // this almost not call, very poor performance
})

[davidqhr]

I met this. Thanks @darky

[hyperlink]

The string gets turned into an array that's the only difference between the two. https://github.com/SOHU-Co/kafka-node/blob/master/lib/consumerGroup.js#L95

Do you have some sample code to demonstrate this issue?

[darky]

I don't understand, how it occured, but code smell bad little bit. No need to mutate parameters, otherwise need directly assign:

this.topics = _.isString(topics) ? [topics] : topics;

[aikar]

The only way this code can have a problem is if you found a performance bug in v8, which I doubt that such a simple operation of wrapping a string in an array would be an issue. It would be chaos on the internet if there was since this is an extremely common pattern.

[aikar]

Your issue has nothing to do with string vs array. You're going to need to give hyperlink more code / details / debug logs.