Does pubnub heartbeat interval has an impact on memory?

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I have implemented pubnub to create a socket connection for receiving real-time messages. There is one thing which I noticed in my developer tools is that - the pubnub heartbeat state shows pending for a particular interval, mostly between 4.3-5 min.

After going through their documents, I realised the timeout can be modified and the default value is 320 seconds. After implementing this feature for my website I can notice some lag, I am not sure if it is pubnub who is causing the issue.

Please let me understand the the idea behind the pending state. Also, if it has an impact on memory. If yes, then how is the impact related to increase or decrease in the heartbeat interval ?

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FYI, my pubnub settings only consist of publisher key, subscriber key, uuid and ssl (true)

heartbeat pubnub google-chrome-devtools ajax javascript
2 Answers

PubNub Subscribe Connection and Long Poll Cycle

You are seeing the heartbeat query param but that is not the "presence heartbeat" API. That is the subscribe long poll connection which will remain open until:

  • a message is published on one of the channels you are subscribed to
  • or, if no messages were published on one of the subscribe channel after 280s, the connection is closed (200 response with no messages) and the SDK will open a new subscribe connection.

PENDING Connection

PENDING just means the subscribe connection is Open and waiting for messages to be published. This is expected.

I highly recommend that you do not change this value unless there is a good reason. Did you make it longer or shorter?

  • Shorter long poll has little value and practically no harm, technically speaking, but will result in more subscribe/edge transactions.
  • Longer long poll has an actual technical downside in that your client will disconnect after the 280s expiration but will not reconnect until the end of the new custom expiration time that you set for the client.

The only time you should set the value shorter is if you have an ISP that proactively closes "idle" (pending) connections quicker than 280s. This is very rare but it does happen.

And you will likely see that the subscribe connection gets CANCELED. This happens when the client app changes its channel subscription list: subscribe to a new channel or unsubscribe from an existing channel.

No Impact on Memory

But you are asking if there is some sort of impact on memory. The answer to that is - it should NOT have a negative impact. If you follow Nicolas Fodor's answer/advice, you might be able to confirm that but 1000's of customers into this, we have not had any memory issues with our JavaScript SDK related to this. Just be sure you are using the latest version of our SDKs and report any bugs/issues you find to PubNub Support with full details.

Presence Heartbeat

One more thing about the heartbeat query param value - it typically defaults to 300 (seconds) which is only important when you are using PubNub Presence. If the PubNub server doesn't hear from a client within that 300 second (or whatever it is set to) period, a presence timeout event, on behalf of that client, is sent to anyone listening for presence events. A timeout is like a delayed leave event.

See also:

user_13422320

Simple way to find out would be to check performances under load testing before and after the parameter change and without changing any other parameter. If a cause is established you can then vary the parameter value to assess the elasticity of the side effect.

user_141261810
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