Add delay in option for a MOVED response

[ohadisraeli]

When a MOVED response is received from the server currently the client supports only the maxRedirections option.
Adding a delay option can prevent a ping pong effect until the cluster has the new sharding state stabilized.

I think that if we can have the MOVED response to be pushed to a delayed queue like the way some of the other errors are handled as seen below:

    if (errv[0] === 'MOVED' || errv[0] === 'ASK') {
        handlers[errv[0] === 'MOVED' ? 'moved' : 'ask'](errv[1], errv[2]);
    }
    else if (errv[0] === 'TRYAGAIN') {
        this.delayQueue.push('tryagain', handlers.tryagain, {
            timeout: this.options.retryDelayOnTryAgain
        });
    }

[luin]

Hi, I think cases are rare in which the delay option is useful because most commonly, the correct slot target will be returned together with the MOVED error so simply redirect the command to that target would be efficient. This process follows the official spec: https://redis.io/topics/cluster-spec#redirection-and-resharding.

However, I can see how the delay option helps for the cases you mentioned as it "can prevent a ping pong effect" but I'd like to understand your specific case and what would you use as the value of the option.

[ohadisraeli]

In our case, we are experiencing under load that we get a MOVED response but the other node has not been yet updated therefore it again redirects to the original node and therefore the ping pong effect. I was thinking of the ability to support a delay parameter. Maybe a constant small number such as 50 might do the trick (currently, we see that the message is sent in about 2ms)

[ohadisraeli]

Maybe the change that I have applied in my environment will help to get a better understanding, the original code is commented:

if (errv[0] === 'MOVED' || errv[0] === 'ASK') {
  // handlers[errv[0] === "MOVED" ? "moved" : "ask"](errv[1], errv[2]);
  this.delayQueue.push("moved",handlers.moved.bind(null, errv[1], errv[2]),
    {
      timeout: this.options.retryDelayOnMoved(this.options.maxRedirections + 1 - ttl.value)
    }
  );

[luin]

Closed via #1254