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From Michi Mutsuzaki <mi...@cs.stanford.edu>
Subject Re: Zookeeper delay to reconnect
Date Thu, 27 Sep 2012 21:28:24 GMT
Hi Sergei,

Your suggestion sounds reasonable to me. I think the sleep was added
so that the client doesn't spin when the entire zookeeper is down. The
client could try to connect to each server without sleep, and sleep
for 1 second only after failing to connect to all the servers in the
cluster.

Thanks!
--Michi

On Thu, Sep 27, 2012 at 1:34 PM, Sergei Babovich
<sbabovich@demandware.com> wrote:
> Hi,
> Zookeeper implements a delay of up to 1 second before trying to reconnect.
>
> ClientCnxn$SendThread
>         @Override
>         public void run() {
>             ...
>             while (state.isAlive()) {
>                 try {
>                     if (!clientCnxnSocket.isConnected()) {
>                         if(!isFirstConnect){
>                             try {
>                                 Thread.sleep(r.nextInt(1000));
>                             } catch (InterruptedException e) {
>                                 LOG.warn("Unexpected exception", e);
>                             }
>
> This creates "outages" (even with simple retry on ConnectionLoss) up to 1s
> even with perfectly healthy cluster like in scenario of rolling restart. In
> our scenario it might be a problem under high load creating a spike in a
> number of requests waiting on zk operation.
> Would it be a better strategy to perform reconnect attempt immediately at
> least one time? Or there is more to it?

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