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Date: Tue, 28 Apr 2015 14:54:47 -0400
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 <CABWqe2ZckMb6_w46iLec8+Fqr-mL2w4FrwL-RSDmHhS0L5g6_A@mail.gmail.com>
Subject: Re: Leader election duration
From: Camille Fournier <camille@apache.org>
To: "user@zookeeper.apache.org" <user@zookeeper.apache.org>
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Just out of curiosity, if you start the 5 node cluster up with only 3 of
the nodes to begin with (like, config 5, but only bring up 3 processes),
does it speed up the leader election or is it still slow?

C

On Tue, Apr 28, 2015 at 1:41 PM, Karol Dudzinski <karoldudzinski@gmail.com>
wrote:

> Hi,
>
> We're seeing some rather strange leader election in one of our clusters.
> The duration reported by the "FOLLOWING - LEADER ELECTION TOOK" log line
> (and equivalent for the leader) seems to vary hugely.  During one rolling
> reboot, I saw the number reported as small as 39ms and as large as 57
> seconds (difference in units is not a typo).  The average is just about 10
> seconds and std dev also about 10 seconds.  So the time taken is not only
> quite large, it's also very variable.
>
> We have other clusters but the average election time in those is in the
> hundreds of millis with std dev in a similar ballpark.  I guess one
> difference is the "slow" cluster is 5 participants while the others are 3,
> which may be a factor but I wouldn't expect it to make two orders of
> magnitude difference!
>
> So my question is, what factors contribute to the election time reported
> by these log lines? And what can we do to speed this up?
>
> As far as I understand from logs and a quick browse through the code that
> time is the time to select a leader.  Syncing up to the leader happens
> after that.  The syncing part I can understand will vary depending on load
> but I don't see why selecting the leader would.
>
> Thanks,
> Karol

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