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Subject: Re: Leader election in C# client
From: Flavio Junqueira <fpjunqueira@yahoo.com>
In-Reply-To: 
 <7B36F63619C46A49B86E0D5AB8CDD200617029B9@emea-tc2-mb02.internal.sungard.corp>
Date: Tue, 26 Nov 2013 10:09:38 +0000
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 <7B36F63619C46A49B86E0D5AB8CDD200617029B9@emea-tc2-mb02.internal.sungard.corp>
To: user@zookeeper.apache.org

Hi Ben,

I'm not familiar with the C# implementation, but I suspect that:

- The session id is indeed to be able to identify the znode in the case =
the client sees a connection loss event and reexecutes the create;
- The sequence number creates an order among the bidders so that when a =
master crashes (ephemeral znode goes away), not all clients are =
notified. This solves the herd effect problem: many nodes being notified =
upon a single znode going away.

-Flavio


On Nov 26, 2013, at 9:57 AM, <Ben.Young@sungard.com> wrote:

> Hi,
>=20
> I was looking at the leader election algorithm in the .NET client at =
https://github.com/ewhauser/zookeeper/blob/trunk/src/dotnet/ZooKeeperNet.R=
ecipes/LeaderElection.cs
>=20
> There is a point I don't understand and I was wondering if someone =
could clarify for me. The recipe creates ephemeral nodes of the form =
"election-<sessionid>-<sequentialid>", I think to be able to see if it =
has already created the node (perhaps due to a retry?). However, doesn't =
having the session id in the node name then throw out the sorting of the =
nodes in the next step, to find the previous node to watch? I'd have =
thought it would then be sorting by session id and not sequential id? =
Perhaps that doesn't matter as long as only one node gets picked?
>=20
> Thanks,
> Ben
>=20
> Ben Young . Senior Software Engineer . Adaptiv . Position, Risk & =
Operations . SunGard . Enterprise House, Histon, Cambridge, CB24 9ZR .  =
Tel +44 (0) 1223 266042 . ben.young@sungard.com . www.sungard.com
>=20
> =20
>=20
>=20
>=20