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Date: Wed, 29 Jul 2015 11:21:55 -0500
From: Jordan Zimmerman <jordan@jordanzimmerman.com>
To: user@zookeeper.apache.org, Prabhjot Bharaj <prabhbharaj@gmail.com>,
 dev@zookeeper.apache.org
Message-ID: <etPan.55b8fda3.429631e0.15d@Jordans-MacBook-Pro.local>
In-Reply-To: 
 <CANXk_5m_t7wiEsBDjtnGPH1FiVKPEDb+xX2spKhc1RyE9mi8jw@mail.gmail.com>
References: 
 <CANXk_5m_t7wiEsBDjtnGPH1FiVKPEDb+xX2spKhc1RyE9mi8jw@mail.gmail.com>
Subject: Re: Corner case in Ephemeral-sequential node creation
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Here=E2=80=99s the comment from Curator that explains it and how Curator =
works around it:

=22It turns out there is an edge case that exists when creating sequentia=
l-ephemeral nodes. The creation can succeed on the server, but the server=
 can crash before the created node name is returned to the client. Howeve=
r, the ZK session is still valid so the ephemeral node is not deleted. Th=
us, there is no way for the client to determine what node was created for=
 them.

Even without sequential-ephemeral, however, the create can succeed on the=
 sever but the client (for various reasons) will not know it.

Putting the create builder into protection mode works around this. The na=
me of the node that is created is prefixed with a GUID. If node creation =
fails the normal retry mechanism will occur. On the retry, the parent pat=
h is first searched for a node that has the GUID in it. If that node is f=
ound, it is assumed to be the lost node that was successfully created on =
the first try and is returned to the caller.=22


On July 29, 2015 at 11:19:37 AM, Prabhjot Bharaj (prabhbharaj=40gmail.com=
) wrote:

Hello folks, =20

I was going through this blog : =20
http://blog.cloudera.com/blog/2013/05/zookeeper-made-simpler/ (it is 2+ =20
years old) =20

In the second paragraph of the 'Recipes' section, there is a sentence:- =20


*New users of ZooKeeper will not know that there is an edge case in =20
ephemeral-sequential node creation that requires you to put a special =20
=E2=80=9Cmarker=E2=80=9D in the node=E2=80=99s name so that you can searc=
h for the created node if =20
an I/O failure occurs. This is but one of many edge cases that are not ye=
t =20
well documented.* =20

I would request you to explain this corner case here, as I haven't =20
considered this corner case anytime in my code. =20

Regards, =20
prabcs =20

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