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From: Ted Dunning <ted.dunning@gmail.com>
Date: Sat, 28 May 2011 12:17:23 -0700
Message-ID: <BANLkTik_rG4Jf86As+qoWfXFaffECLJY4g@mail.gmail.com>
Subject: Re: Zookeeper in embedded mode
To: user@zookeeper.apache.org
Cc: zookeeper-user <zookeeper-user@hadoop.apache.org>
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There is a bit of a conundrum here.

Your problem is one of coordination.  In the Zookeeper world, it is common
to solve problems like this using ephemeral znodes to indicate that a server
is up.  Your problem is that you are trying to coordinate with the Zookeeper
process itself and don't have an external Zookeeper available to help you.

This problem of coordinating with the coordinator is exactly what makes
embedded use of Zookeeper somewhat problematic.  I have written, used and
tried to maintain applications that have embedded Zookeepers and this has
always been a problem.

In addition, using an embedded Zookeeper also leads to multi-master issues
because it is usually possible to invoke multiple copies of the program with
the embedded Zookeeper.  You don't usually want to hunt for a port number
because the ZK port should be a well-known thing (test cases are the major
exception) and you don't usually want to share some other invocations
embedded Zookeeper.  You also don't usually want Zookeeper to go down just
because of an application error.

All in all, I really prefer to have a separate Zookeeper service and avoid
embedded designs.  There is a small management overhead (just start it once
and arrange for restart on reboot ... it will run forever).


On Sat, May 28, 2011 at 10:18 AM, Avinash Lakshman <
avinash.lakshman@gmail.com> wrote:

> Hi All
>
> I am trying to run ZK in embedded mode. Basically I invoke
> QuorumPeerMain.main() on a separate thread. However is there a way to
> programmatically determine if the local server is ready to take write
> requests? I would like to on a separate thread create a Zookeeper instance
> and save some state. Currently I have a Thread.sleep(10seconds) to achieve
> what I want.
>
> Thanks in advance
> Avinash
>

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