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From "Patrick Hunt (JIRA)" <j...@apache.org>
Subject [jira] Created: (ZOOKEEPER-520) add static/readonly client session type
Date Fri, 04 Sep 2009 00:07:57 GMT
add static/readonly client session type
---------------------------------------

                 Key: ZOOKEEPER-520
                 URL: https://issues.apache.org/jira/browse/ZOOKEEPER-520
             Project: Zookeeper
          Issue Type: New Feature
          Components: c client, java client
            Reporter: Patrick Hunt
             Fix For: 3.3.0


Occasionally people (typically ops) has asked for the ability to start a ZK client with a
hardcoded, local, non cluster based session. Meaning that you can bring up a particular client
with a hardcoded/readonly view of the ZK namespace even if the zk cluster is not available.
This seems useful for a few reasons:

1) unforseen problems - a client might be brought up and partial application service restored
even in the face of catastrophic cluster failure

2) testing - client could be brought up with a hardcoded configuration for testing purposes.
we might even be able to extend this idea over time to allow "simulated changes" ie - simulate
other clients making changes in the namespace, perhaps simulate changes in the state of the
cluster (testing state change is often hard for users of the client interface)

Seems like this shouldn't be too hard for us to add. The session could be established with
a URI for a local/remote file rather than a URI of the cluster servers. The client would essentially
read this file which would be a simple representation of the znode namespace.

/foo/bar "abc"
/foo/bar2 "def"
etc...

In the pure client readonly case this is simple. We might also want to allow writes to the
namespace (essentially back this with an in memory hash) for things like group membership
(so that the client continues to function).

Obv this wouldn't work in some cases, but it might work in many and would allow further options
for users wrt building a relable/recoverable service on top of ZK.


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