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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (ZOOKEEPER-2163) Introduce new ZNode type: container
Date Tue, 19 May 2015 21:35:00 GMT

    [ https://issues.apache.org/jira/browse/ZOOKEEPER-2163?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14551274#comment-14551274

ASF GitHub Bot commented on ZOOKEEPER-2163:

GitHub user Randgalt opened a pull request:


    Container support

    Assuming that ZOOKEEPER-2163 is accepted, container node support has been added to Curator.
Also, all recipes that create parent nodes now create container nodes

You can merge this pull request into a Git repository by running:

    $ git pull https://github.com/apache/curator CURATOR-222

Alternatively you can review and apply these changes as the patch at:


To close this pull request, make a commit to your master/trunk branch
with (at least) the following in the commit message:

    This closes #79
commit 04ae8115512f03210cf930118788c67e433bd904
Author: randgalt <randgalt@apache.org>
Date:   2015-05-19T21:33:24Z

    Assuming that ZOOKEEPER-2163 is accepted, container node support has been added to Curator.
Also, all recipes that create parent nodes now create container nodes


> Introduce new ZNode type: container
> -----------------------------------
>                 Key: ZOOKEEPER-2163
>                 URL: https://issues.apache.org/jira/browse/ZOOKEEPER-2163
>             Project: ZooKeeper
>          Issue Type: New Feature
>          Components: c client, java client, server
>    Affects Versions: 3.5.0
>            Reporter: Jordan Zimmerman
>            Assignee: Jordan Zimmerman
>             Fix For: 3.6.0
>         Attachments: zookeeper-2163.3.patch, zookeeper-2163.5.patch, zookeeper-2163.6.patch,
> ============
> A recurring problem for ZooKeeper users is garbage collection of parent nodes. Many recipes
(e.g. locks, leaders, etc.) call for the creation of a parent node under which participants
create sequential nodes. When the participant is done, it deletes its node. In practice, the
ZooKeeper tree begins to fill up with orphaned parent nodes that are no longer needed. The
ZooKeeper APIs don’t provide a way to clean these. Over time, ZooKeeper can become unstable
due to the number of these nodes.
> ===================
> Apache Curator has a workaround solution for this by providing the Reaper class which
runs in the background looking for orphaned parent nodes and deleting them. This isn’t ideal
and it would be better if ZooKeeper supported this directly.
> =========
> ZOOKEEPER-723 and ZOOKEEPER-834 have been proposed to allow EPHEMERAL nodes to contain
child nodes. This is not optimum as EPHEMERALs are tied to a session and the general use case
of parent nodes is for PERSISTENT nodes. This proposal adds a new node type, CONTAINER. A
CONTAINER node is the same as a PERSISTENT node with the additional property that when its
last child is deleted, it is deleted (and CONTAINER nodes recursively up the tree are deleted
if empty).
> ================
> {code}
> while ( true) { // or some reasonable limit
>     try {
>         zk.create(path, ...);
>         break;
>     } catch ( KeeperException.NoNodeException e ) {
>         try {
>             zk.createContainer(containerPath, ...);
>         } catch ( KeeperException.NodeExistsException ignore) {
>        }
>     }
> }
> {code}

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