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From "Raul Gutierrez Segales (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (ZOOKEEPER-2163) Introduce new ZNode type: container
Date Thu, 07 May 2015 15:24:00 GMT

    [ https://issues.apache.org/jira/browse/ZOOKEEPER-2163?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14532847#comment-14532847

Raul Gutierrez Segales commented on ZOOKEEPER-2163:

If this would work, it reduce a lot of boilerplate and it actually makes sense. Great idea

> 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
> ============
> 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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