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https://issues.apache.org/jira/browse/ZOOKEEPER-2163?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Michi Mutsuzaki reopened ZOOKEEPER-2163:
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[~rgs] could you address Rakesh's comment?
> 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: 3.5.1, 3.6.0
>
> Attachments: zookeeper-2163.10.patch, zookeeper-2163.11.patch,
> zookeeper-2163.12.patch, zookeeper-2163.13.patch, zookeeper-2163.14.patch,
> zookeeper-2163.3.patch, zookeeper-2163.5.patch, zookeeper-2163.6.patch,
> zookeeper-2163.7.patch, zookeeper-2163.8.patch, zookeeper-2163.9.patch
>
>
> BACKGROUND
> ============
> 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.
> CURRENT SOLUTIONS
> ===================
> 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.
> PROPOSAL
> =========
> 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).
> CANONICAL USAGE
> ================
> {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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