Jordan Zimmerman created ZOOKEEPER-2163:
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Summary: 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
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).
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