GitHub user tillrohrmann opened a pull request:
https://github.com/apache/flink/pull/3940
[backport 1.3] [FLINK-6612] Allow ZooKeeperStateHandleStore to lock created
ZNodes
Backport of #3939 onto the `release-1.3` branch.
In order to guard against deletions of ZooKeeper nodes which are still
being used
by a different ZooKeeperStateHandleStore, we have to introduce a locking
mechanism.
Only after all ZooKeeperStateHandleStores have released their lock, the
ZNode is
allowed to be deleted.
THe locking mechanism is implemented via ephemeral child nodes of the
respective
ZooKeeper node. Whenever a ZooKeeperStateHandleStore wants to lock a ZNode,
thus,
protecting it from being deleted, it creates an ephemeral child node. The
node's
name is unique to the ZooKeeperStateHandleStore instance. The delete
operations
will then only delete the node if it does not have any children associated.
In order to guard against oprhaned lock nodes, they are created as
ephemeral nodes.
This means that they will be deleted by ZooKeeper once the connection of the
ZooKeeper client which created the node timed out.
You can merge this pull request into a Git repository by running:
$ git pull https://github.com/tillrohrmann/flink
addZooKeeperRefCountingBackport
Alternatively you can review and apply these changes as the patch at:
https://github.com/apache/flink/pull/3940.patch
To close this pull request, make a commit to your master/trunk branch
with (at least) the following in the commit message:
This closes #3940
----
commit ccb3ac8f2b64a357275d2967fcd440947becd272
Author: Till Rohrmann <[email protected]>
Date: 2017-05-17T12:52:04Z
[FLINK-6612] Allow ZooKeeperStateHandleStore to lock created ZNodes
In order to guard against deletions of ZooKeeper nodes which are still
being used
by a different ZooKeeperStateHandleStore, we have to introduce a locking
mechanism.
Only after all ZooKeeperStateHandleStores have released their lock, the
ZNode is
allowed to be deleted.
THe locking mechanism is implemented via ephemeral child nodes of the
respective
ZooKeeper node. Whenever a ZooKeeperStateHandleStore wants to lock a ZNode,
thus,
protecting it from being deleted, it creates an ephemeral child node. The
node's
name is unique to the ZooKeeperStateHandleStore instance. The delete
operations
will then only delete the node if it does not have any children associated.
In order to guard against oprhaned lock nodes, they are created as
ephemeral nodes.
This means that they will be deleted by ZooKeeper once the connection of the
ZooKeeper client which created the node timed out.
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