[ZOOKEEPER-4472] Support persistent watchers removing individually

• Type: Improvement
• Status: Closed
• Priority: Blocker
• Resolution: Fixed
• Affects Version/s: 3.6.3, 3.7.0
• Fix Version/s: 3.9.0
• Component/s: server
• Labels: pull-request-available

Release Note

Previously, client has to resort to WatcherType::Any to remove persistent watches. It is enough if client attaches only one watch mode per path. But after ZOOKEEPER-4466, we start to support different watches on one path officially, it becomes a serious problem as there could be other watch modes on path being removeWatches. So we decide to add WatcherType::Persistent and WatcherType::PersistentRecursive to remove persistent watch and persistent recursive watch respectively. This way, users of client can remove their watch even if there are other watch modes on that path. Still, users have to ensure there are no watchers with same watch mode on that path. But it is a pure Java Client issue. See ZOOKEEPER-4625 for reference.

• Assignee: Kezhu Wang
• Reporter: Kezhu Wang
• Created: 21/Feb/22 05:09
• Updated: 04/Aug/23 11:28
• Resolved: 15/Jun/23 05:14

Description

Persistent watchers could only be removed with WatcherType.Any now. I think it is meaningful to remove them individually as they are by naming persistent and will not auto removed in server side.

Together with proposed solution from ZOOKEEPER-4466, it will be clear that ZooKeeper has four kind of watchers:

1. Standard data watcher(which includes data and exist watcher in client side).
2. Standard child watcher.
3. Persistent node watcher(aka. data and child watcher for node).
4. Persistent recursive watcher(aka. data watcher for node and its descendants).

See also ZOOKEEPER-4471

Issue Links

• relates to: ZOOKEEPER-4471 Remove WatcherType.Children break persistent watcher's child events
• relates to: ZOOKEEPER-4466 Support different watch modes on same path
• links to: GitHub Pull Request #2006