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https://issues.apache.org/jira/browse/ZOOKEEPER-1289?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13160434#comment-13160434
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Ted Dunning commented on ZOOKEEPER-1289:
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Yeah. And I really don't see a good way forward. The master knows that the
changes occurred in a multi, but I don't see how to notify the clients
correctly in the context of the current API.
The problems that I see are these:
a) ordinary watches have to work even if a node is updated in a multi.
Moreover, ordinary watches on one client have to work even if another client
wants a multi-watch.
b) what does it mean if I set a watch on one object and it and many others are
modified? What if one object is subject to multi-watching and another is
subject to normal watching and both are in a multi?
I suppose that you might imagine that the server always sends multi
notifications as multi's and never as individuals unless talking to a down-rev
client. Then the client would have to understand whether to deliver the
notifications one at a time (old style) or all at once (multi-style). The
client could have a magic switch that says to deliver multi's as multi's. But
that still leaves the problem of what happens in case (b).
> Multi Op Watch Events
> ---------------------
>
> Key: ZOOKEEPER-1289
> URL: https://issues.apache.org/jira/browse/ZOOKEEPER-1289
> Project: ZooKeeper
> Issue Type: New Feature
> Components: c client, java client, server
> Reporter: Marc Celani
>
> Caches built on top of zookeeper clients can become inconsistent because of
> lack of multi op watches. Our clients receive watch notifications for paths
> one at a time, and in their watch handling, invalidate the path in the cache.
> However, the cache now has an inconsistent view of zookeeper, since it is
> receiving the notifications one at a time. In general, the watch handling
> semantics do not conform with the idea of a multi op. If changes can be made
> to multiple paths atomically, all clients should be notified of that change
> atomically.
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