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From "Samuel Nelson (Jira)" <j...@apache.org>
Subject [jira] [Created] (ZOOKEEPER-3566) Send event zxid to watches
Date Wed, 02 Oct 2019 04:37:00 GMT
Samuel Nelson created ZOOKEEPER-3566:
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             Summary: Send event zxid to watches
                 Key: ZOOKEEPER-3566
                 URL: https://issues.apache.org/jira/browse/ZOOKEEPER-3566
             Project: ZooKeeper
          Issue Type: Improvement
          Components: server
            Reporter: Samuel Nelson


The zxid that triggered a watch should be sent to the watch because it's useful for ordering
events.

 

Use case:

I'm watching a znode and syncing its contents (and whether it has been deleted) to a third
system. Without zxid attached to events it makes it very difficult to maintain the order of
events as they happened in ZK.

 

For example if I modify node `/a/b/c` and then delete it soon after, we have two watch events,
but no reliable way to communicate to our third system that the modification happened before
the deletion. If we are given the zxid we can use that to order events.

 

Suggested implementation:

Change `IWatchManager#triggerWatch` to take another parameter `Long zxid`. Callers pass the
zxid of the event.

Add member `Long zxid` to `WatchedEvent`

 



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