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From "Cantrell, Curtis" <Curtis.Cantr...@bkfs.com>
Subject RE: Curator PathChildrenCache sends delete events but no delete happened
Date Tue, 25 Oct 2016 13:17:59 GMT
I have also experienced 3 delete events in the last year when there were no actual deletes
in ZK.   I was using the delete events as a trigger to do an actual deletion in the system.
 Since we experienced false deletes, I had to rethink the way I was using the PathChildrenCache.

Thank you,
Curtis Cantrell


From: Benjamin Jaton [mailto:benjamin.jaton@gmail.com]
Sent: Monday, October 24, 2016 7:34 PM
To: user@curator.apache.org
Subject: Re: Curator PathChildrenCache sends delete events but no delete happened

Hi Cameron, thanks for your answer.
Yes I noticed that too, it seems to be coming from the ZK client layer.
I have tried to use the ZK Watcher API but I couldn't reproduce the issue when I was using
them.
I will have a look at how PathChildrenCache does it and keep you posted.
Thanks
Benjamin

On Mon, Oct 24, 2016 at 4:08 PM, Cameron McKenzie <mckenzie.cam@gmail.com<mailto:mckenzie.cam@gmail.com>>
wrote:
hey Benjamin,
I'm not aware of any such edge cases, but that does not mean that they don't exist. From the
log:

2016-10-24 15:52:43 DEBUG o.a.z.ClientCnxn:889 - Got WatchedEvent state:SyncConnected type:NodeDeleted
path:/benji2/123 for sessionid 0x20014cf3d480003

This is being logged by the Zookeeper client itself that Curator is using. So it doesn't appear
to be Curator inferring some sort of delete event. It looks like an explicit watched event
coming from Zookeeper.

cheers

On Tue, Oct 25, 2016 at 10:04 AM, Benjamin Jaton <benjamin.jaton@gmail.com<mailto:benjamin.jaton@gmail.com>>
wrote:
Hello,
I am using PathChildrenCache and I am receiving delete events even if there is no actual delete
in ZK. I printed the WatchedEvent details for 2 of those delete events (of the same node /benji2/123)
I received in the same JVM run:


2016-10-24 15:52:43 DEBUG o.a.z.ClientCnxn:889 - Got WatchedEvent state:SyncConnected type:NodeDeleted
path:/benji2/123 for sessionid 0x20014cf3d480003
[PathChildrenCacheListener] delete event for /benji2/123
PathChildrenCacheEvent{type=CHILD_REMOVED, data=ChildData{path='/benji2/123', stat=19808389169191,19808389169191,1477335789916,1477335789916,0,0,0,0,0,0,19808389169191
, data=[]}}
null
ChildData{path='/benji2/123', stat=19808389169191,19808389169191,1477335789916,1477335789916,0,0,0,0,0,0,19808389169191
, data=[]}
getAversion=0
2016-10-24 15:52:43 DEBUG o.a.z.ClientCnxn:867 - Got notification sessionid:0x20014cf3d480003
getCtime=1477335789916
getCversion=0
getCzxid=19808389169191
getMtime=1477335789916
2016-10-24 15:52:43 DEBUG o.a.z.ClientCnxn:889 - Got WatchedEvent state:SyncConnected type:NodeDeleted
path:/benji2 for sessionid 0x20014cf3d480003
getMzxid=19808389169191
getPzxid=19808389169191
getVersion=0

(...)

2016-10-24 15:58:06 DEBUG o.a.z.ClientCnxn:889 - Got WatchedEvent state:SyncConnected type:NodeDeleted
path:/benji2/123 for sessionid 0x20014cf3d480003
[PathChildrenCacheListener] delete event for /benji2/123
PathChildrenCacheEvent{type=CHILD_REMOVED, data=ChildData{path='/benji2/123', stat=19808389169191,19808389169191,1477335789916,1477335789916,0,0,0,0,0,0,19808389169191
, data=[]}}
null
2016-10-24 15:58:06 DEBUG o.a.z.ClientCnxn:867 - Got notification sessionid:0x20014cf3d480003
ChildData{path='/benji2/123', stat=19808389169191,19808389169191,1477335789916,1477335789916,0,0,0,0,0,0,19808389169191
, data=[]}
getAversion=0
getCtime=1477335789916
getCversion=0
getCzxid=19808389169191
getMtime=1477335789916
getMzxid=19808389169191
getPzxid=19808389169191
getVersion=0

Are there known edge cases where this can happen? Again there is no delete at all in ZK, I
verified the transaction log of ZooKeeper, no delete is present).
Thanks,
Benjamin


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