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From Jordan Zimmerman <jor...@jordanzimmerman.com>
Subject Re: PathChildrenCache and event order
Date Sat, 21 Sep 2013 01:04:28 GMT
Assuming events come in order from ZK (which I believe they're supposed to), then PathChildrenCache
will report them in order. However, PathChildrenCache makes no guarantee of this. A deeper
point, though, is that you cannot get every event from ZooKeeper. As that same wiki says,
"you cannot reliably see every change that happens to a node in ZooKeeper". So, I think you'd
need to reconsider your algorithm regardless.

-JZ

On Sep 20, 2013, at 11:27 AM, Benjamin Jaton <bjaton@radiantlogic.com> wrote:

> Some configuration is stored in ZooKeeper and we are trying to keep a local copy on disk,
updated through events.
> 
> I think ZooKeeper guarantees some kind of ordering, especially this one:
> "The order of watch events from ZooKeeper corresponds to the order of the updates as
seen by the ZooKeeper service."
> Which I thought was my use case.
> 
> Thanks,
> Benjamin
> 
> 
> 
> On Thu, Sep 19, 2013 at 4:26 PM, Eric Tschetter <echeddar@gmail.com> wrote:
> Can you give some more insight into what end goal you are trying to achieve? 
> --Eric
> 
> 
> On Thursday, September 19, 2013, Eric Tschetter wrote:
> Benjamin,
> 
> That's not really possible.  Also, any protocol built around requiring them in order
is most likely going to have nasty corner cases in the face of network partitions and server
failures.
> 
> --Eric
> 
> On Thursday, September 19, 2013, Benjamin Jaton wrote:
> Hello,
> 
> I am trying to have PathChildrenCache send me create events in the same order the nodes
were created.
> Is that possible?
> 
> Attached is a simple example where I create node0, node1, node2, etc and I often get
the notification for node2 before node1, or the like.
> Note: PathChildrenCache is created with Executors.newSingleThreadExecutor().
> 
> Thanks!
> Benjamin
> 


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