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From fengguang gong <gongfenggu...@icloud.com>
Subject Re: How to atomic execute getData and delete in distributed system
Date Mon, 16 Sep 2013 09:17:27 GMT
thanks very much wt:

Your answer definitely answer my interrogations !

fengguang
在 2013-9-16,下午4:05,Warren Turkal <wt@penguintechs.org> 写道:

> I must not understand your question fully as cases (1) and (2) look very
> similar. It looks like you are trying to provide "atomic" access to the
> data in both cases. It looks like case (2) is a special case of case (1) in
> that only one of the processes is allowed to access the node and delete it.
> 
> If my understanding above is correct, you may be able to do the following
> for case (1). You can make your processes coordinate by using a distributed
> lock (implemented using ZK) to guard access to the node. Once you have the
> lock, you can do whatever you want to the node without fear that others are
> acting on it. You can find example lock code in the ZK
> docs<http://zookeeper.apache.org/doc/r3.4.5/recipes.html#sc_recipes_Locks>or
> you could use the Curator
> lib <https://github.com/Netflix/curator> to implement the lock.
> 
> As for case (2), you don't need a lock since only one process is allowed to
> access it. You could create the node name with a pattern such that you know
> it should only be processed by process4. For example, you might have the
> following hierarchy of znodes:
> 
>   - /myapp
>   - /myapp/case1nodes
>   - /myapp/case2nodes
> 
> Process4 and your other processes would know that only process4 is allowed
> to process nodes in /myapp/case2nodes.
> 
> If you need to elect a process to be "process4", you can use ZK to
> implement an election (see this
> link<http://zookeeper.apache.org/doc/r3.4.5/recipes.html#sc_leaderElection>
> for
> a ZK recipe).
> 
> wt
> 
> 
> On Sun, Sep 15, 2013 at 10:27 PM, fengguang gong
> <gongfengguang@icloud.com>wrote:
> 
>> Hi all:
>> when a znode is updated, there are four processes(1.2.3.4)can access the
>> znode.
>> Two cases:
>> (1)what i need is that there is only one process execute getData and
>> delete atomically.
>> (2)what i need is that process4 execute getData and delete atomically.
>> In case (1), EPHEMERAL_SEQUENTIAL will be used.
>> In case (2), what should i do?


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