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From Michi Mutsuzaki <mi...@cs.stanford.edu>
Subject Re: Thread handling
Date Wed, 02 Apr 2014 07:20:33 GMT
It would be very difficult to preserve the request order when critical
threads re-spawn. Re-spawning threads works well in many applications,
but I don't think it's a good fit for ZooKeeper.

On Tue, Apr 1, 2014 at 9:57 PM, Rakesh R <rakeshr@huawei.com> wrote:
>
>>>> I prefer re-spawning the thread specifically because of the embedded situation.
> Actually I'd like to know the way embedding the ZK server. Does the application holds
the reference of ZooKeeper server, if yes, there is a way by checking ZooKeeperServer# isRunning().
> If not, it would be good to reach to a common understanding or agreement for the embedded
server approach. I could see ZOOKEEPER-1072 is open for discussion.
>
>
>>>> I mean ideally if we know how to resolve the issue we should just resolve
the issue instead of relying on an external system like monitoring.
> Actually this is again a debatable topic. But my opinion is, restarting the server would
be simple idea compare to pinpointing the actual cause and finding the remedies. Mostly this
would involves too much of tiny conditions and would introduce complexities. What do you say
?
>
>
> -Rakesh
>
> -----Original Message-----
> From: Asta, Greg [mailto:greg.asta@omnigon.com]
> Sent: 01 April 2014 21:31
> To: user@zookeeper.apache.org; michi@cs.stanford.edu; dev@zookeeper.apache.org
> Subject: RE: Thread handling
>
> I prefer re-spawning the thread specifically because of the embedded situation.   I mean
ideally if we know how to resolve the issue we should just resolve the issue instead of relying
on an external system like monitoring.
>
> -Greg
>
> -----Original Message-----
> From: mutsuzaki@gmail.com [mailto:mutsuzaki@gmail.com] On Behalf Of Michi Mutsuzaki
> Sent: Tuesday, April 01, 2014 5:22 AM
> To: dev@zookeeper.apache.org
> Cc: user@zookeeper.apache.org
> Subject: Re: Thread handling
>
> +1 for shutting down on a critical thread death.
>
> Does 'shutdown' mean calling System.exit or throwing some kind of exception? Some applications
use ZooKeeper embedded in their JVM, and they might not like ZooKeeper calling System.exit.
>
> --Michi
>
> On Mon, Mar 31, 2014 at 9:03 PM, Rakesh R <rakeshr@huawei.com> wrote:
>>>>> This is how I handle the critical threads in my client apps that use
Zookeeper.
>>>>> Keep a reference to the thread and periodically make sure it's still
alive and well - respawn it if it is not.
>>
>> Thanks Greg for the inputs. Please see ZK-1907, I've included an initial proposal
patch to kick start the discussions.
>> Another approach is simply shutdown if a critical thread dies, so the monitoring
tool can easily detect and take necessary actions. The proposed patch is based on this approach.
>>
>> -Rakesh
>>
>> -----Original Message-----
>> From: Asta, Greg [mailto:greg.asta@omnigon.com]
>> Sent: 31 March 2014 23:24
>> To: user@zookeeper.apache.org; dev@zookeeper.apache.org
>> Subject: RE: Thread handling
>>
>> " If we have a 'DeathWatcher 'or some other mechanism in place to monitor all the
critical threads. It can take a decision like - bring down the process if required, or shutdown
the quorumpeer and go for LE again etc.
>> Now the monitoring or management tool will knows about the situation and can act
upon.
>>
>> Appreciate any thoughts ?"
>>
>> This is how I handle the critical threads in my client apps that use Zookeeper. 
Keep a reference to the thread and periodically make sure it's still alive and well - respawn
it if it is not.
>>
>> Thanks,
>> Greg
>>
>>
>> -----Original Message-----
>> From: Rakesh R [mailto:rakeshr@huawei.com]
>> Sent: Thursday, March 27, 2014 10:39 AM
>> To: dev@zookeeper.apache.org; user@zookeeper.apache.org
>> Subject: Thread handling
>>
>> Hi All,
>>
>> Server has many critical threads running and co-ordinating each other like  RequestProcessor
chains et. When going through each threads, most of them having the similar structure like:
>>
>> public void run() {
>>         try {
>>               while(running)
>>                    // processing logic
>>               }
>>         } catch (InterruptedException e) {
>>             LOG.error("Unexpected interruption", e);
>>         } catch (RequestProcessorException e) {
>>             LOG.error("Unexpected exception", e);
>>         } catch (Exception e) {
>>             LOG.error("Unexpected exception", e);
>>         }
>>         LOG.info("...exited loop!");
>> }
>>
>> I feel, we could improve our threads  in our system. From the design I could see,
there could be a chance of silently leaving the thread in case of any exception(abnormal or
any functional issue too) If this happens in the production, the server would get hanged forever
and will not be able to deliver its role.
>>
>> If we have a 'DeathWatcher 'or some other mechanism in place to monitor all the critical
threads. It can take a decision like - bring down the process if required, or shutdown the
quorumpeer and go for LE again etc.
>> Now the monitoring or management tool will knows about the situation and can act
upon.
>>
>> Appreciate any thoughts ?
>>
>> Thanks in advance,
>> Rakesh R

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