[infinispan-dev] Suppressing state transfer via JMX

Dennis Reed dereed at redhat.com
Fri May 31 12:52:24 EDT 2013 

I see 2 potential issues:

1.  How does the user know which node is the master to connect to, since 
the operations are a no-op on all the others?

     - instead of a no-op, what if the other nodes just forward the 
operation to the correct node?
       Then the user doesn't have to know who the current master is, and 
can just connect to any node.

2.  What if the current master is one of the nodes being stopped?

-Dennis

On 05/31/2013 11:40 AM, Adrian Nistor wrote:
> Yes, ISPN-1394 has a broader scope but the proposed solution for 
> ISPN-3140 solves quite a lot of ISPN-1394 and it's not complex. We 
> might not even need ISPN-1394 soon unless somebody really wants to 
> control data ownership down to segment granularity. If we only want to 
> batch joins/leaves and manually kick out nodes with or without loosing 
> their data then this proposal should be enough. This solution should 
> not prevent implementation of ISPN-1394 in future and will not need to 
> be removed/undone.
>
> Here are the details:
>
> 1. /Add a JMX writable attribute (or operation?) to 
> ClusterTopologyManager (name it suppressRehashing?) that is false by 
> default but should also be configurable via API or xml. While this 
> attribute is true the ClusterTopologyManager queues all 
> join/leave/exclude(see below) requests and does not execute them on 
> the spot as it would normally happen. The value of this attribute is 
> ignored on all nodes but the coordinator. When it is set back to false 
> all queued operations (except the ones that cancel eachother out) are 
> executed. The setter should be synchronous so when setting is back to 
> false it does not return until the queue is empty and all rehashing 
> was processed. /
>
> 2. /We add a JMX operation excludeNodes(list of addresses) to 
> ClusterTopologyManager. Calling this method on any node but the 
> coordinator is no-op. This operation removes the node from the 
> topology (almost as if it left) and forces a rebalance./ The node is 
> still present in the current CH but not in the pending CH. It's 
> basically disowned by all its data which is now being transferred to 
> other (not excluded) nodes. At the end of the rebalance the node is 
> removed from topology for good and can be shut down without loosing 
> data. Note that if suppressRehashing==false operation excludeNodes(..) 
> just queues them for later removal. We can batch multiple such 
> exclusions and then re-activate the rehashing.
>
> The parts that need to be implemented are written in italic above. 
> Everything else is already there.
>
> excludeNodes is a way of achieving a soft shutdown and should be used 
> only if we care about preserving data int the extreme case where the 
> nodes are the last/single owners. We can just kill the node directly 
> if we do not care about its data.
>
> suppressRehashing is a way of achieving some kind of batching of 
> topology changes. This should speed up state transfer a lot because it 
> avoids a lot of pointless reshuffling of data segments when we have 
> many successive joiners/leavers.
>
> So what happens if the current coordinator dies for whatever reason? 
> The new one will take control and will not have knowledge of the 
> existing rehash queue or the previous status of suppressRehashing 
> attribute so it will just get the current cache membership status from 
> all members of current view and proceed with the rehashing as usual. 
> If the user does not want this he can set a default value of true for 
> suppressRehashing. The admin has to interact now via JMX with the new 
> coordinator. But that's not as bad as the alternative where all the 
> nodes are involved in this jmx scheme :) I think having only the 
> coordinator involved in this is a plus.
>
> Manik, how does this fit for the full and partial shutdown?
>
> Cheers
> Adi
>
>
> On 05/31/2013 04:20 PM, Manik Surtani wrote:
>>
>> On 31 May 2013, at 13:52, Dan Berindei <dan.berindei at gmail.com 
>> <mailto:dan.berindei at gmail.com>> wrote:
>>
>>> If we only want to deal with full cluster shutdown, then I think 
>>> stopping all application requests, calling Cache.clear() on one 
>>> node, and then shutting down all the nodes should be simpler. On 
>>> start, assuming no cache store, the caches will start empty, so 
>>> starting all the nodes at once and only allowing application 
>>> requests when they've all joined should also work without extra work.
>>>
>>> If we only want to stop a part of the cluster, suppressing 
>>> rebalancing would be better, because we wouldn't lose all the data. 
>>> But we'd still lose the keys whose owners are all among the nodes we 
>>> want to stop. I've discussed this with Adrian, and we think if we 
>>> want to stop a part of the cluster without losing data we need a JMX 
>>> operation on the coordinator that will "atomically" remove a set of 
>>> nodes from the CH. After the operation completes, the user will know 
>>> it's safe to stop those nodes without losing data.
>>
>> I think the no-data-loss option is bigger scope, perhaps part of 
>> ISPN-1394.  And that's not what I am asking about.
>>
>>> When it comes to starting a part of the cluster, a "pause 
>>> rebalancing" option would probably be better - but again, on the 
>>> coordinator, not on each joining node. And clearly, if more than 
>>> numOwner nodes leave while rebalancing is suspended, data will be lost.
>>
>> Yup.  This sort of option would only be used where data loss isn't an 
>> issue (such as a distributed cache).  Where data loss is an issue, 
>> we'd need more control - ISPN-1394.
>>
>>>
>>> Cheers
>>> Dan
>>>
>>>
>>>
>>> On Fri, May 31, 2013 at 12:17 PM, Manik Surtani <msurtani at redhat.com 
>>> <mailto:msurtani at redhat.com>> wrote:
>>>
>>>     Guys
>>>
>>>     We've discussed ISPN-3140 elsewhere before, I'm brining it to
>>>     this forum now.
>>>
>>>     https://issues.jboss.org/browse/ISPN-3140
>>>
>>>     Any thoughts/concerns?  Particularly looking to hear from Dan or
>>>     Adrian about viability, complexity, ease of implementation.
>>>
>>>     Thanks
>>>     Manik
>>>     --
>>>     Manik Surtani
>>>     manik at jboss.org <mailto:manik at jboss.org>
>>>     twitter.com/maniksurtani <http://twitter.com/maniksurtani>
>>>
>>>     Platform Architect, JBoss Data Grid
>>>     http://red.ht/data-grid
>>>
>>>
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>>
>> --
>> Manik Surtani
>> manik at jboss.org <mailto:manik at jboss.org>
>> twitter.com/maniksurtani <http://twitter.com/maniksurtani>
>>
>> Platform Architect, JBoss Data Grid
>> http://red.ht/data-grid
>>
>>
>>
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