[infinispan-dev] Distribution, take 2

[Galder Zamarreno]

On 07/20/2009 12:36 PM, Manik Surtani wrote:
>
> On 20 Jul 2009, at 09:24, Galder Zamarreno wrote:
>
>>
>>
>> On 07/17/2009 08:24 PM, Manik Surtani wrote:
>>> 6.3. Nodes (L - replCount + 1), (L + 1) and (L + replCount) kick off a
>>> LeaveTask.
>>
>> Shouldn't (L - replCount + 1) be (L - 1) ?
>
> Well spotted. That was leftover from an earlier version I was working
> on. It should be (L - 1).
>
>>
>>> 6.3.1. Not everyone in the cluster need be involved in this rehash
>>> thanks to fixed CH positions.
>>>
>>> 7. LeaveTask: This is PUSH based
>>> 7.1. If an existing LeaveTask is running, the existing task should be
>>> cancelled first.
>>
>> Why should it be cancelled? In a cluster of 3 nodes, A:B:C:D, imagine
>> A leaves and while B is pushing state for A, C leaves as well. Are you
>> gonna cancel B's push?
>
> So in the case of cluster {A, B, C, D, E, F}
>
> Let's take the case of C leaving.
>
> B pushes C's state to D.
>
> This task being cancelled will only happen if A or D were to leave
> (others leaving will not trigger a LeaveTask on B)
>
> So if D leaves, it should be cancelled and restarted since there is no
> point in beaming state to D. Even if A leaves, a rehash should only
> happen once. So a rehash due to A leaving should cover state being
> pushed to D as well.

Hmmmm, good point. It's A leaving while B's pushing C's state to D that 
I didn't have it clear.

What about this? C is leaving, B pushes C's state to D, so D is running 
LeaveTask as receiver. Now, E leaves. D needs to start a Leave task as 
pusher, shouldn't it? If the data was disjoint, the two Leave tasks 
could operate in parallel. I suppose this is the concurrent leave case 
you're mentioning earlier.

>
> While typing this I realised that points 7.4.1 and 8.2. in my original
> email will prevent this from working since the conditions in those steps
> do not assume that a task could be cancelled. A potential way for this
> is to maintain a "leavers list". Every time a LeaveTask completes, the
> LeaversList is emptied. Every time the LeaveTask starts, it adds the
> leaver's address to the LeaversList. Conditions 7.4.1 and 8.2 consider
> all leavers in the LeaversList, not just the current leaver, L.
>
> Thoughts?

Hmmm, but could u update the LeaversList while 7.4.1 or 8.2 is going on? 
That task is tied to OLD_CH and the moment there's a new leaver, you 
have a new OLD_CH. Or would you iterate over the list of leavers that 
and for each iterate over all keys in data container? That sounds expensive.

>
> Cheers
> Manik
>
> --
> Manik Surtani
> manik at jboss.org
> Lead, Infinispan
> Lead, JBoss Cache
> http://www.infinispan.org
> http://www.jbosscache.org
>
>
>
>

-- 
Galder Zamarreño
Sr. Software Engineer
Infinispan, JBoss Cache