[infinispan-dev] design for cluster events (wiki page)

[Mircea Markus]

On Nov 1, 2013, at 7:10 AM, Bela Ban <bban at redhat.com> wrote:

> On 10/31/13 4:45 PM, Dennis Reed wrote:
>> On 10/31/2013 02:18 AM, Bela Ban wrote:
>>> 
>>>> Also if we did have read only, what criteria would cause those nodes
>>>> to be writeable again?
>>> Once you become the primary partition, e.g. when a view is received
>>> where view.size() >= N where N is a predefined threshold. Can be
>>> different, as long as it is deterministic.
>>> 
>>>> There is no guarantee when the other nodes
>>>> will ever come back up or if there will ever be additional ones anytime soon.
>>> If a system picks the Primary Partition approach, then it can become
>>> completely inaccessible (read-only). In this case, I envisage that a
>>> sysadmin will be notified, who can then start additional nodes for the
>>> system to acquire primary partition and become accessible again.
>> 
>> There should be a way to manually modify the primary partition status.
>> So if the admin knows the nodes will never return, they can manually
>> enable the partition.
>> 
>> Also, the PartitionContext should know whether the nodes left normally
>> or not.
>> If you have 5 nodes in a cluster, and you shut down 3 of them, you'll
>> want the remaining two to remain available.
>> But if there was a network partition, you wouldn't.  So it needs to know
>> the difference.
> 
> JGroups won't tell you, and I don't want to add a flag to each member of 
> a view telling you whether it was a graceful or crash-leave.
> 
> However, you (Infinispan) could send a LEAVE message shortly before 
> leaving, which is stored by everyone (or only the coord?). When the view 
> is received, we should be able to determine who left and who crashed.

yes, the ST process makes that differentiation.

Cheers,
-- 
Mircea Markus
Infinispan lead (www.infinispan.org)