[infinispan-dev] Use cases for x-datacenter replication

[Erik Salter]

Hi all,

Since I'm deploying my applications into 3 data centers, I commented at the
wiki site.  Since the bulk of the discussion seems to be here, I'll offer
some additional thoughts.


- First and foremost, I have three data centers (JGRP-1313).  All of my data
centers follow a model where the data is partitioned between them with
geographic failover.
- These data centers have about 50-70 ms latency (RTT) between them.  That
means I (and the customer) can live with synchronous replication for the
time being, especially for the transactional scenario.  In fact, in one of
my cache use cases, this is almost required. 
- In the current state transfer model, a node joining means that all the
nodes from all the sites are involved in rehashing.  The rehash operation
should be enhanced in this case to prefer using the local nodes as state
providers.  I know that this cannot be necessarily guaranteed, as a loss of
multiple nodes at a site might mean the state only exists on another data
center.  But for a minimum of 10M records, I can't afford the existing
limitations on state transfer.  (And it goes without saying the NBST is an
absolute must)
- I will need a custom consistent hash that is data center-aware that can
group keys into a local site.  All of my data is site-specific.
- I mentioned a +1 model for local key ownership on the wiki,  Taking that a
step further, has there been any thought to a quorum model?  Here's what I'm
concerned about.  Most of the time, a data center won't fail -- rather
there'll be some intermittent packet loss between the two.  If I have 2
owners on the key's local data center and 1 each on the backup sites, I may
not want to rehash if I can't reach a data center.  I can understand if a
prepared tx fails -- those I can retry in application code.  

I'm sure I'll have more =)

Erik

-----Original Message-----
From: infinispan-dev-bounces at lists.jboss.org
[mailto:infinispan-dev-bounces at lists.jboss.org] On Behalf Of Mircea Markus
Sent: Monday, February 13, 2012 11:38 AM
To: infinispan -Dev List
Subject: [infinispan-dev] Use cases for x-datacenter replication

Hi,

>From the discussions we had, I've identified two use cases for the
x-datatcenter replication and added them here:
https://community.jboss.org/wiki/CrossDatacenterReplication-Design
Can you please review and comment? In particular, I don't have a use case
that requires both datacenters to be active at the same time, i.e.
concurrent writes happen at both sites. 
 
Cheers
Mircea
--
Mircea Markus
twitter.com/mirceamarkus

Sr. Software Engineer, Infinispan
http://www.infinispan.org

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