I was hoping to transition my "simple" cassandra cluster (where each node is a
cassandra + hadoop tasktracker) to a cluster with two virtual datacenters
(vanilla cassandra vs. cassandra + hadoop tasktracker), based on this:
http://wiki.apache.org/cassandra/HadoopSupport#ClusterConfig
The problem I'm having is my hadoop jobs are getting heavy enough it's
affecting my user facing performance on my cluster.
Right now I'm in AWS, and I have 4 nodes in us-east split over two availability
zones ("us-east-1c" that I'll call "c" and "us-east-1d" that I'll call "d"),
setup with this keyspace:
create keyspace civicscience with replication_factor=3 and strategy_options =
[{us-east:3}] and
placement_strategy='org.apache.cassandra.locator.NetworkTopologyStrategy';
And I'm using the Ec2Snitch.
I'm wondering if I write my own snitch that extends Ec2Snitch with overrides as
follows:
getDC = if(AZ == c || d) return return us-east (to keep current nodes the same)
else return us-east-hadoop;
getRack = return super(); (returning a,b,c,d seems ok)
Then, if I boot N new nodes into us-east-1[a,b] they will be "hadoop" nodes
because of the snitch. I'll obviously have to change my home brew cassandra +
hadoop instances to selectively run task trackers or not (a/b = yes, and c/d =
no).
But:
-Is the overall RF=3 still ok?
-What is the recommended split between "normal" and "hadoop" in terms of
strategy_options (assuming RF=3)? 2/1?
-Can I (how do I safely) change the keyspace strategy_options from
[{us-east:3}] to [{us-east:2, us-east-hadoop:1}] This seems like the
riskiest/most complicated step of everything I've proposed...
-After I change the options, what (if anything) would I have to do to migrate
data around?
One final question: should I add new nodes as Brisk instances instead of my
home brew cassandra + hadoop nodes? I've obviously already put in the
pain/effort of learning how to run hadoop + cassandra...
Thanks for any help/advice!
will
