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From Alain RODRIGUEZ <arodr...@gmail.com>
Subject Re: Default Single DataCenter -> Multi DataCenter
Date Mon, 10 Sep 2018 12:14:26 GMT
Adding a data center for the first time is a bit tricky when you
haven't been considering it from the start.

I operate 5 nodes cluster (3.11.0) in a single data center with
> SimpleSnitch, SimpleStrategy and all client policy RoundRobin.
>

You will need:

- To change clients, make them 'DCAware'. This depends on the client, but
you should be able to find this in your Cassandra driver (client side).
- To change clients, make them use 'LOCAL_<WHATEVER>' consistency
('LOCAL_ONE'/'LOCAL_QUORUM' being the most common).
- To change 'SimpleSnitch' for 'EC2Snitch' or 'GossipingPropertyFileSnitch'
for example, depending on your context/preference
- To change 'SimpleStrategy' for 'NetworkTopologyStrategy' for all the
keyspaces, with the desired RF. I take the chance to say that switching to
1 replica only is often a mistake, you can indeed have data loss (which you
accept) but also service going down, anytime you restart a node or that a
node goes down. If you are ok with RF=1, RDBMS might be a better choice.
It's an anti-pattern of some kind to run Cassandra with RF=1. Yet up to
you, this is not our topic :). In the same kind of off-topic
recommendations, I would not stick with C*3.11.0, but go to C*3.11.3 (if
you do not perform slice delete, there is still a bug with this apparently)

So this all needs to be done *before* starting adding the new data center.
Changing the snitch is tricky, make sure that the new snitch uses the racks
and dc names currently in use in your cluster for the current cluster, if
not the data could not be accessible after the configuration change.

Then the procedure to add a data center is probably described around. I
know I did this detailed description in 2014, here it is:
https://mail-archives.apache.org/mod_mbox/cassandra-user/201406.mbox/%3CCA+VSrLopop7Th8nX20aOZ3As75g2jrJm3ryX119dekLYNHqFwA@mail.gmail.com%3E,
but you might find better/more recent documentation than this one for this
relatively common process, like the documentation you linked.

If you are not confident or have doubts, you can share more about the
context and post your exact plan, as I did years ago in the mail previously
linked. People here should be able to confirm the process is ok before you
move forward, giving you an extra confidence.

C*heers,
-----------------------
Alain Rodriguez - @arodream - alain@thelastpickle.com
France / Spain

The Last Pickle - Apache Cassandra Consulting
http://www.thelastpickle.com

Le lun. 10 sept. 2018 à 11:05, Eunsu Kim <eunsu.bill23@gmail.com> a écrit :

> Hello everyone
>
> I operate 5 nodes cluster (3.11.0) in a single data center with
> SimpleSnitch, SimpleStrategy and all client policy RoundRobin.
>
> At this point, I am going to create clusters of the same size in different
> data centers.
>
> I think these two documents are appropriate, but there is confusion
> because they are referenced to each other.
>
>
> https://docs.datastax.com/en/cassandra/3.0/cassandra/operations/opsAddDCToCluster.html
>
> https://docs.datastax.com/en/cassandra/3.0/cassandra/operations/opsSwitchSnitch.html
>
> Anyone who can clearly guide the order? Currently RF is 2 and I want to
> have only one replica in the NetworkTopologyStrategy.
> A little data loss is okay.
>
> Thank you in advanced..
>
>
>
>
>
>
>

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