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From "Jeff Jirsa"<jji...@apache.org>
Subject Re: Multiple nodes decommission
Date Wed, 19 Apr 2017 06:17:44 GMT


On 2017-04-12 11:30 (-0700), Vlad <qa23d-vvd@yahoo.com> wrote: 
> Interesting, there is no such explicit warning for v.3 https://docs.datastax.com/en/cassandra/3.0/cassandra/operations/opsAddNodeToCluster.html
> It says   
>    - Start the bootstrap node.
>    - verify that the node is fully bootstrapped and all other nodes are up (UN)
> 
> Does it mean that we should start them one by one? May somebody from developers can clarify
this issue? 

You should treat range movements (bootstrap/decom/etc) in 3.0 the same way you treated 2.0/2.1/2.2
- there's nothing special (as far as I know) to make it any more safe than 2.x was.

The warnings and restrictions are because simultaneous range movements PROBABLY violate your
assumed consistency guarantees if you're using vnodes. If you're using single token, this
can be avoided. 

If you really know what you're doing, you can tell cassandra to let you do simultaneous range
movements anyway. There's a system property (actually 2) that will let you tell cassandra
you know the tradeoffs, and then you can bootstrap/decom/etc more than one node at a time.
Generally, it's one of those things where if you have to ask about it, you probably should
just stick to the default one-at-a-time guidelines (which isn't meant to sound condescending,
but it's an area where you can definitely violate consistency and maybe even lose data if
you're not sure).

- Jeff

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