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From Robert Coli <rc...@eventbrite.com>
Subject Re: Can the seeds list be changed at runtime?
Date Tue, 29 Apr 2014 17:13:14 GMT
On Mon, Apr 28, 2014 at 6:57 PM, Lu, Boying <Boying.Lu@emc.com> wrote:

> I wonder if I can change the seeds list at runtime. i.e. without change
> the yaml file and restart DB service?
>

There are dynamic seed providers, Priam for example uses one.

https://issues.apache.org/jira/browse/CASSANDRA-5836

Is a JIRA about the current confusion of the yaml based seed list and what
it means to be a seed, specifically in the context of bootstrapping.

There is a trivial case that illustrates why seed lists need to be dynamic :

1) 3 node cluster, A B C, RF=1.
2) A is a seed, started first. B starts second, C starts third.
3) A and B fail. C does not fail.
4) A and B now have no seed to bootstrap from. C does not consider itself a
seed in its own seed list.
5) C no longer has a node it gossips to once a gossip round, which is one
of the only other seed related difference.

Of course in practice you can just remove A from its own seed list and put
C in A's bootstrap list and bootstrap it. But really what you "should" do
is make C the seed in a dynamic seed provider.

Datastax said :


> The seed node designation has no purpose other than bootstrapping the
> gossip process for new nodes joining the cluster. Seed nodes are not a
> single point of failure, nor do they have any other special purpose in
> cluster operations beyond the bootstrapping of nodes.
>

Seed nodes are also gossiped to once per round, which some might argue
makes them "special".

=Rob

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