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From Paul "LeoNerd" Evans <>
Subject Re: Initialising / maintaining a list of nodes in the cluster
Date Sun, 08 Sep 2013 11:03:09 GMT
So I have now found some answers to some of these, but one question
still remains:

On Fri, 6 Sep 2013 23:29:51 +0100
Paul "LeoNerd" Evans <> wrote:

>  * The "system.peers" table identifies peers only by their IP address,
>    not including the port number, whereas TOPOLOGY and STATUS_CHANGE
>    messages include a port.
>    What happens if there is more than one copy of a node using the
>    same IP address?

This can't happen, as the IP address alone is used by Gossip to
identify the nodes.

>    How do I know which TCP port I can use to
>    communicate CQL with a given peer?

It's highly discouraged to use heterogeneous TCP ports for CQL, so in
practice they'll all be the same.

>  * The "system.peers" table doesn't contain any information giving the
>    current availability status of the nodes, so I don't know if they
>    are initially up or down.
>    I can just presume all the known nodes are up until I try
>    connecting to them - in any case, it could be that Cassandra knows
>    of the existence of nodes that for some reason my client can't
>    connect to, so I'd have to handle this case anyway. But it feels
>    like that hint should be there somewhere.

This question still outstanding.

>  * The "system.peers" table doesn't include the actual node I am
>    querying it on.
>    Most of the missing information does appear in the "system.local"
>    table, but not the address. The client does know /an/ address it
>    has connected to that node using, but how can I be sure that this
>    address is the one that will appear in the "peers" list on other
>    nodes? It's quite common for a server to have multiple addresses,
>    so it may be that I've connected to some address different to that
>    which the other nodes know it by.

Turns out it will only accept connections on the IP address it's using
for its peers anyway, so this should be fine.

Paul "LeoNerd" Evans
ICQ# 4135350       |  Registered Linux# 179460

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