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From David Hawthorne <dha...@gmx.3crowd.com>
Subject Re: Replicate On Write behavior
Date Fri, 02 Sep 2011 19:54:28 GMT
Does it always pick the node with the lowest IP address?  All of my hosts are in the same /24.
 The fourth node in the 5 node cluster has the lowest value in the 4th octet (54).  I erased
the cluster and rebuilt it from scratch as a 3 node cluster using the first 3 nodes, and now
the ReplicateOnWrites are all going to the third node, which is also the lowest valued IP
address (55).

That would explain why only 1 node gets writes in a 3 node cluster (RF=3) and why 3 nodes
get writes in a 5 node cluster, and why one of those 3 is taking 66% of the writes.


> 
>> On another note, on a 5-node cluster, I'm only seeing 3 nodes with ReplicateOnWrite
Completed tasks in nodetool tpstats output.  Is that normal?  I'm using RandomPartitioner...
>> 
>> Address         DC          Rack        Status State   Load            Owns    Token
>>                                                                            136112946768375385385349842972707284580
>> 10.0.0.57    datacenter1 rack1       Up     Normal  2.26 GB         20.00%  0
>> 10.0.0.56    datacenter1 rack1       Up     Normal  2.47 GB         20.00%  34028236692093846346337460743176821145
>> 10.0.0.55    datacenter1 rack1       Up     Normal  2.52 GB         20.00%  68056473384187692692674921486353642290
>> 10.0.0.54    datacenter1 rack1       Up     Normal  950.97 MB       20.00%  102084710076281539039012382229530463435
>> 10.0.0.72    datacenter1 rack1       Up     Normal  383.25 MB       20.00%  136112946768375385385349842972707284580
>> 
>> The nodes with ReplicateOnWrites are the 3 in the middle.  The first node and last
node both have a count of 0.  This is a clean cluster, and I've been doing 3k ... 2.5k (decaying
performance) inserts/sec for the last 12 hours.  The last time this test ran, it went all
the way down to 500 inserts/sec before I killed it.
> 
> Could be due to https://issues.apache.org/jira//browse/CASSANDRA-2890.
> 
> --
> Sylvain


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