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From "Christopher Wirt" <chris.w...@struq.com>
Subject RE: How to determine which node(s) an insert would go to in C* 2.0 with vnodes?
Date Tue, 08 Oct 2013 11:07:25 GMT
In CQL there is a token() function you can use to find the result of your
partitioning schemes hash function for any value.

 

e.g. select token(value) from column_family1 where partition_column = value;

 

You then need to find out which nodes are responsible for that value using
nodetool ring or looking at system.peers table for tokens

 

Not that straight forward esp. with 100 nodes and vNodes. Maybe someone has
written a script or something to do this already?

 

Or I suppose you could turn on tracing and repeat the query until you've
seen it hit three different end nodes?

i.e.

tracing on;

select * from column_family1 where partition_column = value;

 

 

 

From: Sameer Farooqui [mailto:sameer@blueplastic.com] 
Sent: 08 October 2013 10:20
To: user@cassandra.apache.org
Subject: How to determine which node(s) an insert would go to in C* 2.0 with
vnodes?

 

Hi,

When using C* 2.0 in a large 100 node cluster with Murmer3Hash, vnodes and
256 tokens assigned to each node, is it possible to find out where a certain
key is destined to go?

If the keyspace defined has replication factor = 3, then a specific key like
'row-1' would be destined to go to 3 nodes, right? Is there a way I can
pre-determine which of the 3 nodes out of 100 that that insert of 'row-1'
would go to?

Or alternatively, after I've already written the 'row-1', can I find out
which 3 nodes it went to?


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