DSE Solr nodes and vnodes

Question

The following documentation pages say that it is not recommended to use vnodes for Solr/Hadoop nodes:

http://www.datastax.com/documentation/datastax_enterprise/4.0/datastax_enterprise/srch/srchIntro.html http://www.datastax.com/documentation/datastax_enterprise/4.0/datastax_enterprise/deploy/deployConfigRep.html#configReplication

What is the exact problem with using vnodes for these node types? I inherited a DSE setup wherein the Search nodes all use vnodes, and I wonder if I should take down the cluster and disable vnodes. Is there any harm in leaving vnodes enabled in such a case?

Answer 1

It is primarily a performance concern with DSE/Search since a query needs to fan out internally to enough nodes (or vnodes) to cover the full range of Cassandra rows in the DC, that's a lot more sub-queries when vnodes are enabled.

But, if your performance with vnodes in a DSE/Search DC is acceptable, then you have nothing to worry about.

Answer 2

Isn't the answer applicable only if number of virtual nodes is greater than the actual nodes where we do not configure token ranges manually. So, can actual number of virtual nodes will be more?

If they are same, then whether actual token ranges by manually configuring or by assigning pieces of the ranges using virtual nodes to each node will eventually leave us with same number of nodes, each with a bunch of tokens.

SOLR will have to go as many nodes as number of nodes itself unless virtual nodes themselves are more.