title: Solr performance: 6.6.0 vs 7.2.1
body: <p>I'm running loadtests on two SolrCloud clusters. Clusters are identical except that one has Solr 6.6.0 with fixed schema, and the other has Solr 7.2.1 with managed schema. Java and garbage collector setting are same on both. Hardware is same too.</p>
  
  <p>Search corpus is identical too: ~400k documents, each size ~5KB size
  I'm loadtesting with two boxes running jmeter v.3.3.
  Solr 6 starts struggling at 200 threads on each jmeter box. Solr 7 almost dies at 100 threads - so apparently Solr6 is a lot more performant with this setup.</p>
  
  <p>Could just Solr version alone cause such a big difference in performance? If not - where should I look to determine what gives this difference?</p>