Changing the stack size and memtable space

Increasing the stack size can improve performance under Tomcat.

Some Solr users have reported that increasing the stack size improves performance under Tomcat. To increase the stack size, uncomment and modify the default -Xss128k setting in the cassandra-env.sh file. Also, decreasing the memtable space to make room for Solr caches might improve performance. Modify the memtable space using the memtable_total_space_in_mb property in the cassandra.yaml file.