On Fri, 2018-02-02 at 17:40 -0800, Wei wrote:

AFAIK, it is due to an attempt of optimisation for distributed
faceting. The relevant JIRA seems to be https://issues.apache.org/jira/
browse/SOLR-8988

Try setting facet.distrib.mco=true

- Toke Eskildsen, Royal Danish Library