Julian, Please go ahead and try the VM.
It looks like recent trait changes defeated MongoAdapter (see my comment in https://issues.apache.org/jira/browse/CALCITE-507) The assert line is "assert traits.allSimple();" Should we try to use helpful messages for the assertions? Having exact contents of "traits" in the assert message would help to analyze issues from Drill/Hive/etc. More interesting question: should we treat this issue as a "backward incompatible change"? If no objections appear, I would add notes from https://issues.apache.org/jira/browse/CALCITE-507?focusedCommentId=14311882&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-14311882 to the HOWTO.md. That would close CALCITE-507. Vladimir
