> Regarding the composite traits, one embarrassing thing I can see so far > is about the method RelTraitSet#simplify[3]. >the traits just simply get wiped.
Exactly. Of course no one knows how it should work, however making "RelTraitSet#simplify" a no-op does heal certain cases, and it looks like it does not make things worse. I proposed that solution in https://issues.apache.org/jira/browse/CALCITE-2593?focusedCommentId=16750377&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-16750377 Julian offered his help to find the solution on 23Jan (see 2593). Apparently Julian is not active with regard to 2593 / composites, so I'm inlined to commit the fix. Vladimir
