Hi there, Fixing an issue in Apache Pinot I've found something that may be a bug in Apache Calcite, although probably is a misunderstanding from my side.
In Pinot we are not (yet) using the standard MetadataHandler (which I'm having issues to understand, but that is not the topic here) to calculate the distribution of each node. Instead, we add our own distribution in a trait and process that by ourselves in our own rules. That may not be the best in terms of DRY, but it is working. We have found an issue when using projections that are not mapping. Probably a more expert eye will see in PinotRelDistributionTraitRule#L113 <http://PinotRelDistributionTraitRule.java#L113> that our naive way to calculate the new distribution fails in that case because project.getMapping() returns null. I planned to solve that by using project.getPartialMapping() in the same way done by Calcite in RelMdDistribution#L165 <https://github.com/apache/calcite/blob/e371b336a8b404ed36955f517196a5e8606455d7/core/src/main/java/org/apache/calcite/rel/metadata/RelMdDistribution.java#L165C17-L165C34>, but when I tried to do that, I found the following runtime exception: java.lang.UnsupportedOperationException at org.apache.calcite.util.mapping.Mappings$AbstractMapping.getSourceOpt(Mappings.java:952) at org.apache.calcite.util.mapping.Mappings$InverseMapping.getTargetOpt(Mappings.java:1841) at org.apache.calcite.rel.RelDistributions$RelDistributionImpl.apply(RelDistributions.java:146) at org.apache.pinot.calcite.rel.rules.PinotRelDistributionTraitRule.deriveDistribution(PinotRelDistributionTraitRule.java:128) Which makes me think there is a problem in the way Project.getPartialMapping is initializing the Mapping. My solution was to do something like: Mappings.TargetMapping mapping = Project.getPartialMapping(input.getRowType().getFieldCount(), project.getProjects()); Mapping actualMapping = Mappings.create(MappingType.PARTIAL_FUNCTION, input.getRowType().getFieldCount(), project.getRowType().getFieldCount()); for (IntPair intPair : mapping) { actualMapping.set(intPair.source, intPair.target); } return inputRelDistribution.apply(actualMapping); But I don't think that is the most elegant solution. I think it is fair to assume that the Mapping returned by Project.getPartialMapping should be usable to call getTargetOpt. Is there something I am doing or understanding wrong?
