Dear calcite developer community：
I am a user of Apache Calcitite，Recently I discovered that it took
nearly 14 seconds for a simple query to convert sqlnode to relRoot. The reason
was that my query contained about 100 unions. Then I added a relnode cache in
it, and cost time reduced to 300ms. level. Can I open an issue to contribute
this cache back to calcite to deal with poor performance when there are many
unions.thanks
