Optimizer design of cross_join


1 Is there any optimization for Cross_join such as predicate optimization;I don’t find any optimization in the file of optimizer. And in the file,what does the Optimizer.cpp and L2POptimizer.cpp means to do?I can‘t find any useful messages.

2 Or is there any cost estimation of Cross_join?Or have you ever do some cost estimation about other operations?

3 What does “sg” mean?

4 What does the files of explainLogical/explainPhyscial and echo mean to do?