How does solr store multiple references to same child document from different parent documents?

Question

According to link , the parent child docs are stored as

child1,child2,parent

Does this mean if I have references to child1 from parent1 and parent2, it will be duplicated twice or will it refer to the same child1 document?

Will it be 
child1(COPY1),child2,parent1    ///  child1(COPY2),parent2

OR 
child1(COPY1),parent1 ///// child1(COPY1),parent2

Answer 1

After experimenting a bit with nested documents I came to a conclusion that, when it comes to updating index solr treats parent and all its children as one atomic document. This document is identified by parent's id. There is no such thing as a reference to a child. Child is a part of one atomic document.

This means that when you index two nested documents:

curl http://localhost:8983/solr/demo/update?commitWithin=3000 -d '                                                                                                                                            
[{
  id : parent1,                                                                                                                                                             
  _childDocuments_ : [                                                                                                                                                                                        
    { id: child1},                                                                                                                                                                                                         
    { id: child2}                                                                                                                                                                                                         
  ]                                                                                                                                                                                                           
}, {
  id : parent2,                                                                                                                                                             
  _childDocuments_ : [                                                                                                                                                                                        
    { id: child1}                                                                                                                                                                                                        
  ]                                                                                                                                                                                                           
}]'

you will end up with the following index

child1,child2,parent1,child1,parent2

updating index of parent2-child1 will not affect parent1-child1.