How are Solr's stored and indexed fields stored internally (in Lucene)

Question

In Solr, when I set the field as 'indexed' but not 'stored', it is still stored in the index. If I go the other way around and set the field as 'stored' but not 'indexed', it is also stored in the index if I understand correctly.

My question is, how is the document stored internally in Lucene in these cases? How do 'stored' fields look like in Lucene and how do 'indexed' fields look like in Lucene internally.

The answer to this question will perhaps help me understand why atomic updates in Solr only work with stored fields and not indexed fields (as explained here: https://wiki.apache.org/solr/Atomic_Updates#Stored_Values).

Answer 1

In Solr/Lucene, indexed and stored are two different concepts.

indexed means the field value will be saved in inverted index, and you can search on them when you do query. But you can't see them in search results documents.

stored just means it will be saved in stored field value part, not in inverted index, which means it cannot be searched, but can be used to display when you get search results documents.

Actually, the way how Solr do update is, it will take out the whole document(only stored fields), change the value you want to update, and save them back(with re-index). That's why it can only support stored fields.