Index in storage-backend

[harsh]

Hi All

While exploring nutch 2.3.1-gora-mongoDB I exclude the all index 
plugin(basic,index-more,metadata). But found no impact on the 
document.All documents stored in mongoDB having all fields. Is 
IndexWriter is only for Solr/ES. Can we use this for storage-backend. If 
Yes then How? and If No Then what are the ways to add custom-field in 
storage-backend.

Thanks
Harsh