Yeah let me explain why I am doing that.
Actually I was performing reindexing on my data. And I have completed the reindexing from my "old_index" to "new_index" but before shifting entirely to the "new_index", I would like to see if the mapping I defined in the "new_index" working fine for a few days and so I want the data to still be indexed in the "old_index" also. I hopw this makes sense .