Will updating "_mappings" reflect any changes in Indexed data in Elastic search

Question

I didn't found any change in my search result even after updating some fields in my index[_mapping]. so i want to know that "Will updating "_mappings" reflect re-indexing data in Elastic search" [or] "only data inserted after updation will effect with those index parameters[settings n mappings]"

EX:

Initially i've created my index fields as following

           "fname":{  
                 "type":"string",
                 "boost":5
              }
          "lname":{  
                 "type":"string",
                 "boost":1
              }

then i inserted some data. its working fine.

After updating my index mapping as following,

          "fname":{  
                 "type":"string",
                 "boost":1
              }
          "lname":{  
                 "type":"string",
                 "boost":5
              }

Still after updating boost values in index, also i'm getting same result.... why?

     1: after each and every updation of index [settings n mapping], will elastic-search re-index the data again?
     2: do we have different indexed data in same item-type?

Plz clarify this.

Answer 1

While you can add fields to the mappings of an index, any other change to already existing fields will either only operate on new documents or fail.

As mentioned in the comments to the question, there is an interesting article about zero-downtime index switching and there is a whole section about index management in the definitive guide.