How to make the search engine use search api db? I have installed search_api, with search_api_db, create 2 indexes, one for node, one for users. 
The conf:


server: search_db server, 
2 indexes: default_node_index and user_index
service class: database service


The one for users has parameters:


field: email (fulltext)
filter:role (limit to one only). 


The index seems working good, it indexes the right number of users, I checked the uids in the db and it is corresponding to the good users. 
But still when I use the search (search/user/something), the search is on the names instead of emails, and the role filter is not applied. So in short, it is not using the search_api_db. It looks like the whole system is overriden by some other fulltext on everything search. I'm stuck here
So ok I found out what is my problem. 
I miss the other entity necessary to build to use the search api db: the search page using the search page module or views, instead of the system search page. 

There is a tutorial here to have a more accurate and complete picture of the process: http://webwash.net/tutorials/intro-search-api-part-1-how-create-search-pages