How can I optimize the view and avoid timeout error

问题

I had a view map/reduce defined as following,as most of documents have no doc.emails[i].userTypecode elements in couchdb, so it is running the view takes too long causing couch to give up / time out: the error is Error: os_preocess_error, OS process time out, can some one help me how to figure out this issue and how to optimize the map/reduce? thank you

I checked there are similar issue happened , but no idea how that were fixed?https://issues.apache.org/jira/browse/COUCHDB-1333 couchdb views os_process_error - big documents

map:

  function(doc) {
                for (var i in doc.emails) {
                     if (doc.emails[i].userTypecode == "false" || !doc.users[i].userTypecode) {
                      emit(doc.emails[i].emailAddress.toLowerCase().split('@')[1],doc);   
                 }
             }
            }

reduce:

function(keys, values, rereduce) {
      return values;
}

来源：https://stackoverflow.com/questions/40119889/how-can-i-optimize-the-view-and-avoid-timeout-error