EM.run {
   db = EM.connect_unix_domain( "/tmp/.s.PGSQL.5432", EM::P::Postgres3 )
   db.connect( "mydb", "myuser", "" ).callback do |status|
     if status
       db.query( "select * from largish_table_with_200k_rows" ).callback do |status, result, errors|
         if status
           result.rows.each do |row|
             p row
           end
         end
       end
     end
   end
}