sql - Mysql Group by time interval optimization -

i have large table (several hundred millions of rows) stores test results along datetime , foreign key related entity called 'link', need to group rows time intervals of 10,15,20,30 , 60 minutes filter time , 'link_id' know can done query explained [here][1]:

select time,avg(rtt),min(rtt),max(rtt),count(*)  trace link_id=1 , time>='2015-01-01' , time <= '2015-01-30' group unix_timestamp(time) div 600; 

this solution worked extremely slow (about 10 on average) tried adding datetime column each 'group interval' example row:

id | time                     | rtt        | link_id 1  | 2014-01-01 12:34:55.4034 | 154.3      | 2 

became:

id | time                     | rtt        | link_id | time_60                   |time_30 ... 1  | 2014-01-01 12:34:55.4034 | 154.3      | 2       | 2014-01-01 12:00:00.00    | 2014-01-01 12:30:00.00 ... 

and intervals following query:

select time_10,avg(rtt),min(rtt),max(rtt),count(*)  trace link_id=1 , time>='2015-01-01' , time <= '2015-01-30' group time_10; 

this query @ least 50% faster (about 5 seconds on average) still pretty slow, how can optimize query faster?

explain query outputs this:

+----+-------------+------------+------+------------------------------------------------------------------------+----------------------------------------------------+---------+-------+---------+----------------------------------------------+ | id | select_type | table      | type | possible_keys                                                          | key                                                | key_len | ref   | rows    |                                        | +----+-------------+------------+------+------------------------------------------------------------------------+----------------------------------------------------+---------+-------+---------+----------------------------------------------+ |  1 | simple      | main_trace | ref  | main_trace_link_id_c6febb11f84677f_fk_main_link_id,main_trace_e7549e3e | main_trace_link_id_c6febb11f84677f_fk_main_link_id | 4       | const | 1478359 | using where; using temporary; using filesort | +----+-------------+------------+------+------------------------------------------------------------------------+----------------------------------------------------+---------+-------+---------+----------------------------------------------+ 

and these table indexes:

+------------+------------+----------------------------------------------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+ | table      | non_unique | key_name                                           | seq_in_index | column_name | collation | cardinality | sub_part | packed | null | index_type | comment | index_comment | +------------+------------+----------------------------------------------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+ | main_trace |          0 | primary                                            |            1 | id          |         |     2956718 |     null | null   |      | btree      |         |               | | main_trace |          1 | main_trace_link_id_c6febb11f84677f_fk_main_link_id |            1 | link_id     |         |           2 |     null | null   |      | btree      |         |               | | main_trace |          1 | main_trace_07cc694b                                |            1 | time        |         |     2956718 |     null | null   |      | btree      |         |               | | main_trace |          1 | main_trace_e7549e3e                                |            1 | time_10     |         |       22230 |     null | null   | yes  | btree      |         |               | | main_trace |          1 | main_trace_01af8333                                |            1 | time_15     |         |       14783 |     null | null   | yes  | btree      |         |               | | main_trace |          1 | main_trace_1681ff94                                |            1 | time_20     |         |       10870 |     null | null   | yes  | btree      |         |               | | main_trace |          1 | main_trace_f7c28c93                                |            1 | time_30     |         |        6399 |     null | null   | yes  | btree      |         |               | | main_trace |          1 | main_trace_0f29fcc5                                |            1 | time_60     |         |        3390 |     null | null   | yes  | btree      |         |               | +------------+------------+----------------------------------------------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+ 

for query:

select time_10, avg(rtt), min(rtt), max(rtt), count(*)  trace link_id = 1 , time >= '2015-01-01' , time <= '2015-01-30' group time_10; 

the best index covering index: trace(link_id, time, time_10, rtt).