I got a large table with million of records. I have to do a `count(*)` for a certain criteria and there is no way I can get rid of it.

`count()` with `InnoDB` is very expensive. I have been trying to figure out different configurations for MySQL but all in vain. Can't speed up the count. The application requires the result to be less than 1 second because there are other dependent queries to run. 

Any indexes are not helping because of the way InnoDB counts.

```
mysql> EXPLAIN SELECT count(*) FROM `callrequests` WHERE active_call = 1;
+----+-------------+--------------+-------+---------------+-------------+---------+------+---------+--------------------------+
| id | select_type | table        | type  | possible_keys | key         | key_len | ref  | rows    | Extra                    |
+----+-------------+--------------+-------+---------------+-------------+---------+------+---------+--------------------------+
|  1 | SIMPLE      | callrequests | index | NULL          | active_call | 6       | NULL | 5271135 | Using where; Using index |
+----+-------------+--------------+-------+---------------+-------------+---------+------+---------+--------------------------+

mysql> show index from callrequests;
+--------------+------------+------------------------------+--------------+--------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| Table        | Non_unique | Key_name                     | Seq_in_index | Column_name  | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |
+--------------+------------+------------------------------+--------------+--------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| callrequests |          0 | PRIMARY                      |            1 | id           | A         |     5271135 |     NULL | NULL   |      | BTREE      |         |               |
| callrequests |          0 | PRIMARY                      |            2 | campaign_id  | A         |     5271135 |     NULL | NULL   |      | BTREE      |         |               |
| callrequests |          0 | unique_contact               |            1 | campaign_id  | A         |        4849 |     NULL | NULL   |      | BTREE      |         |               |
| callrequests |          0 | unique_contact               |            2 | contact_id   | A         |     5271135 |     NULL | NULL   |      | BTREE      |         |               |
| callrequests |          0 | unique_contact               |            3 | contact      | A         |     5271135 |     NULL | NULL   |      | BTREE      |         |               |
| callrequests |          1 | fk_callrequest_campaign1_idx |            1 | campaign_id  | A         |          10 |     NULL | NULL   |      | BTREE      |         |               |
| callrequests |          1 | index4                       |            1 | campaign_id  | A         |        2506 |     NULL | NULL   |      | BTREE      |         |               |
| callrequests |          1 | index4                       |            2 | contact      | A         |     5271135 |     NULL | NULL   |      | BTREE      |         |               |
| callrequests |          1 | phonbook_id_index            |            1 | phonebook_id | A         |          10 |     NULL | NULL   |      | BTREE      |         |               |
| callrequests |          1 | dnc_group_id_index           |            1 | dnc_group_id | A         |           2 |     NULL | NULL   |      | BTREE      |         |               |
| callrequests |          1 | active_call                  |            1 | campaign_id  | A         |          12 |     NULL | NULL   |      | BTREE      |         |               |
| callrequests |          1 | active_call                  |            2 | active_call  | A         |          16 |     NULL | NULL   | YES  | BTREE      |         |               |
| callrequests |          1 | call_status                  |            1 | call_status  | A         |        2518 |     NULL | NULL   |      | BTREE      |         |               |
| callrequests |          1 | call_status                  |            2 | processed    | A         |        2518 |     NULL | NULL   |      | BTREE      |         |               |
| callrequests |          1 | call_status                  |            3 | active_call  | A         |        2518 |     NULL | NULL   | YES  | BTREE      |         |               |
+--------------+------------+------------------------------+--------------+--------------+-----------+-------------+----------+--------+------+------------+---------+---------------+

```

The server is 
`Xeon machine with 12 CPU cores and 64 GB RAM dedicated 5.6.14-62.0 Percona Server`

My `innodb_buffer_pool_size` is `38 GB` and all of data sits in innodb buffer pool.