Tomorrow, I will again begin the process of updating CiviCRM. I know that as the upgrade process is going through 4.7.8, it upgrades mailing foreign key constraints in `civicrm_mailing_event_queue` and `civicrm_mailing_recipients` tables, which have 2,230,662 and 3,025,260 rows, respectively. This causes this portion of the upgrade to be extremely long, and I had thought it stalled. 

 1. What exactly are these tables for?
 2. How can I trim these tables down a bit?
 3. What are the ramifications of trimming it?

`Describe civicrm_mailing_event_queue` in mysql:

    +------------+------------------+------+-----+---------+----------------+
    | Field      | Type             | Null | Key | Default | Extra          |
    +------------+------------------+------+-----+---------+----------------+
    | id         | int(10) unsigned | NO   | PRI | NULL    | auto_increment |
    | job_id     | int(10) unsigned | NO   | MUL | NULL    |                |
    | email_id   | int(10) unsigned | YES  | MUL | NULL    |                |
    | contact_id | int(10) unsigned | NO   | MUL | NULL    |                |
    | hash       | varchar(255)     | NO   |     | NULL    |                |
    | phone_id   | int(10) unsigned | YES  | MUL | NULL    |                |
    +------------+------------------+------+-----+---------+----------------+

`Describe civicrm_mailing_recipients` in mysql:

    +------------+------------------+------+-----+---------+----------------+
    | Field      | Type             | Null | Key | Default | Extra          |
    +------------+------------------+------+-----+---------+----------------+
    | id         | int(10) unsigned | NO   | PRI | NULL    | auto_increment |
    | mailing_id | int(10) unsigned | NO   | MUL | NULL    |                |
    | contact_id | int(10) unsigned | NO   | MUL | NULL    |                |
    | email_id   | int(10) unsigned | YES  | MUL | NULL    |                |
    | phone_id   | int(10) unsigned | YES  | MUL | NULL    |                |
    +------------+------------------+------+-----+---------+----------------+
   
Thanks in advance!