I tried running archive.php per your suggestion. It failed several times; each time I doubled the amount of memory to PHP scripts (it's now set to 512MB) and the script timeout limit (it's now set to 300sec). It gives this message...
SQLSTATE[HY000]: General error: 126 Incorrect key file for table '/tmp/#sql_31c3_7.MYI'; try to repair i
SQLSTATE[HY000]: General error: 126 Incorrect key file for table '/tmp/#sql_31c3_7.MYI'; try to repair i