Revisit the triggers that update the contribution_source table and look for holes that would make it possible to omit records. Ellery found that 174 of about 6000 donations are not in the contribution_source table,
SELECT *
FROM
civicrm.civicrm_contribution co,
drupal.contribution_tracking ct
LEFT JOIN drupal.contribution_source cs
ON ct.id = cs.contribution_tracking_id
WHERE
co.id = ct.contribution_id
AND ts BETWEEN 20150410120000 AND 20150510000000
AND SUBSTRING_INDEX(ct.utm_source, '.', 1) = 'B15_0410_enUS_dsk_pm_ctl'
-- Select just rows missing a contribution_source
AND cs.contribution_tracking_id is NULLThis is used by @ellery and the Online team to run queries and optimize our campaigns.