Atomic selection of work that prevents race conditions

work_dist_query.sql

UPDATE work
SET
  `worker_id` = ?,
  `worker_claimedAt` = NOW()
WHERE
  (`worker_id` IS NULL
    OR `worker_claimedAt` < DATE_SUB(NOW(), INTERVAL 30 SECOND))
  AND `active` = 1
ORDER BY `worker_lastWork` DESC
LIMIT 1;