 				if gotLock
 					callback(null, lockValue)
 				else
-					setTimeout attempt, LockManager.LOCK_TEST_INTERVAL
+					setTimeout attempt, testInterval
+					# back off when the lock is taken to avoid overloading
+					testInterval = Math.max(testInterval * 2, LockManager.MAX_TEST_INTERVAL)
 
 	checkLock: (doc_id, callback = (err, isFree)->)->
 		key = keys.blockingKey(doc_id:doc_id)


	getLock: (doc_id, callback = (error, lockValue) ->) ->
		startTime = Date.now()
		do attempt = () ->
			if Date.now() - startTime > LockManager.MAX_LOCK_WAIT_TIME
				e = new Error("Timeout")


module.exports = LockManager =
	LOCK_TEST_INTERVAL: 50 # 50ms between each test of the lock
	MAX_TEST_INTERVAL: 1000 # back off to 1s between each test of the lock
	MAX_LOCK_WAIT_TIME: 10000 # 10s maximum time to spend trying to get the lock
	LOCK_TTL: 30 # seconds. Time until lock auto expires in redis.

