Comment 1 for bug 1181372

it may be too many requests for db access at the same time.

The TimeoutError "QueuePool limit of size 5 overflow 10 reached, connection timed out, timeout 30" means:
pool size: 5
overflow: 10
timeout: 30

The current connections reached 15 (5+10). The new request will wait 30 seconds (timeout) to acquire connection from the pool or raise the TimeoutError.

setting the flag sql_max_overflow to -1 or larger than 10 might solve this problem.