I found that if I send too many messages to a <chain /> with <filter /> as downstream handler. If the filter contains @Header, the delivery of message will be very slow if works with latest version of SPF.
I will send the test case later.
Please note that this affect Spring Integration that work against latest of SPF (v4.3.4), SPF v4.3.3 doesn't suffer this issue. Hence, I am not sure whether this is the problem of SPF or SI