I am using Spring's @async annotation to fire parallel invocation to the DAO methods from a method in Services layer to improve the performance of my RESTful service. However, I do not see any difference in the synchronous and asynchronous approach in terms of response time. In fact the asynchronous approach sometimes takes longer time with multiple errors related to connection time out when concurrent users are looped in during performance testing(com.ibm.websphere.ce.cm.ConnectionWaitTime outException: Connection not available, Timed out waiting for 180009). Even for single request it takes long time, of course, without the connection timeout error. We are using myBatis as the Data Mapper. The following is the Thread Pool configuration in Websphere:
Name Description Min Max

Default 20 20
ORB.thread.pool 10 50
SIBFAPInboundThreadPool Service integration bus FAP inbound channel thread pool 4 50
SIBFAPThreadPool Service integration bus FAP outbound channel thread pool 4 50
SIBJMSRAThreadPool Service Integration Bus JMS Resource Adapter thread pool 35 41
TCPChannel.DCS 5 20
WMQCommonServices WebSphere MQ common services thread pool 1 40
WMQJCAResourceAdapter wmqJcaRaThreadPoolDescription 5 25
WebContainer 50 50
server.startup This pool is used by WebSphere during server startup. 1 3

The wait time for Future task has been set at 300. The maximum time out for Transaction is also set at 300 in Web container in Websphere. was configured in the xml file.

Please advice on the design decision and suggest improvements.