The SOAIncomingRequests_maxThreads property by default is configured based in the SOADataSource data source in Oracle WebLogic Remote Console. This setting may be not enough for REST services under a heavy load (for example, if you have 200 concurrent users in a scenario in which a REST reference is calling a REST service within the same node). You must increase the SOAIncomingRequests_maxThreads value to 400 to avoid the exception error shown in the following example:

<May 2, 2014 10:16:11 AM PDT> <Error> <oracle.soa.bpel.system> <BEA-000000>
<cube engineJTA transaction is not in active state.
The transaction became inactive when executing activity "" for instance
"30,023", bpel engine can not proceed further without an active transaction.
please debug the invoked subsystem on why the transaction is not in active
status. the transaction status is "MARKED_ROLLBACK".
The reason was The execution of this instance "30023" for process
"BuyCoffeeBPELProcess" is supposed to be in an active jta transaction, the
current transaction status is "MARKED_ROLLBACK", the underlying exception is
"Service Unavailable" .
Consult the system administrator regarding this error.
, Cikey=30023, FlowId=20014, Current Activity Key=30023-BpInv0-BpSeq0.3-3,
Current Activity Label=InvokeCreateOrder,
ComponentDN=default/CoffeeShopClient!1.0*soa_19d4a881-115b-42c5-824d-1af3fa766
62d/BuyCoffeeBPELProcess
oracle.fabric.common.FabricInvocationException: Service Unavailable
        at
. . .
. . .