[jgroups-users] RPC request and response message prioritization

Hello Bella, et al.,

Background first:

We must prioritize our messages using PrioHeader and RATE_LIMITER2.  To prioritize messages, we add a PrioHeader to the message at the application level.  We have combined the PRIO and RATE_LIMITER2 into a new version of RATE_LIMITER2 - we are no longer are using PRIO.  RATE_LIMITER2 now contains a priority queue to manage the message prioritization.  We are using two instances of RATE_LIMITER2 in the protocol stack, one for prioritized messages (from our application) and one for non-prioritized messages (mostly JGroups messages).   Message either have or do not have a PrioHeader and thus depending on this logic, messages are "in scope" for only one of the RATE_LIMITER2 instances.

Problem:

We use RPC's to send requests to get large data sets.  We use NEAREST to determine the nearest network host from which we will make the data request to optimize the network usage.  I was easily able to modify the RpcDispatcher to add a PrioHeader to the RPC request messages so that the request flows properly through the rate limited stack by adding a priority to the RequestOptions that is an argument to the callRemoteMethod method and then from the RequestOptions extract a priority to add to the message.  This functionality by default is disabled and can be enabled with a function call to the RpcDispatcher.

The problem I have is prioritizing the RPC method response which, as you can image, is where the large amounts of data needs to be transferred.  The problem is that the RequestCorrelator, after calling the RpcDispatcher.handle method, creates the response messages with a fixed set of headers and thus it has removed the PrioHeader that I added in the rsp instance in RpcDispatcher.handle.  Here's the code from the RequestCorrelator


protected void sendResponse(Message rsp, long req_id, boolean is_exception) {
    prepareResponse(rsp);
    Header rsp_hdr=new Header(is_exception? Header.EXC_RSP : Header.RSP, req_id, corr_id);
    rsp.putHeader(corr_id, rsp_hdr);
    if(log.isTraceEnabled())
        log.trace("sending rsp for %d to %s", req_id, rsp.getDest());
    transport.down(new Event(Event.MSG, rsp));
}

My changes thus far (outside of changes to RATE_LIMITER2) have been "additional" functionality that would not impact other JGroups users.  However, when I think about what I would need to do to add a PrioHeader to an RFC response, it makes me pause and reach out to you to see if you have a better solution or another suggestion.

BTW:  We had a similar issue with FRAG2 in that it only preserves the headers for the first fragment - which makes perfect sense - however, the removal of the PrioHeader results in all but the first fragment to be directed to the non-prioritized instance of RATE_LIMITER2.  I modified FRAG2 slightly to add a new property "preserve_headers" which is false by default.  If it is set to true, all message fragments will contain all of the original headers.  Very simple, very clean.

Thanks for your time.


Thanks,

Michael Earl
Software Engineering Manager
All Weather Inc.
1165 National Drive
Sacramento, CA 95834
E-mail: mailto:[email protected]
Cell: 916-521-0453

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