[Spread-users] Maximum Message Size

Killeen, Damien Damien.Killeen at dsto.defence.gov.au
Thu Jun 24 05:31:11 EDT 2004

Yes, yet another post about the maximum message size in spread ... our application requires very large messages, up to 16MB.

Going back through the message archives I see one solution is to fragement the messages before sending them, then reconstructing the message at the other end.  This solution is not viable for us as we cannot afford the latency/throughput overheads of the reliable delivery service required to acheive the reliable reconstruction of the message.

I have also seen advice that implies that by changing MAX_SCATTER_ELEMENTS in scatter.h and/or MAX_PACKET_SIZE in data_link.h the resulting MAX_MESSAGE_BODY_LEN in sess_types.h will change accordingly.  I am advised that MAX_PACKET_SIZE is already as large as it can be for the UDP packet size, so my only option is changing MAX_SCATTER_ELEMENTS, from its current value of 100 to around 120000.

I have done this, and successfully started the daemon, and used spflooder and spuser successfully.  However, these programs have hardcoded limits relating to the 100000byte message size that I can't seem to circumvent (changing MAX_BYTES in flooder results in it seg faulting no matter what its input args are).  My own code fails to send the large messages.

In short, my question is, has anyone successfully increased the maximum message size by a substantial amount, and if so what were all the steps? Am I missing something by only changing MAX_SCATTER_ELEMENTS?

Damien Killeen

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