[omniORB] Marshall exception -- message size limit exceeded

[Philippe Selo]

[re-send to the list]

Duncan and Luke,

Thanks for you answers.

The issue that Henrique was describing is not so much the limit to the
message size as the handling on the server side.
In our system, we have a wrapper on the client side that catches the
COMM_FAILURE exception and retries based on client policies (we
experience a lot of comm failures when we run with a large number of
machines).
When the server's answer to a request is larger than the max size of
the buffer, it sends a very generic COMM_FAILURE and our client
retries again, which is useless. It would help a lot if the server was
sending a more specific exception that the client could distinguish
from a comm failure.

Regards,
Philippe.

On 2/5/07, Duncan Grisby <duncan at grisby.org> wrote:
> On Tuesday 30 January, "Luke Deller" wrote:
>
> > > On the client, side a COMM_FAILURE exception will happen. However, the
> > > minor code does not indicate MARSHAL_MessageSizeExceedLimit (it
> > indicates
> > > COMM_FAILURE_WaitingForReply instead). So the client does not know why
> > the
> > > failure occurred either -- that is that the response is larger than
> > what
> > > can be handled.
> >
> > I see the following comment in src/lib/omniORB/orbcore/giopImpl12.cc, in
> > the function giopImpl12::sendSystemException
> >
> >     // This system exception is raised during the marshalling of the
> > reply.
> >     // We cannot marshal the exception. Can only indicate that something
> >     // fatal about this request.
> >
> > I suppose it makes sense that the server can't change its mind half way
> > through sending a response.   It should be possible to calculate the
> > size of a response *before* starting to send it, but that might be
> > expensive.
>
> Yes -- that's what happens. omniORB does not normally pre-calculate
> message sizes, because to do so involves basically doing all the
> marshalling work twice. Because of that, it doesn't know whether the
> message is going to be too big until it has started sending the message.
>
> > Here's a question of my own:
> > Why does omniORB limit the size of outgoing messages anyway?  I can
> > understand limiting the size of incoming messages, but for outgoing
> > messages the application code is in a position to decide for itself
> > whether to send a certain client call or server reply, right?
>
> Two reasons really. First, if clients are configured to limit the
> incoming message size, it makes sense for servers to similarly limit the
> messages to avoid sending more data than the client will accept.
> Secondly, and probably more importantly, it guards against unpleasant
> behaviour in the face of memory corruption problems. Imagine you're
> sending a sequence and memory corruption sets the sequence length to
> 2^32 items. It's probably a bad thing for omniORB to attempt to send all
> that data.
>
> It would probably make sense to have separate sending and receiving
> limits. Anyone want to make a patch for it?
>
> Cheers,
>
> Duncan.
>
> --
>  -- Duncan Grisby         --
>   -- duncan at grisby.org     --
>    -- http://www.grisby.org --
>
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