[Spread-users] Big messages in Spread

[Ben Laurie]

Jonathan Stanton wrote:
> 
> On Fri, Jul 20, 2001 at 11:16:33AM -0600, Roel van der Goot wrote:
> >
> > Since we were encountering some issues with big messages, I found
> > the following two things in Spread that should probably be changed.
> > For completeness sake we are using fibrechannel datagrams that have a
> > maximum of 964 bytes (MAX_PACKET_SIZE == 964):
> >
> >   - MAX_SCATTER_ELEMENTS is defined to be 100 in two files ("sp.h" and
> >     "scatter.h").
> 
> If your concern is that the same constant is defined twice, that is a
> 'bug' although 'harmless' since they are the same number. Actually I think
> the two uses of MAX_SCATTER_ELEMENTS are actually different and they do
> not have to be the same number (but then they need to have different
> names) The client interface could allow a different maximum number of
> scatter elements in SP_scat_multicast and SP_scat_receive calls then the
> daemon uses internally. The actual requirement is that the client does not
> send a message larger to total size then then daemon can handle.
> 
>  >
> actually sp.c (from your second email)
> >   - scatter.c uses 1440 as a constant instead of (MAX_PACKET_SIZE - 32)
> >     where I don't know what the 32 represents. May be the 32 should
> >     become a defined constant depending on its meaning.
> 
> This is an oversight. 1440 should not be hardcoded in. The 32 bytes is
> used to store the packet header. In the daemon code we do have a way to
> get that number without hardcoding it. I'll see how the client should know
> this.
> 
> Here is the real question, which I would be interested in anyone's
> opinions on.
> 
> What should the maximum message size supported by a Spread
> client library be?

Ideally, as big as you can fit in memory (real or virtual). The
application can decide how stupid it is to do that.

> Should that size depend on the way the daemon is compiled (i.e.
> MAX_PACKET_SIZE)?

Only insofar as it isn't possible to avoid.

Cheers,

Ben.

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