Isend max.message size?

Hello,

I'm here for first time and I'm interested about myrinet technology.
Now, I'm also student of Czech Technical University in Praque, chair of C=
omputer
Science.
I am implementing Segmented version of paralel quicksort alghoritm which =
I
tested on university's myrinet cluster called star(star.felk.cvut.cz).

The problem is:
When I used MPI_Isend function for exchanging data between processors (se=
nding
for ex. one huge message containing thousands of MPI_DOUBLE members!) and=
 test
the end of the Isend by MPI_Test function...the repeat loop will never en=
d
(means that data won't be send).

When the count (number of members are less) then everything is O.K. and M=
PI_Test
 will finish both loops.

I try to write simple code for better undertanding:

.....
MPI_Isend(databuf,count,MPI_DOUBLE,dest,tag,MPI_COMM_WORLD,&request1);
MPI_Isend(indexbuf,count, MPI_UNSIGNED,dest,tag,MPI_COMM_WORLD,&request2)=
;
do {
      MPI_Test(&request1, &flg, &status);
    } while (!flg);
do {
      MPI_Test(&request2, &flg, &status);
    } while (!flg);

/* dealocation of buffers */

Is it a problem with count parameter (number of items) resp.  message is =
too
huge? What is the maximal message size that I can send?

Thanks a lot. Jiri Tomanek