[MPICH] Maximum message length

[Rob Ross]

Hi James,

The implementation shouldn't have trouble figuring out what to do with 
very large messages.  Just do whatever is most convenient for you.

Defining a contig type with a large count might be a simple solution.

Regards,

Rob

James S Perrin wrote:
> Ashley Pittman wrote:
> 
>> On Thu, 2006-01-05 at 12:14 +0000, James S Perrin wrote:
>>
>>> Hi,
>>>     As the in Sends/Recvs message count is defined as an int (32bit) 
>>> is the maximum message count 2^31 or (2^31)/sizeof(datatype) ie the 
>>> number of bytes is limited to 2^31 ? Is this behaviour implementation 
>>> specific?
>>
>>
>> This isn't quite right, the maximum count is 2^31 as you say but the
>> maximum message size if (2^31)*sizeof(datatype). 
> 
> Thanks that answers my question.
> 
>> Given that a int is 4
>> bytes allows 8Gb transfers, if you want more just use a larger
>> datatypes.
> 
> No, I need to send messages of any datatype where count > 2^31. Though I 
> could
> define a large array of datatype as a new MPI_Type I would think it 
> better to
> send the messages in chunks of 2^31 (or less)?
> 
> Regards
> James