[mpich-discuss] Max Communicators Limit

wesley@wesbland.com wbland at anl.gov
Tue Sep 9 13:30:15 CDT 2014

There is a maximum number of communicators, but it’s not exactly standardized or consistent between implementations. In MPICH, the context ID can be up to 32 bits but we reserve some of those so in the end you get something like 16 bits. In reality, you still don’t get all 65,536. Depending on how they are allocated, you’ll get some subset of that.

So in the end, there’s not a good answer. Rob’s answer is probably the best. Try it until it breaks. Most people that we’ve heard running against the barrier have a problem after a few thousand.

On Tue, Sep 9, 2014 at 1:19 PM, Vishwanath, Venkatram <venkat at anl.gov>

> Hi,
> There is a maximum # of communicators one can create. How can I query this limit for MPICH? Is there a standard way to query this limit across MPI implementations?    
> Regards,
> Venkat
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