Actually, the fix uses a combination of hostname and random number, which seed is a time stamp. I don’t remember why exactly we didn’t go for the hostname only but I suspect it is because this might not be unique. Adding the random number with a timestamp seed should be robust enough against collisions. Giuseppe

On Jun 6, 2019, at 8:25 AM, Raffenetti, Kenneth J. via discuss <[email protected]> wrote:

On 6/6/19 12:52 AM, Xiaopeng Duan wrote:

...

Thank you, Ken.

We were having another problem with 3.3, and will try it once we fixed our issue.

Just my couriosity, why a random number was chosen for the fix instead of hostname or address? Looks to me the random number still has some possibility to repeat (although very rare), but hostnames and addresses should be unique in a system.

I had the same thought when looking back at this patch. Maybe Giuseppe can share why that was added. I'm fairly sure it can be safely removed.

Ken

...

Regards, Xiaopeng

On Wed, Jun 5, 2019, 8:29 AM Raffenetti, Kenneth J. <[email protected] <mailto:[email protected]>> wrote:

We added a similar fix in https://github.com/pmodels/mpich/pull/2788. This was included in the MPICH 3.3 release.

Ken

On 6/4/19 11:27 PM, Xiaopeng Duan via discuss wrote:

...

Hi, MPICH experts,

We are working on a dynamic master-worker flow using mpi_comm_connect/mpi_com_accept. In some cases when the total number of worker process is large, they may get the same kvs_name and confuse the internal group identifiers. This was traced to the naming convention in HYD_pmcd_pmi_allocate_kvs() that considers only process id, while two processes on different machines may have the same pid. I tried to add host name (from unistd.h>gethostname) to the name, i.e. 'kvs_HOSTNAME_PID_pgid', then everything is working fine in our testing.

So I'm wondering if this change is safe (we may need it for our release) and if it would go into the official MPICH release some time.

Thank you very much.

Xiaopeng

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