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<p class="MsoNormal">My application uses mainly inter-communicators rather than intra-communicators for fault tolerance. A particular process might have 20 inter-communicators active at one time. I’m receiving the warning<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">[mpiexec@n010.cluster.com] WARNING: too many ssh connections to n009.cluster.com; waiting 6 seconds<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">What is the cause of this? I have several guesses:<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoListParagraph" style="text-indent:-.25in;mso-list:l0 level1 lfo2"><![if !supportLists]><span style="mso-list:Ignore">1)<span style="font:7.0pt "Times New Roman"">
</span></span><![endif]>MPICH has an internal limit on the number of connections<o:p></o:p></p>
<p class="MsoListParagraph" style="text-indent:-.25in;mso-list:l0 level1 lfo2"><![if !supportLists]><span style="mso-list:Ignore">2)<span style="font:7.0pt "Times New Roman"">
</span></span><![endif]>I’m bumping up against a Linux limit on the number of connections<o:p></o:p></p>
<p class="MsoListParagraph" style="text-indent:-.25in;mso-list:l0 level1 lfo2"><![if !supportLists]><span style="mso-list:Ignore">3)<span style="font:7.0pt "Times New Roman"">
</span></span><![endif]>Non-blocking communication using MPI_Isend() creates a temporary ssh connection (not likely)<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">The other question is, what are the consequences of “waiting 6 seconds”? Are some non-blocking messages dropped?<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I’m using MPICH 3.3.2, CentOS 3.10 and the Portland Group compiler pgc++ 19.5.0.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
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