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<p class="MsoNormal">Matt,<o:p></o:p></p>
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<p class="MsoNormal">Thanks for the quick reply. Users of our ALE3D hydro code at LLNL run very large problems , which I believe can pass in large amounts of local integer data to solver packages like HYPRE and PETSc for global solves. All of our local integer
data is stored with 32-bit indices and switching to 64-bit indices would increase the memory footprint and data motion. This is a problem when running on our BGQ machines like Sequoia machine and potentially for our GPU machines.
<o:p></o:p></p>
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<p class="MsoNormal">Is this not a performance issue for most PETSc users who are running very large problems on 64-bit indices? And is there any interest in the future for allowing local ID’s to be in 32-bit and global ID’s be in 64-bit?
<o:p></o:p></p>
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<p class="MsoNormal">Best,<o:p></o:p></p>
<p class="MsoNormal">Brian<o:p></o:p></p>
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<p class="MsoNormal"><b><span style="font-size:12.0pt;color:black">From: </span></b><span style="font-size:12.0pt;color:black">Matthew Knepley <knepley@gmail.com><br>
<b>Date: </b>Wednesday, January 9, 2019 at 2:56 PM<br>
<b>To: </b>"Weston, Brian Thomas" <weston8@llnl.gov><br>
<b>Cc: </b>PETSc <petsc-users@mcs.anl.gov><br>
<b>Subject: </b>Re: [petsc-users] Data types for local ID's and global ID's for large problems<o:p></o:p></span></p>
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<p class="MsoNormal">On Wed, Jan 9, 2019 at 5:53 PM Weston, Brian Thomas via petsc-users <<a href="mailto:petsc-users@mcs.anl.gov">petsc-users@mcs.anl.gov</a>> wrote:<o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">Does PETSc have different data types for local ID’s and global ID’s? For example, if PETSc is configured for 32-bit indices on very large problems with say 10 billion degrees of
freedoms (exceeding the limit of 32-bit indices for a global ID) would it crash and require us to re-compile with 64-bit indices or can it gracefully handle this?<o:p></o:p></p>
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<p class="MsoNormal">You would need to reconfigure for 64-bit indices. Keeping local indices 32-bit does not do much. I experimented with a local-index-only version several years ago, but it breaks a lot of things, and does not really deliver much benefit.<o:p></o:p></p>
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<p class="MsoNormal"> Thanks,<o:p></o:p></p>
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<p class="MsoNormal"> Matt<o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">Sincerely,<o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">Brian<o:p></o:p></p>
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<p class="MsoNormal">-- <o:p></o:p></p>
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<p class="MsoNormal">What most experimenters take for granted before they begin their experiments is infinitely more interesting than any results to which their experiments lead.<br>
-- Norbert Wiener<o:p></o:p></p>
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<p class="MsoNormal"><a href="http://www.cse.buffalo.edu/~knepley/" target="_blank">https://www.cse.buffalo.edu/~knepley/</a><o:p></o:p></p>
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