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<td class="page-title-pattern-first-line " style="padding: 0px; border-collapse: collapse; font-family: Arial, sans-serif; font-size: 14px; padding-top: 10px"> <a href="https://issues.shibboleth.net/jira/browse/MDA" style="color: #3b73af; text-decoration: none">Metadata Aggregator</a> / <a href="https://issues.shibboleth.net/jira/browse/MDA-244" style="color: #3b73af; text-decoration: none"><img src="cid:jira-generated-image-avatar-806df738-b62c-444d-b4cb-ad912adb4ede" height="16" width="16" border="0" align="absmiddle" alt="Improvement" style="vertical-align: text-bottom"></a> <a href="https://issues.shibboleth.net/jira/browse/MDA-244" style="color: #3b73af; text-decoration: none">MDA-244</a> </td>
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<td style="vertical-align: top;; padding: 0px; border-collapse: collapse; padding-right: 5px; font-size: 20px; line-height: 30px; mso-line-height-rule: exactly" class="page-title-pattern-header-container"> <span class="page-title-pattern-header" style="font-family: Arial, sans-serif; padding: 0; font-size: 20px; line-height: 30px; mso-text-raise: 2px; mso-line-height-rule: exactly; vertical-align: middle"> <a href="https://issues.shibboleth.net/jira/browse/MDA-244" style="color: #3b73af; text-decoration: none">Stage to permit explicit parallel execution</a> </span> </td>
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<th style="color: #707070; font: normal 14px/20px Arial, sans-serif; text-align: left; vertical-align: top; padding: 2px 0">Issue Type:</th>
<td class="has-icon" style="padding: 0px; border-collapse: collapse; font: normal 14px/20px Arial, sans-serif; padding: 2px 0 2px 5px; vertical-align: top"> <img src="cid:jira-generated-image-avatar-806df738-b62c-444d-b4cb-ad912adb4ede" height="16" width="16" border="0" align="absmiddle" alt="Improvement" style="vertical-align: text-bottom"> Improvement </td>
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<th style="color: #707070; font: normal 14px/20px Arial, sans-serif; text-align: left; vertical-align: top; padding: 2px 0">Affects Versions:</th>
<td style="padding: 0px; border-collapse: collapse; font: normal 14px/20px Arial, sans-serif; padding: 2px 0 2px 5px; vertical-align: top"> 0.9.2 </td>
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<th style="color: #707070; font: normal 14px/20px Arial, sans-serif; text-align: left; vertical-align: top; padding: 2px 0">Assignee:</th>
<td style="padding: 0px; border-collapse: collapse; font: normal 14px/20px Arial, sans-serif; padding: 2px 0 2px 5px; vertical-align: top"> <a class="user-hover" rel="ian@iay.org.uk" id="email_ian@iay.org.uk" href="https://issues.shibboleth.net/jira/secure/ViewProfile.jspa?name=ian%40iay.org.uk" style="color:#0052cc;; color: #3b73af; text-decoration: none">Ian Young</a> </td>
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<th style="color: #707070; font: normal 14px/20px Arial, sans-serif; text-align: left; vertical-align: top; padding: 2px 0">Components:</th>
<td style="padding: 0px; border-collapse: collapse; font: normal 14px/20px Arial, sans-serif; padding: 2px 0 2px 5px; vertical-align: top"> Pipeline </td>
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<th style="color: #707070; font: normal 14px/20px Arial, sans-serif; text-align: left; vertical-align: top; padding: 2px 0">Created:</th>
<td style="padding: 0px; border-collapse: collapse; font: normal 14px/20px Arial, sans-serif; padding: 2px 0 2px 5px; vertical-align: top"> 03/Jun/20 10:57 AM </td>
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<td class="has-icon" style="padding: 0px; border-collapse: collapse; font: normal 14px/20px Arial, sans-serif; padding: 2px 0 2px 5px; vertical-align: top"> <img src="cid:jira-generated-image-static-major-cba03d79-664b-4de9-ad28-909251eff141" height="16" width="16" border="0" align="absmiddle" alt="Major" style="vertical-align: text-bottom"> Major </td>
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<th style="color: #707070; font: normal 14px/20px Arial, sans-serif; text-align: left; vertical-align: top; padding: 2px 0">Reporter:</th>
<td style="padding: 0px; border-collapse: collapse; font: normal 14px/20px Arial, sans-serif; padding: 2px 0 2px 5px; vertical-align: top"> <a class="user-hover" rel="ian@iay.org.uk" id="email_ian@iay.org.uk" href="https://issues.shibboleth.net/jira/secure/ViewProfile.jspa?name=ian%40iay.org.uk" style="color:#0052cc;; color: #3b73af; text-decoration: none">Ian Young</a> </td>
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<td class="text-paragraph-pattern-container mobile-resize-text " style="padding: 0px; border-collapse: collapse; padding: 0 0 10px 0"> <p style="margin-top:0;margin-bottom:10px;; margin: 10px 0 0 0; margin-top: 0">There are use cases of the MDA framework such as federation metadata processing which are almost embarrassingly parallel, for example when thousands of SAML metadata items are passed through a series of stages which require no interaction between the items. It would make sense to add a stage which allows this to be parallelised explicitly.</p> <p style="margin-top:0;margin-bottom:10px;; margin: 10px 0 0 0">This would most obviously have a <tt>Pipeline</tt> property, an <tt>ExecutorService</tt> and some kind of partitioning strategy determining how many tasks to create.</p> <p style="margin-top:0;margin-bottom:10px;; margin: 10px 0 0 0">Minimising copies of the items is important. So partitioning would have to work as:</p>
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<li>Figure out how many tasks to create</li>
<li>Create that many new empty collections of items</li>
<li>Partition the existing collection into those new collections (without copying the items)</li>
<li>Clear the existing collection (the new collections now have the only references to the items)</li>
<li>Create and submit tasks to run the pipeline on each of the new collections (results in a happens-before relation and the items are no longer "ours")</li>
<li>Wait for each task's <tt>Future</tt> in order, and return the resulting collection's items to the original collection when it is done</li>
<li>This should result in the same item ordering as in the original collection, assuming that the pipeline doesn't reorder or delete items (it's fine for it to do so, though)</li>
</ul> <p style="margin-top:0;margin-bottom:10px;; margin: 10px 0 0 0">I'm fairly sure that the guarantees we get from an <tt>ExecutorService</tt> and from <tt>Future</tt> mean that this is thread safe even if the item classes aren't.</p> <p style="margin-top:0;margin-bottom:10px;; margin: 10px 0 0 0">The critical issues are choice of <tt>ExecutorService</tt> (which determines how many threads will be used) and the choice of how many tasks to use (which should be a bigger number, but not too big). There are probably some decent heuristics around this, but they interact.</p> </td>
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