89 lines
5.2 KiB
HTML
89 lines
5.2 KiB
HTML
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<meta name="DC.Title" content="Checkpoint processing with save-while-active" />
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<title>Checkpoint processing with save-while-active</title>
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<body id="rzaiu327"><a name="rzaiu327"><!-- --></a>
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<!-- Java sync-link --><script language="Javascript" src="../rzahg/synch.js" type="text/javascript"></script>
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<h1 class="topictitle1">Checkpoint processing with save-while-active</h1>
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<div><div class="section"> <p>Checkpoint processing occurs after the server determines exactly
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which objects it will save for a particular library. If the save-while-active
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request is for multiple libraries, then the server performs checkpoint processing
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for all libraries in the save request.</p>
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<p>Checkpoint processing does not
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require that the server maintain two complete copies of the objects you are
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saving. The server only maintains two copies of the pages of the object that
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the applications are changing while you are performing the save. The more
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pages that applications change for an object during the save-while-active
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request, the greater the storage requirement for the object. After the server
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completes checkpoint processing to create the checkpoint image of the page,
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performance decreases slightly for the first update to a page. The performance
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impact varies depending on the disk type, available disk storage, and processor
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model. Further updates to the same changed page do not require any additional
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processing with respect to the checkpoint version of the page.</p>
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<div class="p">The
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following figure shows how the server maintains a checkpoint image of an object
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during a save-while-active operation. The shaded parts of the diagram represent
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the checkpoint version of the object. <span>An explanation of the steps follows
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the figure.</span> <div class="fignone" id="rzaiu327__swashdw"><a name="rzaiu327__swashdw"><!-- --></a><span class="figcap">Figure 1. Server management of updates to
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objects after checkpoint processing is complete</span><br /><img src="rv2w419.gif" alt="Checkpoint processing illustration" /><br /></div>
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</div>
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<p>The figure above shows a timeline with T1 — T5:</p>
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</div>
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<ol><li class="stepexpand"><span>Time T1 is the save preprocessing phase of the save-while-active
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operation. The object reaches a checkpoint at the end of time T1.</span></li>
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<li class="stepexpand"><span></span> Time T2 shows an update to the object, referred to
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as C1. The update occurs while the save-while-active request saves the object
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to the media.
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<ol type="a"><li>An application makes a request to update C1.</li>
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<li>The server first makes a copy of the original page.</li>
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<li>The applications make the change to the object.</li>
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</ol>
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<p>The original page copied is then part of the checkpoint image for the object.</p>
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</li>
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<li class="stepexpand"><span>Time T3 shows that the object received two additional changes,
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C2 and C3. Any additional change requests that are made to the pages of the
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object already changed for C1, C2, or C3 do not require any additional processing.
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At the end of time T3, the save-while-active request has completely saved
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the object to the media.</span></li>
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<li class="stepexpand"><span>Time T4 shows that the server no longer maintains copied pages
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for the checkpoint image of the object because the server no longer needs
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them.</span></li>
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<li class="stepexpand"><span>Time T5 shows the object on the server has the C1, C2, and C3 changes.
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But the copy, or image, of the object saved to the media does not contain
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those changes.</span></li>
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</ol>
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<div class="section"></div>
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</div>
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<div>
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<div class="familylinks">
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<div class="parentlink"><strong>Parent topic:</strong> <a href="rzaiurzaiu310.htm">Save-while-active function</a></div>
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</div>
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<div class="relconcepts"><strong>Related concepts</strong><br />
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<div><a href="rzaiucommitoverview.htm">Commitment control with save-while-active</a></div>
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</div>
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</div>
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