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Posted to commits@jena.apache.org by bu...@apache.org on 2014/06/19 09:48:42 UTC
svn commit: r912989 - in /websites/staging/jena/trunk/content: ./
documentation/tdb/faqs.html
Author: buildbot
Date: Thu Jun 19 07:48:42 2014
New Revision: 912989
Log:
Staging update by buildbot for jena
Added:
websites/staging/jena/trunk/content/documentation/tdb/faqs.html
Modified:
websites/staging/jena/trunk/content/ (props changed)
Propchange: websites/staging/jena/trunk/content/
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Added: websites/staging/jena/trunk/content/documentation/tdb/faqs.html
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--- websites/staging/jena/trunk/content/documentation/tdb/faqs.html (added)
+++ websites/staging/jena/trunk/content/documentation/tdb/faqs.html Thu Jun 19 07:48:42 2014
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+<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
+<html>
+<head>
+<!--
+
+ Licensed to the Apache Software Foundation (ASF) under one or more
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+ <title>Apache Jena - TDB FAQs</title>
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+</nav>
+
+
+<div class="container">
+ <div class="row">
+ <div class="col-md-12">
+ <div id="breadcrumbs"></div>
+ <h1 class="title">TDB FAQs</h1>
+ <h2 id="faqs">FAQs</h2>
+<ul>
+<li><a href="#transactions">Does TDB support Transactions?</a></li>
+<li><a href="#multi-jvm">Can I share a TDB dataset between multiple applications?</a></li>
+<li><a href="#impossibly-large-object">What is the "Impossibly Large Object" exception?</a></li>
+</ul>
+<p><a name="transactions"></a></p>
+<h2 id="does-tdb-support-transactions">Does TDB support transactions?</h2>
+<p>Yes, TDB provides
+<a href="http://en.wikipedia.org/wiki/Isolation_(database_systems)#SERIALIZABLE">Serializable</a>
+transactions, the highest
+<a href="http://en.wikipedia.org/wiki/Isolation_(database_systems)">isolation level</a>.</p>
+<p>Using transactions is <strong>strongly</strong> recommended as they help prevent data corruption
+from unexpected process termination and system crashes as well as data corruption that
+can otherwise occur from non-transactional use of TDB.</p>
+<p>Please see the <a href="tdb_transactions.html">transactions</a> documentation for how to use TDB
+transactionally.</p>
+<p><a name="multi-jvm"></a></p>
+<h2 id="can-i-share-a-tdb-dataset-between-multiple-applications">Can I share a TDB dataset between multiple applications?</h2>
+<p>Multiple applications, running in multiple JVMs, using the same
+file databases is <strong>not</strong> supported and has a high risk of data corruption. Once corrupted a database cannot be repaired
+and must be rebuilt from the original source data. Therefore there <strong>must</strong> be a single JVM
+controlling the database directory and files.</p>
+<p>If you wish to share a TDB dataset between applications use our <a href="../serving_data/">Fuseki</a> component which provides a
+database server. Fuseki supports <a href="http://www.w3.org/TR/sparql11-query/">SPARQL Query</a>,
+<a href="http://www.w3.org/TR/sparql11-update/">SPARQL Update</a> and the <a href="http://www.w3.org/TR/sparql11-http-rdf-update/">SPARQL Graph Store protocol</a>.
+Applications should be written in terms of these protocols using the relevant Jena APIs, this has the added benefit of making your
+applications portable to another SPARQL backend should you ever need to.</p>
+<p><a name="impossibly-large-object"></a></p>
+<h2 id="what-is-the-impossibly-large-object-exception">What is the "Impossibly Large Object" exception?</h2>
+<p>The "Impossibly Large Object" exception is an exception that occurs when part of your TDB dataset has become corrupted. It may
+only affect a small section of your dataset so may only occur intermittently depending on your queries. A query that touches
+the entirety of the dataset e.g.</p>
+<div class="codehilite"><pre><span class="n">SELECT</span> <span class="o">*</span> <span class="n">WHERE</span> <span class="p">{</span> <span class="p">{</span> ?<span class="n">s</span> ?<span class="n">p</span> ?<span class="n">o</span> <span class="p">}</span> <span class="n">UNION</span> <span class="p">{</span> <span class="n">GRAPH</span> ?<span class="n">g</span> <span class="p">{</span> ?<span class="n">s</span> ?<span class="n">p</span> ?<span class="n">o</span> <span class="p">}</span> <span class="p">}</span> <span class="p">}</span>
+</pre></div>
+
+
+<p>Will always experience this exception. The corruption may have happened at any time in the past and once it has happened there
+is no way to repair it. Corrupted datasets will need to be rebuilt from the original source data, this is why we <strong>strongly</strong>
+recommend you use <a href="tdb_transactions.html">transactions</a> since this protects your dataset against corruption.</p>
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