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             <h1 class="title">Jena Transactions API</h1>


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     <h2 class="h6 sticky-top m-0 p-2 bg-body-tertiary">On this page</h2>
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   <ul>
     <li><a href="#api-for-transactions">API for Transactions</a>
       <ul>
         <li><a href="#read-transactions">Read transactions</a></li>
         <li><a href="#write-transactions">Write transactions</a></li>
       </ul>
     </li>
     <li><a href="#types-modes-promotion">Transaction Types, Modes and Promotion.</a></li>
     <li><a href="#multi-threaded-use">Multi-threaded use</a></li>
     <li><a href="#multi-jvm">Multi JVM</a></li>
   </ul>
 </nav>
   </aside>
   <article class="flex-column me-lg-4">
     <ul>
 <li><a href="#api-for-transactions">API for Transactions</a>
 <ul>
 <li><a href="#read-transactions">Read transactions</a></li>
 <li><a href="#write-transactions">Write transactions</a></li>
 <li><a href="#types-modes-promotion">Transaction promotion</a></li>
 </ul>
 </li>
 <li><a href="txn.html">Txn</a> - A higher level API to transactions</li>
 </ul>
 <h2 id="api-for-transactions">API for Transactions</h2>
 <p>This page describes the basic transaction API in Jena (3.1.0 and later).</p>
 <p>There is also a <a href="txn.html">higher-level API</a> useful in many situations
 but sometimes it is necessary to use the basic transaction API described here.</p>
 <h3 id="read-transactions">Read transactions</h3>
 <p>These are used for SPARQL queries and code using the Jena API
 actions that do not change the data.  The general pattern is:</p>
 <div class="highlight"><pre tabindex="0" style="background-color:#f8f8f8;-moz-tab-size:4;-o-tab-size:4;tab-size:4;"><code class="language-java" data-lang="java"><span style="display:flex;"><span>dataset<span style="color:#666">.</span><span style="color:#b44">begin</span><span style="color:#666">(</span>ReadWrite<span style="color:#666">.</span><span style="color:#b44">READ</span><span style="color:#666">)</span> <span style="color:#666">;</span>
 </span></span><span style="display:flex;"><span><span style="color:#a2f;font-weight:bold">try</span> <span style="color:#666">{</span>
 </span></span><span style="display:flex;"><span>    <span style="color:#666">...</span>
 </span></span><span style="display:flex;"><span><span style="color:#666">}</span> <span style="color:#a2f;font-weight:bold">finally</span> <span style="color:#666">{</span> dataset<span style="color:#666">.</span><span style="color:#b44">end</span><span style="color:#666">()</span> <span style="color:#666">;</span> <span style="color:#666">}</span>
 </span></span></code></pre></div><p>The <code>dataset.end()</code> declares the end of the read transaction.  Applications may also call
 <code>dataset.commit()</code> or <code>dataset.abort()</code> which all have the same effect for a read transaction.</p>
 <p>This example has two queries - no updates between or during the queries will be seen by
 this code even if another thread commits changes in the lifetime of this transaction.</p>
 <div class="highlight"><pre tabindex="0" style="background-color:#f8f8f8;-moz-tab-size:4;-o-tab-size:4;tab-size:4;"><code class="language-java" data-lang="java"><span style="display:flex;"><span>Dataset dataset <span style="color:#666">=</span> <span style="color:#666">...</span> <span style="color:#666">;</span>
 </span></span><span style="display:flex;"><span>dataset<span style="color:#666">.</span><span style="color:#b44">begin</span><span style="color:#666">(</span>ReadWrite<span style="color:#666">.</span><span style="color:#b44">READ</span><span style="color:#666">)</span> <span style="color:#666">;</span>
 </span></span><span style="display:flex;"><span><span style="color:#a2f;font-weight:bold">try</span> <span style="color:#666">{</span>
 </span></span><span style="display:flex;"><span>    String qs1 <span style="color:#666">=</span> <span style="color:#b44">&#34;SELECT * {?s ?p ?o} LIMIT 10&#34;</span> <span style="color:#666">;</span>
 </span></span><span style="display:flex;"><span>    <span style="color:#a2f;font-weight:bold">try</span><span style="color:#666">(</span>QueryExecution qExec <span style="color:#666">=</span> QueryExecution<span style="color:#666">.</span><span style="color:#b44">create</span><span style="color:#666">(</span>qs1<span style="color:#666">,</span> dataset<span style="color:#666">))</span> <span style="color:#666">{</span>
 </span></span><span style="display:flex;"><span>        ResultSet rs <span style="color:#666">=</span> qExec<span style="color:#666">.</span><span style="color:#b44">execSelect</span><span style="color:#666">()</span> <span style="color:#666">;</span>
 </span></span><span style="display:flex;"><span>        ResultSetFormatter<span style="color:#666">.</span><span style="color:#b44">out</span><span style="color:#666">(</span>rs<span style="color:#666">)</span> <span style="color:#666">;</span>
 </span></span><span style="display:flex;"><span>    <span style="color:#666">}</span>
 </span></span><span style="display:flex;"><span>
 </span></span><span style="display:flex;"><span>    String qs2 <span style="color:#666">=</span> <span style="color:#b44">&#34;SELECT * {?s ?p ?o} OFFSET 10 LIMIT 10&#34;</span> <span style="color:#666">;</span>
 </span></span><span style="display:flex;"><span>    <span style="color:#a2f;font-weight:bold">try</span><span style="color:#666">(</span>QueryExecution qExec <span style="color:#666">=</span> QueryExecution<span style="color:#666">.</span><span style="color:#b44">create</span><span style="color:#666">(</span>qs2<span style="color:#666">,</span> dataset<span style="color:#666">))</span> <span style="color:#666">{</span>
 </span></span><span style="display:flex;"><span>        rs <span style="color:#666">=</span> qExec<span style="color:#666">.</span><span style="color:#b44">execSelect</span><span style="color:#666">()</span> <span style="color:#666">;</span>
 </span></span><span style="display:flex;"><span>        ResultSetFormatter<span style="color:#666">.</span><span style="color:#b44">out</span><span style="color:#666">(</span>rs<span style="color:#666">)</span> <span style="color:#666">;</span>
 </span></span><span style="display:flex;"><span>    <span style="color:#666">}</span>
 </span></span><span style="display:flex;"><span><span style="color:#666">}</span> <span style="color:#a2f;font-weight:bold">finally</span> <span style="color:#666">{</span> dataset<span style="color:#666">.</span><span style="color:#b44">end</span><span style="color:#666">()</span> <span style="color:#666">;</span> <span style="color:#666">}</span>
 </span></span></code></pre></div><h3 id="write-transactions">Write transactions</h3>
 <p>These are used for SPARQL queries, SPARQL updates and any Jena API
 actions that modify the data.  Beware that large <code>model.read</code>
 operations to change a dataset may consume large amounts of temporary space.</p>
 <p>The general pattern is:</p>
 <div class="highlight"><pre tabindex="0" style="background-color:#f8f8f8;-moz-tab-size:4;-o-tab-size:4;tab-size:4;"><code class="language-java" data-lang="java"><span style="display:flex;"><span>dataset<span style="color:#666">.</span><span style="color:#b44">begin</span><span style="color:#666">(</span>ReadWrite<span style="color:#666">.</span><span style="color:#b44">WRITE</span><span style="color:#666">)</span> <span style="color:#666">;</span>
 </span></span><span style="display:flex;"><span><span style="color:#a2f;font-weight:bold">try</span> <span style="color:#666">{</span>
 </span></span><span style="display:flex;"><span>    <span style="color:#666">...</span>
 </span></span><span style="display:flex;"><span>    dataset<span style="color:#666">.</span><span style="color:#b44">commit</span><span style="color:#666">()</span> <span style="color:#666">;</span>
 </span></span><span style="display:flex;"><span><span style="color:#666">}</span> <span style="color:#a2f;font-weight:bold">finally</span> <span style="color:#666">{</span>
 </span></span><span style="display:flex;"><span>    dataset<span style="color:#666">.</span><span style="color:#b44">end</span><span style="color:#666">()</span> <span style="color:#666">;</span>
 </span></span><span style="display:flex;"><span><span style="color:#666">}</span>
 </span></span></code></pre></div><p>The  <code>dataset.end()</code> will abort the transaction is there was no call to
 <code>dataset.commit()</code> or <code>dataset.abort()</code> inside the write transaction.</p>
 <p>Once <code>dataset.commit()</code> or <code>dataset.abort()</code> is called, the application
 needs to start a new transaction to perform further operations on the
 dataset.</p>
 <div class="highlight"><pre tabindex="0" style="background-color:#f8f8f8;-moz-tab-size:4;-o-tab-size:4;tab-size:4;"><code class="language-java" data-lang="java"><span style="display:flex;"><span>Dataset dataset <span style="color:#666">=</span> <span style="color:#666">...</span> <span style="color:#666">;</span>
 </span></span><span style="display:flex;"><span>dataset<span style="color:#666">.</span><span style="color:#b44">begin</span><span style="color:#666">(</span>TxnType<span style="color:#666">.</span><span style="color:#b44">WRITE</span><span style="color:#666">)</span> <span style="color:#666">;</span>
 </span></span><span style="display:flex;"><span>
 </span></span><span style="display:flex;"><span><span style="color:#a2f;font-weight:bold">try</span> <span style="color:#666">{</span>
 </span></span><span style="display:flex;"><span>    Model model <span style="color:#666">=</span> dataset<span style="color:#666">.</span><span style="color:#b44">getDefaultModel</span><span style="color:#666">()</span> <span style="color:#666">;</span>
 </span></span><span style="display:flex;"><span>    <span style="color:#080;font-style:italic">// API calls to a model in the dataset
 </span></span></span><span style="display:flex;"><span><span style="color:#080;font-style:italic"></span>
 </span></span><span style="display:flex;"><span>    <span style="color:#080;font-style:italic">// Make some changes via the model ...
 </span></span></span><span style="display:flex;"><span><span style="color:#080;font-style:italic"></span>    model<span style="color:#666">.</span><span style="color:#b44">add</span><span style="color:#666">(</span> <span style="color:#666">...</span> <span style="color:#666">)</span>
 </span></span><span style="display:flex;"><span>
 </span></span><span style="display:flex;"><span>    <span style="color:#080;font-style:italic">// A SPARQL query will see the new statement added.
 </span></span></span><span style="display:flex;"><span><span style="color:#080;font-style:italic"></span>    <span style="color:#a2f;font-weight:bold">try</span> <span style="color:#666">(</span>QueryExecution qExec <span style="color:#666">=</span> QueryExecution<span style="color:#666">.</span><span style="color:#b44">create</span><span style="color:#666">(</span>
 </span></span><span style="display:flex;"><span>         <span style="color:#b44">&#34;SELECT (count(?s) AS ?count) { ?s ?p ?o} LIMIT 10&#34;</span><span style="color:#666">,</span>
 </span></span><span style="display:flex;"><span>         dataset<span style="color:#666">))</span> <span style="color:#666">{</span>
 </span></span><span style="display:flex;"><span>        ResultSet rs <span style="color:#666">=</span> qExec<span style="color:#666">.</span><span style="color:#b44">execSelect</span><span style="color:#666">()</span> <span style="color:#666">;</span>
 </span></span><span style="display:flex;"><span>        ResultSetFormatter<span style="color:#666">.</span><span style="color:#b44">out</span><span style="color:#666">(</span>rs<span style="color:#666">)</span> <span style="color:#666">;</span>
 </span></span><span style="display:flex;"><span>    <span style="color:#666">}</span>
 </span></span><span style="display:flex;"><span>
 </span></span><span style="display:flex;"><span>    <span style="color:#080;font-style:italic">// ... perform a SPARQL Update
 </span></span></span><span style="display:flex;"><span><span style="color:#080;font-style:italic"></span>    String sparqlUpdateString <span style="color:#666">=</span> StrUtils<span style="color:#666">.</span><span style="color:#b44">strjoinNL</span><span style="color:#666">(</span>
 </span></span><span style="display:flex;"><span>        <span style="color:#b44">&#34;PREFIX . &lt;http://example/&gt;&#34;</span><span style="color:#666">,</span>
 </span></span><span style="display:flex;"><span>        <span style="color:#b44">&#34;INSERT { :s :p ?now } WHERE { BIND(now() AS ?now) }&#34;</span>
 </span></span><span style="display:flex;"><span>    <span style="color:#666">)</span> <span style="color:#666">;</span>
 </span></span><span style="display:flex;"><span>
 </span></span><span style="display:flex;"><span>    UpdateRequest request <span style="color:#666">=</span> UpdateFactory<span style="color:#666">.</span><span style="color:#b44">create</span><span style="color:#666">(</span>sparqlUpdateString<span style="color:#666">)</span> <span style="color:#666">;</span>
 </span></span><span style="display:flex;"><span>    UpdateExecution<span style="color:#666">.</span><span style="color:#b44">dataset</span><span style="color:#666">(</span>dataset<span style="color:#666">).</span><span style="color:#b44">update</span><span style="color:#666">(</span>request<span style="color:#666">).</span><span style="color:#b44">execute</span><span style="color:#666">()</span> <span style="color:#666">;</span>
 </span></span><span style="display:flex;"><span>
 </span></span><span style="display:flex;"><span>    <span style="color:#080;font-style:italic">// Finally, commit the transaction.
 </span></span></span><span style="display:flex;"><span><span style="color:#080;font-style:italic"></span>    dataset<span style="color:#666">.</span><span style="color:#b44">commit</span><span style="color:#666">()</span> <span style="color:#666">;</span>
 </span></span><span style="display:flex;"><span>    <span style="color:#080;font-style:italic">// Or call .abort()
 </span></span></span><span style="display:flex;"><span><span style="color:#080;font-style:italic"></span><span style="color:#666">}</span> <span style="color:#a2f;font-weight:bold">finally</span> <span style="color:#666">{</span>
 </span></span><span style="display:flex;"><span>    dataset<span style="color:#666">.</span><span style="color:#b44">end</span><span style="color:#666">()</span> <span style="color:#666">;</span>
 </span></span><span style="display:flex;"><span><span style="color:#666">}</span>
 </span></span></code></pre></div><h2 id="types-modes-promotion">Transaction Types, Modes and Promotion.</h2>
 <p>Transaction have a type (enum <code>TxnType</code>) and a mode (enum <code>ReadWrite</code>).
 <code>TxnType.READ</code> and <code>TxnType.Write</code> start the transaction in
 that mode and the mode is fixed for the transaction&rsquo;s lifetime. A <code>READ</code>
 transaction can never update the data of the transactional object it is
 acting on.</p>
 <p>Transactions can have type <code>TxnType.READ_PROMOTE</code> or
 <code>TxnType.READ_COMMITTED_PROMOTE</code>. These start in mode <code>READ</code> but can
 become mode <code>WRITE</code>, either implicitly by attempting an update, or
 explicitly by calling <code>promote</code>.</p>
 <p><code>READ_PROMOTE</code> only succeeds if no writer has made any changes since
 this transaction started. It gives full isolation.</p>
 <p><code>READ_COMMITTED_PROMOTE</code> always succeeds because it changes the view of
 the data to include any changes made up to that point (it is &ldquo;read
 committed&rdquo;). Applications should be aware that data they have read up
 until the point of promotion (the first call or <code>.promote</code> or first
 update made) may now be invalid. For this reason, <code>READ_PROMOTE</code> is preferred.</p>
 <p><code>begin()</code>, the method with no arguments, is equivalent to
 <code>begin(TxnType.READ_PROMOTE)</code>.</p>
 <h2 id="multi-threaded-use">Multi-threaded use</h2>
 <p>Each dataset object has one transaction active at a time per thread.
 A dataset object can be used by different threads, with independent transactions.</p>
 <p>The usual idiom within multi-threaded applications is to have
 one dataset, and so there is one transaction per thread.</p>
 <p>Either:</p>
 <div class="highlight"><pre tabindex="0" style="background-color:#f8f8f8;-moz-tab-size:4;-o-tab-size:4;tab-size:4;"><code class="language-java" data-lang="java"><span style="display:flex;"><span><span style="color:#080;font-style:italic">// Create a dataset and keep it globally.
 </span></span></span><span style="display:flex;"><span><span style="color:#080;font-style:italic"></span><span style="color:#a2f;font-weight:bold">static</span> Dataset dataset <span style="color:#666">=</span> TDBFactory<span style="color:#666">.</span><span style="color:#b44">createDataset</span><span style="color:#666">(</span>location<span style="color:#666">)</span> <span style="color:#666">;</span>
 </span></span></code></pre></div><p>Thread 1:</p>
 <div class="highlight"><pre tabindex="0" style="background-color:#f8f8f8;-moz-tab-size:4;-o-tab-size:4;tab-size:4;"><code class="language-java" data-lang="java"><span style="display:flex;"><span>dataset<span style="color:#666">.</span><span style="color:#b44">begin</span><span style="color:#666">(</span>TxnType<span style="color:#666">.</span><span style="color:#b44">WRITE</span><span style="color:#666">)</span> <span style="color:#666">;</span>
 </span></span><span style="display:flex;"><span><span style="color:#a2f;font-weight:bold">try</span> <span style="color:#666">{</span>
 </span></span><span style="display:flex;"><span>    <span style="color:#666">...</span>
 </span></span><span style="display:flex;"><span>    dataset<span style="color:#666">.</span><span style="color:#b44">commit</span><span style="color:#666">()</span> <span style="color:#666">;</span>
 </span></span><span style="display:flex;"><span><span style="color:#666">}</span> <span style="color:#a2f;font-weight:bold">finally</span> <span style="color:#666">{</span> dataset<span style="color:#666">.</span><span style="color:#b44">end</span><span style="color:#666">()</span> <span style="color:#666">;</span> <span style="color:#666">}</span>
 </span></span></code></pre></div><p>Thread 2:</p>
 <div class="highlight"><pre tabindex="0" style="background-color:#f8f8f8;-moz-tab-size:4;-o-tab-size:4;tab-size:4;"><code class="language-java" data-lang="java"><span style="display:flex;"><span>dataset<span style="color:#666">.</span><span style="color:#b44">begin</span><span style="color:#666">(</span>TxnType<span style="color:#666">.</span><span style="color:#b44">READ</span><span style="color:#666">)</span> <span style="color:#666">;</span>
 </span></span><span style="display:flex;"><span><span style="color:#a2f;font-weight:bold">try</span> <span style="color:#666">{</span>
 </span></span><span style="display:flex;"><span>    <span style="color:#666">...</span>
 </span></span><span style="display:flex;"><span><span style="color:#666">}</span> <span style="color:#a2f;font-weight:bold">finally</span> <span style="color:#666">{</span> dataset<span style="color:#666">.</span><span style="color:#b44">end</span><span style="color:#666">()</span> <span style="color:#666">;</span> <span style="color:#666">}</span>
 </span></span></code></pre></div><p>It is possible (in TDB) to create different dataset objects to the same location.</p>
 <p>Thread 1:</p>
 <div class="highlight"><pre tabindex="0" style="background-color:#f8f8f8;-moz-tab-size:4;-o-tab-size:4;tab-size:4;"><code class="language-java" data-lang="java"><span style="display:flex;"><span>Dataset dataset <span style="color:#666">=</span> TDBFactory<span style="color:#666">.</span><span style="color:#b44">createDataset</span><span style="color:#666">(</span>location<span style="color:#666">)</span> <span style="color:#666">;</span>
 </span></span><span style="display:flex;"><span>dataset<span style="color:#666">.</span><span style="color:#b44">begin</span><span style="color:#666">(</span>TxnType<span style="color:#666">.</span><span style="color:#b44">WRITE</span><span style="color:#666">)</span> <span style="color:#666">;</span>
 </span></span><span style="display:flex;"><span><span style="color:#a2f;font-weight:bold">try</span> <span style="color:#666">{</span>
 </span></span><span style="display:flex;"><span>    <span style="color:#666">...</span>
 </span></span><span style="display:flex;"><span>    dataset<span style="color:#666">.</span><span style="color:#b44">commit</span><span style="color:#666">()</span> <span style="color:#666">;</span>
 </span></span><span style="display:flex;"><span><span style="color:#666">}</span> <span style="color:#a2f;font-weight:bold">finally</span> <span style="color:#666">{</span> dataset<span style="color:#666">.</span><span style="color:#b44">end</span><span style="color:#666">()</span> <span style="color:#666">;</span> <span style="color:#666">}</span>
 </span></span></code></pre></div><p>Thread 2:</p>
 <div class="highlight"><pre tabindex="0" style="background-color:#f8f8f8;-moz-tab-size:4;-o-tab-size:4;tab-size:4;"><code class="language-java" data-lang="java"><span style="display:flex;"><span>Dataset dataset <span style="color:#666">=</span> TDBFactory<span style="color:#666">.</span><span style="color:#b44">createDataset</span><span style="color:#666">(</span>location<span style="color:#666">)</span> <span style="color:#666">;</span>
 </span></span><span style="display:flex;"><span>dataset<span style="color:#666">.</span><span style="color:#b44">begin</span><span style="color:#666">(</span>TxnType<span style="color:#666">.</span><span style="color:#b44">READ</span><span style="color:#666">)</span> <span style="color:#666">;</span>
 </span></span><span style="display:flex;"><span><span style="color:#a2f;font-weight:bold">try</span> <span style="color:#666">{</span>
 </span></span><span style="display:flex;"><span>    <span style="color:#666">...</span>
 </span></span><span style="display:flex;"><span><span style="color:#666">}</span> <span style="color:#a2f;font-weight:bold">finally</span> <span style="color:#666">{</span> dataset<span style="color:#666">.</span><span style="color:#b44">end</span><span style="color:#666">()</span> <span style="color:#666">;</span> <span style="color:#666">}</span>
 </span></span></code></pre></div><p>Each thread has a separate <code>dataset</code> object; these safely share the
 same storage and have independent transactions.</p>
 <h2 id="multi-jvm">Multi JVM</h2>
 <p>Multiple applications, running in multiple JVMs, using the same file
 databases is not 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.  From 1.1.0 onwards TDB
 includes automatic prevention against multi-JVM which prevents this
 under most circumstances.</p>
 <p>Use our <a href="../fuseki2/">Fuseki</a> component to provide a
 database server for multiple applications. 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>.</p>

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     <nav id="TableOfContents">
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     <li><a href="#api-for-transactions">API for Transactions</a>
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