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| <div class="ind"><!-- End Header --><a id="pessimisticlock" name="pessimisticlock"></a><a id="TLJPA668" name="TLJPA668"></a> |
| <hr /> |
| <div class="refsect1"> |
| <h2 class="refsect1"><font face="arial, helvetica, sans-serif" color="#330099">pessimistic-lock</font></h2> |
| <p>Use <code>eclipselink.pessimistic-lock</code> to specify if EclipseLink uses pessimistic locking.</p> |
| <a id="sthref646" name="sthref646"></a> |
| <p><strong><br /><span class="refsubsect">Values</span></strong></p> |
| <p><a href="#CIHDEEDF">Table 4-25</a> describes this query hint's valid values.</p> |
| <div class="tblhruleformalwide"><a id="TLJPA669" name="TLJPA669"></a><a id="sthref647" name="sthref647"></a><a id="CIHDEEDF" name="CIHDEEDF"></a> |
| <p><strong><em><font face="arial, helvetica, sans-serif">Table 4-25 Valid Values for org.eclipse.persistence.config.PessimisticLock</font></em></strong></p> |
| <table class="HRuleFormalWide" title="Valid Values for org.eclipse.persistence.config.PessimisticLock" summary="Valid Values for this query hint" dir="ltr" border="1" width="100%" frame="hsides" rules="rows" cellpadding="3" cellspacing="0"> |
| <col width="29%" /> |
| <col width="*" /> |
| <thead> |
| <tr align="left" valign="top"> |
| <th align="left" valign="bottom" id="r1c1-t36"><font face="Arial, Helvetica, sans-serif"><strong>Value</strong></font></th> |
| <th align="left" valign="bottom" id="r1c2-t36"><font face="Arial, Helvetica, sans-serif"><strong>Description</strong></font></th> |
| </tr> |
| </thead> |
| <tbody> |
| <tr align="left" valign="top"> |
| <td align="left" id="r2c1-t36" headers="r1c1-t36"> |
| <p><code>NoLock</code></p> |
| </td> |
| <td align="left" headers="r2c1-t36 r1c2-t36"> |
| <p>(Default) Do not use pessimistic locking.</p> |
| </td> |
| </tr> |
| <tr align="left" valign="top"> |
| <td align="left" id="r3c1-t36" headers="r1c1-t36"> |
| <p><code>Lock</code></p> |
| </td> |
| <td align="left" headers="r3c1-t36 r1c2-t36"> |
| <p>EclipseLink issues <code>SELECT .... FOR UPDATE</code> statements.</p> |
| </td> |
| </tr> |
| <tr align="left" valign="top"> |
| <td align="left" id="r4c1-t36" headers="r1c1-t36"> |
| <p><code>LockNoWait</code></p> |
| </td> |
| <td align="left" headers="r4c1-t36 r1c2-t36"> |
| <p>EclipseLink issues <code>SELECT .... FOR UPDATE NO WAIT</code> statements.</p> |
| </td> |
| </tr> |
| </tbody> |
| </table> |
| <br /></div> |
| <!-- class="tblhruleformalwide" --> |
| <a id="sthref648" name="sthref648"></a> |
| <p><strong><br /><span class="refsubsect">Usage</span></strong></p> |
| <p>The primary advantage of using pessimistic locking is that you are assured, once the lock is obtained, of a successful edit. This is desirable in highly concurrent applications in which optimistic locking may cause too many optimistic locking errors.</p> |
| <p>One drawback of pessimistic locking is that it requires additional database resources, requiring the database transaction and connection to be maintained for the duration of the edit. Pessimistic locking may also cause deadlocks and lead to concurrency issues.</p> |
| <a id="sthref649" name="sthref649"></a> |
| <p><strong><br /><span class="refsubsect">Examples</span></strong></p> |
| <p><a href="#CIHGEJFF">Example 4-50</a> shows how to use this hint in a JPA query.</p> |
| <div class="example"><a id="CIHGEJFF" name="CIHGEJFF"></a><a id="TLJPA670" name="TLJPA670"></a> |
| <p><strong><em><font face="arial, helvetica, sans-serif">Example 4-50 Using pessimistic-lock in a JPA Query</font></em></strong></p> |
| <pre xml:space="preserve" class="oac_no_warn"> |
| import org.eclipse.persistence.config.PessimisticLock; |
| import org.eclipse.persistence.config.QueryHints; |
| query.setHint(QueryHints.PESSIMISTIC_LOCK, PessimisticLock.LockNoWait); |
| </pre></div> |
| <!-- class="example" --> |
| <p><a href="#CIHIAFGH">Example 4-51</a> shows how to use this hint with the <code>@QueryHint</code> annotation.</p> |
| <div class="example"><a id="CIHIAFGH" name="CIHIAFGH"></a><a id="TLJPA671" name="TLJPA671"></a> |
| <p><strong><em><font face="arial, helvetica, sans-serif">Example 4-51 Using pessimistic-lock in a @QueryHint Annotation</font></em></strong></p> |
| <pre xml:space="preserve" class="oac_no_warn"> |
| import org.eclipse.persistence.config.PessimisticLock; |
| import org.eclipse.persistence.config.QueryHints; |
| @QueryHint(name=QueryHints.PESSIMISTIC_LOCK, value=PessimisticLock.LockNoWait); |
| |
| </pre></div> |
| <!-- class="example" --> |
| <a id="sthref650" name="sthref650"></a> |
| <p><strong><br /><span class="refsubsect">See Also</span></strong></p> |
| <p>For more information, see:</p> |
| <ul> |
| <li> |
| <p>EclipseLink Examples<br /> |
| <code><a href="http://wiki.eclipse.org/EclipseLink/Examples/JPA/PessimisticLocking">http://wiki.eclipse.org/EclipseLink/Examples/JPA/PessimisticLocking</a></code></p> |
| </li> |
| <li> |
| <p>"Scaling EclipseLink Applications in Clusters" in <em>Solutions Guide for EclispeLink</em></p> |
| </li> |
| <li> |
| <p>"Understanding Queries" in <em>Understanding EclipseLink</em></p> |
| </li> |
| <li> |
| <p>"Building Blocks of a EclipseLink Project" in <em>Understanding EclipseLink</em></p> |
| </li> |
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