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105 lines
4.6 KiB
HTML
105 lines
4.6 KiB
HTML
<?xml version="1.0" encoding="UTF-8" standalone="no"?>
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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<html xmlns="http://www.w3.org/1999/xhtml">
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
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<title>Exclusive Database Handles</title>
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<link rel="stylesheet" href="gettingStarted.css" type="text/css" />
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<meta name="generator" content="DocBook XSL Stylesheets V1.73.2" />
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<link rel="start" href="index.html" title="Getting Started with Berkeley DB Transaction Processing" />
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<link rel="up" href="txnconcurrency.html" title="Chapter 4. Concurrency" />
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<link rel="prev" href="txn_ccursor.html" title="Transactional Cursors and Concurrent Applications" />
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<link rel="next" href="readmodifywrite.html" title="Read/Modify/Write" />
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</head>
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<body>
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<div xmlns="" class="navheader">
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<div class="libver">
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<p>Library Version 11.2.5.3</p>
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</div>
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<table width="100%" summary="Navigation header">
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<tr>
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<th colspan="3" align="center">Exclusive Database Handles</th>
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</tr>
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<tr>
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<td width="20%" align="left"><a accesskey="p" href="txn_ccursor.html">Prev</a> </td>
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<th width="60%" align="center">Chapter 4. Concurrency</th>
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<td width="20%" align="right"> <a accesskey="n" href="readmodifywrite.html">Next</a></td>
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</tr>
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</table>
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<hr />
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</div>
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<div class="sect1" lang="en" xml:lang="en">
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<div class="titlepage">
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<div>
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<div>
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<h2 class="title" style="clear: both"><a id="exclusivelock"></a>Exclusive Database Handles</h2>
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</div>
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</div>
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</div>
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<p>
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In some cases, concurrent applications can benefit from
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occasionally granting exclusive access to the entire
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database to a single database handle. This is
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desirable when a thread will perform an operation that
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touches all or most of the pages in a database.
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</p>
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<p>
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To configure a handle to have exclusive access to a database,
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you give it a single write lock to the entire database. This
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causes all other threads to block when they attempt to gain a
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read or write lock to any part of that database.
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</p>
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<p>
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The exclusive lock allows for improved throughput
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because the handle will not attempt to acquire any further
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locks once it has the exclusive write lock. It will also never
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be blocked waiting for a lock, and there is no possibility of
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a deadlock/retry cycle.
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</p>
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<p>
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Note that an exclusive database handle can only have one
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transaction active for it at a time.
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</p>
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<p>
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To configure a database handle with an exclusive lock, you
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use the
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<span>
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<code class="methodname">Db::set_lk_exclusive()</code>
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method before you open the database handle. Setting a
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value of <code class="literal">0</code> to this method means that
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the handle open operation will block until it can obtain
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the exclusive lock. A non-zero value means that if the
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method cannot obtain the exclusive lock immediately when
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the handle is opened, the open operation will exit with a
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<code class="literal">DB_LOCK_NOTGRANTED</code> error return.
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</span>
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</p>
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<p>
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Once configured and opened, a handled configured with an
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exclusive database lock will hold that lock until the handle
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is closed.
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</p>
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</div>
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<div class="navfooter">
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<hr />
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<table width="100%" summary="Navigation footer">
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<tr>
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<td width="40%" align="left"><a accesskey="p" href="txn_ccursor.html">Prev</a> </td>
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<td width="20%" align="center">
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<a accesskey="u" href="txnconcurrency.html">Up</a>
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</td>
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<td width="40%" align="right"> <a accesskey="n" href="readmodifywrite.html">Next</a></td>
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</tr>
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<tr>
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<td width="40%" align="left" valign="top">Transactional Cursors and Concurrent Applications </td>
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<td width="20%" align="center">
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<a accesskey="h" href="index.html">Home</a>
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</td>
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<td width="40%" align="right" valign="top"> Read/Modify/Write</td>
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</tr>
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</table>
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</div>
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</body>
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</html>
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