mirror of
https://github.com/berkeleydb/libdb.git
synced 2024-11-16 17:16:25 +00:00
106 lines
4.6 KiB
HTML
106 lines
4.6 KiB
HTML
|
<?xml version="1.0" encoding="UTF-8" standalone="no"?>
|
|||
|
|
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
|
|||
|
|
<html xmlns="http://www.w3.org/1999/xhtml">
|
|||
|
|
<head>
|
|||
|
|
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
|
|||
|
|
<title>Exclusive Database Handles</title>
|
|||
|
|
<link rel="stylesheet" href="gettingStarted.css" type="text/css" />
|
|||
|
|
<meta name="generator" content="DocBook XSL Stylesheets V1.73.2" />
|
|||
|
|
<link rel="start" href="index.html" title="Getting Started with Berkeley DB Transaction Processing" />
|
|||
|
|
<link rel="up" href="txnconcurrency.html" title="Chapter 4. Concurrency" />
|
|||
|
|
<link rel="prev" href="txn_ccursor.html" title="Transactional Cursors and Concurrent Applications" />
|
|||
|
|
<link rel="next" href="readmodifywrite.html" title="Read/Modify/Write" />
|
|||
|
|
</head>
|
|||
|
|
<body>
|
|||
|
|
<div xmlns="" class="navheader">
|
|||
|
|
<div class="libver">
|
|||
|
|
<p>Library Version 11.2.5.3</p>
|
|||
|
|
</div>
|
|||
|
|
<table width="100%" summary="Navigation header">
|
|||
|
|
<tr>
|
|||
|
|
<th colspan="3" align="center">Exclusive Database Handles</th>
|
|||
|
|
</tr>
|
|||
|
|
<tr>
|
|||
|
|
<td width="20%" align="left"><a accesskey="p" href="txn_ccursor.html">Prev</a> </td>
|
|||
|
|
<th width="60%" align="center">Chapter 4. Concurrency</th>
|
|||
|
|
<td width="20%" align="right"> <a accesskey="n" href="readmodifywrite.html">Next</a></td>
|
|||
|
|
</tr>
|
|||
|
|
</table>
|
|||
|
|
<hr />
|
|||
|
|
</div>
|
|||
|
|
<div class="sect1" lang="en" xml:lang="en">
|
|||
|
|
<div class="titlepage">
|
|||
|
|
<div>
|
|||
|
|
<div>
|
|||
|
|
<h2 class="title" style="clear: both"><a id="exclusivelock"></a>Exclusive Database Handles</h2>
|
|||
|
|
</div>
|
|||
|
|
</div>
|
|||
|
|
</div>
|
|||
|
|
<p>
|
|||
|
|
In some cases, concurrent applications can benefit from
|
|||
|
|
occasionally granting exclusive access to the entire
|
|||
|
|
database to a single database handle. This is
|
|||
|
|
desirable when a thread will perform an operation that
|
|||
|
|
touches all or most of the pages in a database.
|
|||
|
|
</p>
|
|||
|
|
<p>
|
|||
|
|
To configure a handle to have exclusive access to a database,
|
|||
|
|
you give it a single write lock to the entire database. This
|
|||
|
|
causes all other threads to block when they attempt to gain a
|
|||
|
|
read or write lock to any part of that database.
|
|||
|
|
</p>
|
|||
|
|
<p>
|
|||
|
|
The exclusive lock allows for improved throughput
|
|||
|
|
because the handle will not attempt to acquire any further
|
|||
|
|
locks once it has the exclusive write lock. It will also never
|
|||
|
|
be blocked waiting for a lock, and there is no possibility of
|
|||
|
|
a deadlock/retry cycle.
|
|||
|
|
</p>
|
|||
|
|
<p>
|
|||
|
|
Note that an exclusive database handle can only have one
|
|||
|
|
transaction active for it at a time.
|
|||
|
|
</p>
|
|||
|
|
<p>
|
|||
|
|
To configure a database handle with an exclusive lock, you
|
|||
|
|
use the
|
|||
|
|
<span>
|
|||
|
|
|
|||
|
|
<code class="methodname">Db::set_lk_exclusive()</code>
|
|||
|
|
method before you open the database handle. Setting a
|
|||
|
|
value of <code class="literal">0</code> to this method means that
|
|||
|
|
the handle open operation will block until it can obtain
|
|||
|
|
the exclusive lock. A non-zero value means that if the
|
|||
|
|
method cannot obtain the exclusive lock immediately when
|
|||
|
|
the handle is opened, the open operation will exit with a
|
|||
|
|
<code class="literal">DB_LOCK_NOTGRANTED</code> error return.
|
|||
|
|
</span>
|
|||
|
|
|
|||
|
|
</p>
|
|||
|
|
<p>
|
|||
|
|
Once configured and opened, a handled configured with an
|
|||
|
|
exclusive database lock will hold that lock until the handle
|
|||
|
|
is closed.
|
|||
|
|
</p>
|
|||
|
|
</div>
|
|||
|
|
<div class="navfooter">
|
|||
|
|
<hr />
|
|||
|
|
<table width="100%" summary="Navigation footer">
|
|||
|
|
<tr>
|
|||
|
|
<td width="40%" align="left"><a accesskey="p" href="txn_ccursor.html">Prev</a> </td>
|
|||
|
|
<td width="20%" align="center">
|
|||
|
|
<a accesskey="u" href="txnconcurrency.html">Up</a>
|
|||
|
|
</td>
|
|||
|
|
<td width="40%" align="right"> <a accesskey="n" href="readmodifywrite.html">Next</a></td>
|
|||
|
|
</tr>
|
|||
|
|
<tr>
|
|||
|
|
<td width="40%" align="left" valign="top">Transactional Cursors and Concurrent Applications </td>
|
|||
|
|
<td width="20%" align="center">
|
|||
|
|
<a accesskey="h" href="index.html">Home</a>
|
|||
|
|
</td>
|
|||
|
|
<td width="40%" align="right" valign="top"> Read/Modify/Write</td>
|
|||
|
|
</tr>
|
|||
|
|
</table>
|
|||
|
|
</div>
|
|||
|
|
</body>
|
|||
|
|
</html>
|