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<th width="60%" align="center">Chapter 2.
The DB Handle
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<div class="sect1" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h2 class="title" style="clear: both"><a id="dbset_lk_exclusive"></a>DB->set_lk_exclusive()</h2>
</div>
</div>
</div>
<pre class="programlisting">#include <db.h>
int
DB->set_lk_exclusive(DB *db, int nowait_onoff); </pre>
<p>
Configures the database handle to obtain a write lock on the
entire database when it is opened. This gives the handle
exclusive access to the database, because the write lock will block
all other threads of control for both read and write access.
</p>
<p>
Use this method to improve the throughput performance on your
database for the thread that is controlling this handle. When
configured with this method, operations on the database do not
acquire page locks as they perform read and/or write operations.
Also, the exclusive lock means that operations performed on the
database handle will never be blocked waiting for lock due to
another thread's activities. The application will also be immune to
deadlocks.
</p>
<p>
On the other hand, use of this method means that you can only
have a single thread accessing the database until the handle is
closed. For some applications, the loss of multiple threads
concurrently operating on the database will result in
performance degradation.
</p>
<p>
Also, use of this method means that you can only have one
transaction active for the handle at a time.
</p>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<h3 class="title">Note</h3>
<p>
This method is incompatible with the
<a class="link" href="dbopen.html#open_DB_THREAD">DB_THREAD</a> configuration
flag.
</p>
</div>
<p>
The <code class="methodname">DB->set_lk_exclusive()</code> method may
not be called after the
<a class="xref" href="dbopen.html" title="DB->open()">DB->open()</a> method is called.
</p>
<p>
The <code class="methodname">DB->set_lk_exclusive()</code> <span>
<span>
method returns a non-zero error value on failure and 0 on success.
</span>
</span>
</p>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="lk_exclusive_rep_notes"></a>Replication Notes</h3>
</div>
</div>
</div>
<p>
Replication applications that use exclusive database handles
need to be written with caution. This is because replication
clients cannot process updates on an exclusive database until
all local handles on the database are closed. Also, attempting
to open an exclusive database handle on a currently operating
client will result in the open call failing with the error
<code class="literal">EINVAL</code>.
</p>
<p>
Also, opening an exclusive database handle on a replication
master will result in all clients being locked out of the
database. On clients, existing handles on the exclusive
database will return the error
<code class="literal">DB_REP_DEAD_HANDLE</code> when accessed, and must
be closed. New handles opened on the exclusive database will
block until the master closes its exclusive database handle.
</p>
</div>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="idm5565920"></a>Parameters</h3>
</div>
</div>
</div>
<div class="sect3" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h4 class="title"><a id="idm4733328"></a>nowait_onoff</h4>
</div>
</div>
</div>
<p>
If set to <code class="literal">0</code>, this method will block
until it can obtain the exclusive lock on the database. If
set to some value other than <code class="literal">0</code>,
<code class="literal">DB_LOCK_NOTGRANTED</code> is returned when the
handle is opened if the exclusive database lock cannot be
immediately obtained.
</p>
</div>
</div>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="idm4350632"></a>Errors</h3>
</div>
</div>
</div>
<p>
The <code class="methodname">DB->set_lk_exclusive()</code> <span>
<span>
method may fail and return one of the following non-zero errors:
</span>
</span>
</p>
<div class="sect3" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h4 class="title"><a id="idm5844848"></a>EINVAL</h4>
</div>
</div>
</div>
<p>
If the method was called after
<a class="xref" href="dbopen.html" title="DB->open()">DB->open()</a>
was called; the method was called on a currently operating
replication client; or if an invalid flag value or
parameter was specified.
</p>
</div>
</div>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="idm6606456"></a>Class</h3>
</div>
</div>
</div>
<p>
<a class="link" href="db.html" title="Chapter 2. The DB Handle">DB</a>
</p>
</div>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="idm5877936"></a>See Also</h3>
</div>
</div>
</div>
<p>
<a class="xref" href="db.html#dblist" title="Database and Related Methods">Database and Related Methods</a>
</p>
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