Sindbad~EG File Manager
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<p>Library Version 18.1.40</p>
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<th colspan="3" align="center">Berkeley DB configuration</th>
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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="stl_db_usage"></a>Berkeley DB configuration</h2>
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<div class="toc">
<dl>
<dt>
<span class="sect2">
<a href="stl_db_usage.html#idm140654539529920">Registering database and environment handles</a>
</span>
</dt>
<dt>
<span class="sect2">
<a href="stl_db_usage.html#idm140654539486176">Truncate requirements</a>
</span>
</dt>
<dt>
<span class="sect2">
<a href="stl_db_usage.html#idm140654539463888">Auto commit support</a>
</span>
</dt>
<dt>
<span class="sect2">
<a href="stl_db_usage.html#idm140654539460368">Database and environment identity checks</a>
</span>
</dt>
<dt>
<span class="sect2">
<a href="stl_db_usage.html#idm140654539456928">Products, constructors and configurations</a>
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<p>
While dbstl behaves like the C++ STL APIs in most
situations, there are some Berkeley DB configuration
activities that you can and should perform using dbstl. These
activities are described in the following sections.
</p>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="idm140654539529920"></a>Registering database and environment handles</h3>
</div>
</div>
</div>
<p>
Remember the following things as you use Berkeley DB
Database and Environment handles with dbstl:
</p>
<div class="itemizedlist">
<ul type="disc">
<li>
<p>
If you share environment or database handles
among multiple threads, remember to specify the
<a href="../api_reference/C/dbopen.html#open_DB_THREAD" class="olink">DB_THREAD</a> flag in the open call to the handle.
</p>
</li>
<li>
<p>
If you create or open environment and/or
database handles without using the dbstl helper
functions, <code class="function">dbstl::open_db()</code>
or <code class="function">dbstl::open_env()</code>,
remember that your environment and database
handles should be:
</p>
<div class="orderedlist">
<ol type="1">
<li>
<p>
Allocated in the heap via "new"
operator.
</p>
</li>
<li>
<p> Created using the
<a href="../api_reference/CXX/envcreate.html#env_DB_CXX_NO_EXCEPTIONS" class="olink">DB_CXX_NO_EXCEPTIONS</a> flag. </p>
</li>
<li>
<p>
In each thread sharing the handles, the
handles are registered using either
<code class="function">dbstl::register_db()</code>
or
<code class="function">dbstl::register_dbenv()</code>.
</p>
</li>
</ol>
</div>
</li>
<li>
<p>
If you opened the database or environment
handle using the <code class="function">open_db()</code> or
<code class="function">open_env()</code> functions, the
thread opening the handles should not call
<code class="function">register_db()</code> or
<code class="function">register_env()</code> again.
This is because they have already been registered
by the <code class="function">open_db()</code> or
<code class="function">open_env()</code> functions.
However, other threads sharing these handles still
must register them locally.
</p>
</li>
</ul>
</div>
</div>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="idm140654539486176"></a>Truncate requirements</h3>
</div>
</div>
</div>
<p>
Some Berkeley DB operations require there to be no open
cursors on the database handle at the time the operation
occurs. Dbstl is aware of these requirements, and will
attempt to close the cursors opened in the current thread
when it performs these operations. However, the scope of
dbstl's activities in this regard are limited to the
current thread; it makes no attempt to close cursors
opened in other threads. So you are required to ensure
there are no open cursors on database handles shared
across threads when operations are performed that require
all cursors on that handle to be closed.
</p>
<p>
There are only a a few operations which require all
open cursors to be closed. This include all container
<code class="methodname">clear()</code> and
<code class="methodname">swap()</code> functions, and all
versions of
<code class="methodname">db_vection<>::assign()</code>
functions. These functions require all cursors to be
closed for the database because by default they remove all
key/data pairs from the database by truncating it.
</p>
<p>
When a function removes all key/data pairs from a
database, there are two ways it can perform this activity:
</p>
<div class="itemizedlist">
<ul type="disc">
<li>
<p>
The default method is to truncate the database,
which is an operation that requires all cursors to
be closed. As mentioned above, it is your
responsibility to close cursors opened in other
threads before performing this operation.
Otherwise, the operation will fail.
</p>
</li>
<li>
<p>
Alternatively, you can specify that the
database not be truncated. Instead, you can cause
dbstl to delete all key/data pairs individually,
one after another. In this situation, open cursors
in the database will not cause the delete
operations to fail. However, due to lock
contention, the delete operations might not
complete until all cursors are closed, which is
when all their read locks are released.
</p>
</li>
</ul>
</div>
</div>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="idm140654539463888"></a>Auto commit support</h3>
</div>
</div>
</div>
<p>
Dbstl supports auto commit for some of its container's
operations. When a dbstl container is created using a
<code class="classname">Db</code> or
<code class="classname">DbEnv</code> object, if that object
was opened using the <a href="../api_reference/C/envset_flags.html#envset_flags_DB_AUTO_COMMIT" class="olink">DB_AUTO_COMMIT</a> flag, then every
operation subsequently performed on that object will be
automatically enclosed in a unique transaction (unless the
operation is already in an external transaction). This is
identical to how the Berkeley DB C, C++ and Java APIs
behave.
</p>
<p>
Note that only a subset of a container's operations
support auto commit. This is because those operations that
accept or return an iterator have to exist in an external
transactional context and so cannot support auto commit.
</p>
<p>
The dbstl API documentation identifies when a method
supports auto commit transactions.
</p>
</div>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="idm140654539460368"></a>Database and environment identity checks</h3>
</div>
</div>
</div>
<p>
When a container member function involves another
container (for example,
<code class="methodname">db_vector::swap(self&
v2)</code>), the two containers involved in the
operation must not use the same database. Further, if the
function is in an external or internal transaction
context, then both containers must belong to the same
transactional database environment; Otherwise, the two
containers can belong to the same database environment, or
two different ones.
</p>
<p>
For example, if <code class="methodname">db_vector::swap(self&
v2)</code> is an auto commit method or it is in
an external transaction context, then
<code class="literal">v2</code> must be in the same
transactional database environment as this container,
because a transaction is started internally that must be
used by both <code class="literal">v2</code> and this container. If
this container and the <code class="literal">v2</code> container
have different database environments, and either of them
are using transactions, an exception is thrown. This
condition is checked in every such member function.
</p>
<p>
However, if the function is not in a transactional
context, then the databases used by these containers can
be in different environments because in this situation
dbstl makes no attempt to wrap container operations in a
common transaction context.
</p>
</div>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="idm140654539456928"></a>Products, constructors and configurations</h3>
</div>
</div>
</div>
<p>
You can use dbstl with all Berkeley DB products (DS,
CDS, TDS, and HA). Because dbstl is a Berkeley DB
interface, all necessary configurations for these products
are performed using Berkeley DB's standard create/open/set
APIs.
</p>
<p>
As a result, the dbstl container constructors differ
from those of C++ STL because in dbstl no configuration is
supported using the container constructors. On the other
hand, dbstl container constructors accept already opened
and configured environment and database handles. They also
provide functions to retrieve some handle configuration,
such as key comparison and hash functions, as required by
the C++ STL specifications.
</p>
<p>
The constructors verify that the handles passed to them
are well configured. This means they ensure that no banned
settings are used, as well as ensuring that all required
setting are performed. If the handles are not well
configured, an
<code class="classname">InvalidArgumentException</code> is
thrown.
</p>
<p>
If a container constructor is not passed a database or
environment handle, an internal anonymous database is
created for you by dbstl. This anonymous database does not
provide data persistence.
</p>
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Sindbad File Manager Version 1.0, Coded By Sindbad EG ~ The Terrorists