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The underlying source file for the Recno access method.
</div><p />
<b>Namespace:</b>
<a href="N_BerkeleyDB.htm">BerkeleyDB</a><br />
<b>Assembly:</b>
<span sdata="assembly">libdb_dotnet53</span> (in libdb_dotnet53.dll) Version: 5.3.28.0<h1 class="heading"><span onclick="ExpandCollapse(syntaxToggle)" style="cursor:default;" onkeypress="ExpandCollapse_CheckKey(syntaxToggle, event)" tabindex="0"><img id="syntaxToggle" class="toggle" name="toggleSwitch" src="../icons/collapse_all.gif" />Syntax</span></h1><div id="syntaxSection" class="section" name="collapseableSection" style=""><div id="syntaxCodeBlocks" class="code"><span codeLanguage="CSharp"><table><tr><th>C#</th></tr><tr><td><pre xml:space="preserve"><span class="keyword">public</span> <a href="http://msdn2.microsoft.com/en-us/library/s1wwdcbf" target="_blank">string</a> <span class="identifier">BackingFile</span></pre></td></tr></table></span><span codeLanguage="VisualBasicDeclaration"><table><tr><th>Visual Basic (Declaration)</th></tr><tr><td><pre xml:space="preserve"><span class="keyword">Public</span> <span class="identifier">BackingFile</span> <span class="keyword">As</span> <a href="http://msdn2.microsoft.com/en-us/library/s1wwdcbf" target="_blank">String</a></pre></td></tr></table></span><span codeLanguage="ManagedCPlusPlus"><table><tr><th>Visual C++</th></tr><tr><td><pre xml:space="preserve"><span class="keyword">public</span>:
<a href="http://msdn2.microsoft.com/en-us/library/s1wwdcbf" target="_blank">String</a>^ <span class="identifier">BackingFile</span></pre></td></tr></table></span></div></div><h1 class="heading"><span onclick="ExpandCollapse(remarksToggle)" style="cursor:default;" onkeypress="ExpandCollapse_CheckKey(remarksToggle, event)" tabindex="0"><img id="remarksToggle" class="toggle" name="toggleSwitch" src="../icons/collapse_all.gif" />Remarks</span></h1><div id="remarksSection" class="section" name="collapseableSection" style="">
<p>
The purpose of the source file is to provide fast access and
modification to databases that are normally stored as flat text
files.
</p>
<p>
The source parameter specifies an underlying flat text database file
that is read to initialize a transient record number index. In the
case of variable length records, the records are separated, as
specified by <a href="P_BerkeleyDB_RecnoDatabaseConfig_Delimiter.htm">Delimiter</a>. For example, standard UNIX
byte stream files can be interpreted as a sequence of variable
length records separated by newline characters.
</p>
<p>
In addition, when cached data would normally be written back to the
underlying database file (for example,
<a href="M_BerkeleyDB_BaseDatabase_Close.htm">Close<span class="languageSpecificText"><span class="cs">()</span><span class="cpp">()</span><span class="nu">()</span></span></a> or
<a href="M_BerkeleyDB_BaseDatabase_Sync.htm">Sync<span class="languageSpecificText"><span class="cs">()</span><span class="cpp">()</span><span class="nu">()</span></span></a>), the in-memory copy of the
database will be written back to the source file.
</p>
<p>
By default, the backing source file is read lazily; that is, records
are not read from the file until they are requested by the
application. If multiple processes (not threads) are accessing a
Recno database concurrently, and are either inserting or deleting
records, the backing source file must be read in its entirety before
more than a single process accesses the database, and only that
process should specify the backing source file as part of the
<a href="M_BerkeleyDB_RecnoDatabase_Open.htm">Open(String, RecnoDatabaseConfig)</a> call. See <a href="F_BerkeleyDB_RecnoDatabaseConfig_Snapshot.htm">Snapshot</a>
for more information.
</p>
<p>
Reading and writing the backing source file specified by source
cannot be transaction-protected because it involves filesystem
operations that are not part of the Db transaction methodology. For
this reason, if a temporary database is used to hold the records, it
is possible to lose the contents of the source file, for example, if
the system crashes at the right instant. If a file is used to hold
the database, normal database recovery on that file can be used to
prevent information loss, although it is still possible that the
contents of source will be lost if the system crashes.
</p>
<p>
The source file must already exist (but may be zero-length) when
<a href="M_BerkeleyDB_RecnoDatabase_Open.htm">Open(String, RecnoDatabaseConfig)</a> is called.
</p>
<p>
It is not an error to specify a read-only source file when creating
a database, nor is it an error to modify the resulting database.
However, any attempt to write the changes to the backing source file
using either the <a href="M_BerkeleyDB_BaseDatabase_Sync.htm">Sync<span class="languageSpecificText"><span class="cs">()</span><span class="cpp">()</span><span class="nu">()</span></span></a> or
<a href="M_BerkeleyDB_BaseDatabase_Close.htm">Close<span class="languageSpecificText"><span class="cs">()</span><span class="cpp">()</span><span class="nu">()</span></span></a> methods will fail, of course.
Use <a href="M_BerkeleyDB_BaseDatabase_Close_1.htm">Close(Boolean)</a> to stop it from
attempting to write the changes to the backing file; instead, they
will be silently discarded.
</p>
<p>
For all of the previous reasons, the source file is generally used
to specify databases that are read-only for Berkeley DB
applications; and that are either generated on the fly by software
tools or modified using a different mechanism — for example, a text
editor.
</p>
<p>
If the database already exists, BackingFile must be the same as that
historically used to create the database or corruption can occur.
</p>
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