Import BSDDB 4.7.25 (as of svn r89086)
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Zachary Ware
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docs/api_cxx/db_set_re_source.html
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docs/api_cxx/db_set_re_source.html
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<!--$Id: db_set_re_source.html 63573 2008-05-23 21:43:21Z trent.nelson $-->
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<!--Copyright (c) 1997,2008 Oracle. All rights reserved.-->
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<!--See the file LICENSE for redistribution information.-->
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<html>
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<head>
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<title>Berkeley DB: Db::set_re_source</title>
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<meta name="description" content="Berkeley DB: An embedded database programmatic toolkit.">
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<meta name="keywords" content="embedded,database,programmatic,toolkit,btree,hash,hashing,transaction,transactions,locking,logging,access method,access methods,Java,C,C++">
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</head>
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<body bgcolor=white>
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<table width="100%"><tr valign=top>
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<td>
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<b>Db::set_re_source</b>
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</td>
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<td align=right>
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<a href="../api_cxx/api_core.html"><img src="../images/api.gif" alt="API"></a>
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<a href="../ref/toc.html"><img src="../images/ref.gif" alt="Ref"></a></td>
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</tr></table>
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<hr size=1 noshade>
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<tt>
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<b><pre>
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#include <db_cxx.h>
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<p>
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int
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Db::set_re_source(char *source);
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<p>
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int
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Db::get_re_source(const char **sourcep);
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</pre></b>
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<hr size=1 noshade>
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<b>Description: Db::set_re_source</b>
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<p>Set the underlying source file for the Recno access method. The purpose
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of the <b>source</b> value is to provide fast access and modification
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to databases that are normally stored as flat text files.</p>
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<p>The <b>source</b> parameter specifies an underlying flat text database
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file that is read to initialize a transient record number index. In
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the case of variable length records, the records are separated, as
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specified by <a href="../api_cxx/db_set_re_delim.html">Db::set_re_delim</a>. For example, standard UNIX byte
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stream files can be interpreted as a sequence of variable length records
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separated by <newline> characters.</p>
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<p>In addition, when cached data would normally be written back to the
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underlying database file (for example, the <a href="../api_cxx/db_close.html">Db::close</a> or
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<a href="../api_cxx/db_sync.html">Db::sync</a> methods are called), the in-memory copy of the database
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will be written back to the <b>source</b> file.</p>
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<p>By default, the backing source file is read lazily; that is, records
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are not read from the file until they are requested by the application.
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<b>If multiple processes (not threads) are accessing a Recno database
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concurrently, and are either inserting or deleting records, the backing
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source file must be read in its entirety before more than a single
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process accesses the database, and only that process should specify the
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backing source file as part of the <a href="../api_cxx/db_open.html">Db::open</a> call. See the
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<a href="../api_cxx/db_set_flags.html#DB_SNAPSHOT">DB_SNAPSHOT</a> flag for more information.</b></p>
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<p><b>Reading and writing the backing source file specified by <b>source</b>
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cannot be transaction-protected because it involves filesystem
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operations that are not part of the Db transaction methodology.</b> For
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this reason, if a temporary database is used to hold the records, it is
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possible to lose the contents of the <b>source</b> file, for
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example, if the system crashes at the right instant. If a file is used
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to hold the database, normal database recovery on that file can be used
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to prevent information loss, although it is still possible that the
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contents of <b>source</b> will be lost if the system crashes.</p>
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<p>The <b>source</b> file must already exist (but may be zero-length) when
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<a href="../api_cxx/db_open.html">Db::open</a> is called.</p>
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<p>It is not an error to specify a read-only <b>source</b> file when
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creating a database, nor is it an error to modify the resulting database.
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However, any attempt to write the changes to the backing source file using
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either the <a href="../api_cxx/db_sync.html">Db::sync</a> or <a href="../api_cxx/db_close.html">Db::close</a> methods will fail, of course.
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Specify the <a href="../api_cxx/db_close.html#DB_NOSYNC">DB_NOSYNC</a> flag to the <a href="../api_cxx/db_close.html">Db::close</a> method to stop it
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from attempting to write the changes to the backing file; instead, they
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will be silently discarded.</p>
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<p>For all of the previous reasons, the <b>source</b> field is generally
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used to specify databases that are read-only for Berkeley DB applications;
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and that are either generated on the fly by software tools or modified
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using a different mechanism -- for example, a text editor.</p>
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<p>The Db::set_re_source method configures operations performed using the specified
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<a href="../api_cxx/db_class.html">Db</a> handle, not all operations performed on the underlying
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database.</p>
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<p>The Db::set_re_source method may not be called after the <a href="../api_cxx/db_open.html">Db::open</a> method is called.
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If the database already exists when
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<a href="../api_cxx/db_open.html">Db::open</a> is called, the information specified to Db::set_re_source must
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be the same as that historically used to create the database or
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corruption can occur.</p>
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<p>The Db::set_re_source method
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either returns a non-zero error value
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or throws an exception that encapsulates a non-zero error value on
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failure, and returns 0 on success.
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</p>
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<b>Parameters</b> <br>
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<b>source</b><ul compact><li>The backing flat text database file for a Recno database.</ul>
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<p>When using a Unicode build on Windows (the default), the <b>source</b>
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argument will be interpreted as a UTF-8 string, which is equivalent to
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ASCII for Latin characters.</p>
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<br>
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<br><b>Errors</b>
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<p>The Db::set_re_source method
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may fail and throw
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<a href="../api_cxx/except_class.html">DbException</a>,
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encapsulating one of the following non-zero errors, or return one of
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the following non-zero errors:</p>
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<br>
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<b>EINVAL</b><ul compact><li>If the method was called after <a href="../api_cxx/db_open.html">Db::open</a> was called; or if an
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invalid flag value or parameter was specified.</ul>
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<br>
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<hr size=1 noshade>
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<b>Description: Db::get_re_source</b>
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<p>The Db::get_re_source method returns the source file.</p>
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<p>The Db::get_re_source method may be called at any time during the life of the
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application.</p>
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<hr size=1 noshade>
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<br><b>Class</b>
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<a href="../api_cxx/db_class.html">Db</a>
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<br><b>See Also</b>
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<a href="../api_cxx/db_list.html">Databases and Related Methods</a>
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</tt>
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<table width="100%"><tr><td><br></td><td align=right>
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<a href="../api_cxx/api_core.html"><img src="../images/api.gif" alt="API"></a><a href="../ref/toc.html"><img src="../images/ref.gif" alt="Ref"></a>
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</td></tr></table>
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<p><font size=1>Copyright (c) 1996,2008 Oracle. All rights reserved.</font>
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</body>
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</html>
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