<!--$Id: db_set_re_source.so,v 10.38 2003/11/08 19:17:22 bostic Exp $--> <!--Copyright 1997-2003 by Sleepycat Software, Inc.--> <!--All rights reserved.--> <!--See the file LICENSE for redistribution information.--> <html> <head> <title>Berkeley DB: DB->set_re_source</title> <meta name="description" content="Berkeley DB: An embedded database programmatic toolkit."> <meta name="keywords" content="embedded,database,programmatic,toolkit,b+tree,btree,hash,hashing,transaction,transactions,locking,logging,access method,access methods,Java,C,C++"> </head> <body bgcolor=white> <a name="2"><!--meow--></a> <table width="100%"><tr valign=top> <td> <h3>DB->set_re_source</h3> </td> <td align=right> <a href="../../db42-devel-4.2.52/api_c/api_index.html"><img src="../../db42-4.2.52/images/api.gif" alt="API"></a> <a href="../../db42-devel-4.2.52/ref/toc.html"><img src="../../db42-4.2.52/images/ref.gif" alt="Ref"></a> </td></tr></table> <hr size=1 noshade> <tt> <h3><pre> #include <db.h> <p> int DB->set_re_source(DB *db, char *source); <p> int DB->get_re_source(DB *db, const char **sourcep); </pre></h3> <hr size=1 noshade> <h3>Description: DB->set_re_source</h3> <a name="3"><!--meow--></a> <p>Set the underlying source file for the Recno access method. The purpose of the <b>source</b> value is to provide fast access and modification to databases that are normally stored as flat text files.</p> <p>The <b>source</b> 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="../../db42-devel-4.2.52/api_c/db_set_re_delim.html">DB->set_re_delim</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, the <a href="../../db42-devel-4.2.52/api_c/db_close.html">DB->close</a> or <a href="../../db42-devel-4.2.52/api_c/db_sync.html">DB->sync</a> methods are called), the in-memory copy of the database will be written back to the <b>source</b> 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. <b>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="../../db42-devel-4.2.52/api_c/db_open.html">DB->open</a> call. See the <a href="../../db42-devel-4.2.52/api_c/db_set_flags.html#DB_SNAPSHOT">DB_SNAPSHOT</a> flag for more information.</b></p> <p><b>Reading and writing the backing source file specified by <b>source</b> cannot be transaction-protected because it involves filesystem operations that are not part of the Db transaction methodology.</b> For this reason, if a temporary database is used to hold the records, it is possible to lose the contents of the <b>source</b> 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 <b>source</b> will be lost if the system crashes.</p> <p>The <b>source</b> file must already exist (but may be zero-length) when <a href="../../db42-devel-4.2.52/api_c/db_open.html">DB->open</a> is called.</p> <p>It is not an error to specify a read-only <b>source</b> 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="../../db42-devel-4.2.52/api_c/db_sync.html">DB->sync</a> or <a href="../../db42-devel-4.2.52/api_c/db_close.html">DB->close</a> methods will fail, of course. Specify the <a href="../../db42-devel-4.2.52/api_c/db_close.html#DB_NOSYNC">DB_NOSYNC</a> flag to the <a href="../../db42-devel-4.2.52/api_c/db_close.html">DB->close</a> method 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 <b>source</b> field 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>The DB->set_re_source method configures operations performed using the specified <a href="../../db42-devel-4.2.52/api_c/db_class.html">DB</a> handle, not all operations performed on the underlying database.</p> <p>The DB->set_re_source method may not be called after the <a href="../../db42-devel-4.2.52/api_c/db_open.html">DB->open</a> method is called. If the database already exists when <a href="../../db42-devel-4.2.52/api_c/db_open.html">DB->open</a> is called, the information specified to DB->set_re_source must be the same as that historically used to create the database or corruption can occur.</p> <p>The DB->set_re_source method returns a non-zero error value on failure and 0 on success. </p> <h3>Parameters</h3> <p><dl compact> <p><dt><b>source</b><dd> The backing flat text database file for a Recno database. </dl> <h3>Errors</h3> <p>The DB->set_re_source method may fail and return one of the following non-zero errors:</p> <p><dl compact> <p><dt>EINVAL<dd>If the method was called after <a href="../../db42-devel-4.2.52/api_c/db_open.html">DB->open</a> was called; or if an invalid flag value or parameter was specified. </dl> <hr size=1 noshade> <h3>Description: DB->get_re_source</h3> <p>The DB->get_re_source method returns the source file.</p> <p>The DB->get_re_source method may be called at any time during the life of the application.</p> <hr size=1 noshade> <h3>Class</h3> <a href="../../db42-devel-4.2.52/api_c/db_class.html">DB</a> <h3>See Also</h3> <a href="../../db42-devel-4.2.52/api_c/db_list.html">Databases and Related Methods</a> </tt> <table width="100%"><tr><td><br></td><td align=right> <a href="../../db42-devel-4.2.52/api_c/api_index.html"><img src="../../db42-4.2.52/images/api.gif" alt="API"></a><a href="../../db42-devel-4.2.52/ref/toc.html"><img src="../../db42-4.2.52/images/ref.gif" alt="Ref"></a> </td></tr></table> <p><font size=1><a href="../../db42-devel-4.2.52/sleepycat/legal.html">Copyright (c) 1996-2003</a> <a href="http://www.sleepycat.com">Sleepycat Software, Inc.</a> - All rights reserved.</font> </body> </html>
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