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<!--$Id: db_set_re_source.so,v 10.17 2000/05/01 21:57:43 bostic Exp $-->
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<!--Copyright 1997, 1998, 1999, 2000 by Sleepycat Software, Inc.-->
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<html>
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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,b+tree,btree,hash,hashing,transaction,transactions,locking,logging,access method,access methods,java,C,C++">
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<a name="2"><!--meow--></a>
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<table><tr valign=top>
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<td>
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<h1>Db::set_re_source</h1>
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</td>
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<td width="1%">
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<a href="../api_cxx/cxx_index.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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<hr size=1 noshade>
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<tt>
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<h3><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 *re_source);
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</pre></h3>
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<h1>Description</h1>
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<p>Set the underlying source file for the Recno access method. The purpose
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of the <b>re_source</b> value is to provide fast access and modification
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to databases that are normally stored as flat text files.
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<p>If the <b>re_source</b> field is set, it specifies an underlying flat
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text database file that is read to initialize a transient record number
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index. In the case of variable length records, the records are separated
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as specified by <a href="../api_cxx/db_set_re_delim.html">Db::set_re_delim</a>. For example, standard UNIX
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byte stream files can be interpreted as a sequence of variable length
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records separated by <newline> characters.
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<p>In addition, when cached data would normally be written back to the
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underlying database file (e.g., the <a href="../api_cxx/db_close.html">Db::close</a> or <a href="../api_cxx/db_sync.html">Db::sync</a>
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methods are called), the in-memory copy of the database will be written
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back to the <b>re_source</b> file.
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<p>By default, the backing source file is read lazily, i.e., records are not
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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 either inserting or deleting records, the backing source
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file must be read in its entirety before more than a single process
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accesses the database, and only that process should specify the backing
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source file as part of the <a href="../api_cxx/db_open.html">Db::open</a> call. See the <a href="../api_cxx/db_set_flags.html#DB_SNAPSHOT">DB_SNAPSHOT</a>
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flag for more information.</b>
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<p><b>Reading and writing the backing source file specified by <b>re_source</b>
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cannot be transactionally protected because it involves filesystem
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operations that are not part of the Db transaction methodology.</b>
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For this reason, if a temporary database is used to hold the records,
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i.e., a NULL was specified as the <b>file</b> argument to <a href="../api_cxx/db_open.html">Db::open</a>,
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it is possible to lose the contents of the <b>re_source</b> file, e.g.,
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if the system crashes at the right instant.
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If a file is used to hold the database, i.e., a file name was specified
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as the <b>file</b> argument to <a href="../api_cxx/db_open.html">Db::open</a>, normal database
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recovery on that file can be used to prevent information loss,
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although it is still possible that the contents of <b>re_source</b>
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will be lost if the system crashes.
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<p>The <b>re_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.
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<p>It is not an error to specify a read-only <b>re_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.
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<p>For all of the above reasons, the <b>re_source</b> field is generally
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used to specify databases that are read-only for <a href="../api_cxx/db_class.html">Db</a> 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, e.g., a text editor.
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<p>The Db::set_re_source interface may only be used to configure Berkeley DB before
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the <a href="../api_cxx/db_open.html">Db::open</a> interface is called.
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<p>The Db::set_re_source method either returns a non-zero error value or throws an exception that
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encapsulates a non-zero error value on failure, and returns 0 on success.
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<h1>Errors</h1>
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<p><dl compact>
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<p><dt>EINVAL<dd>An invalid flag value or parameter was specified.
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<p>Called after <a href="../api_cxx/db_open.html">Db::open</a> was called.
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</dl>
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<h3>Class</h3>
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<a href="../api_cxx/db_class.html">Db</a>
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<h1>See Also</h1>
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<a href="../api_cxx/db_close.html">Db::close</a>,
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<a href="../api_cxx/db_cursor.html">Db::cursor</a>,
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<a href="../api_cxx/db_del.html">Db::del</a>,
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<a href="../api_cxx/db_err.html">Db::err</a>,
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<a href="../api_cxx/db_fd.html">Db::fd</a>,
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<a href="../api_cxx/db_get.html">Db::get</a>,
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<a href="../api_cxx/db_get_byteswapped.html">Db::get_byteswapped</a>,
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<a href="../api_cxx/db_get_type.html">Db::get_type</a>,
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<a href="../api_cxx/db_join.html">Db::join</a>,
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<a href="../api_cxx/db_key_range.html">Db::key_range</a>,
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<a href="../api_cxx/db_open.html">Db::open</a>,
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<a href="../api_cxx/db_put.html">Db::put</a>,
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<a href="../api_cxx/db_remove.html">Db::remove</a>,
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<a href="../api_cxx/db_set_bt_compare.html">Db::set_bt_compare</a>,
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<a href="../api_cxx/db_set_bt_minkey.html">Db::set_bt_minkey</a>,
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<a href="../api_cxx/db_set_bt_prefix.html">Db::set_bt_prefix</a>,
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<a href="../api_cxx/db_set_cachesize.html">Db::set_cachesize</a>,
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<a href="../api_cxx/db_set_dup_compare.html">Db::set_dup_compare</a>,
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<a href="../api_cxx/db_set_errcall.html">Db::set_errcall</a>,
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<a href="../api_cxx/db_set_errfile.html">Db::set_errfile</a>,
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<a href="../api_cxx/db_set_errpfx.html">Db::set_errpfx</a>,
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<a href="../api_cxx/db_set_flags.html">Db::set_flags</a>,
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<a href="../api_cxx/db_set_h_ffactor.html">Db::set_h_ffactor</a>,
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<a href="../api_cxx/db_set_h_hash.html">Db::set_h_hash</a>,
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<a href="../api_cxx/db_set_h_nelem.html">Db::set_h_nelem</a>,
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<a href="../api_cxx/db_set_lorder.html">Db::set_lorder</a>,
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<a href="../api_cxx/db_set_malloc.html">Db::set_malloc</a>,
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<a href="../api_cxx/db_set_pagesize.html">Db::set_pagesize</a>,
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<a href="../api_cxx/db_set_paniccall.html">Db::set_paniccall</a>,
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<a href="../api_cxx/db_set_q_extentsize.html">Db::set_q_extentsize</a>,
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<a href="../api_cxx/db_set_realloc.html">Db::set_realloc</a>,
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<a href="../api_cxx/db_set_re_delim.html">Db::set_re_delim</a>,
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<a href="../api_cxx/db_set_re_len.html">Db::set_re_len</a>,
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<a href="../api_cxx/db_set_re_pad.html">Db::set_re_pad</a>,
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<a href="../api_cxx/db_set_re_source.html">Db::set_re_source</a>,
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<a href="../api_cxx/db_stat.html">Db::stat</a>,
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<a href="../api_cxx/db_sync.html">Db::sync</a>,
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<a href="../api_cxx/db_upgrade.html">Db::upgrade</a>
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and
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<a href="../api_cxx/db_verify.html">Db::verify</a>.
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</tt>
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