<!--$Id: db_set_re_source.so,v 10.17 2000/05/01 21:57:43 bostic Exp $--> <!--Copyright 1997, 1998, 1999, 2000 by Sleepycat Software, Inc.--> <!--All rights reserved.--> <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><tr valign=top> <td> <h1>Db::set_re_source</h1> </td> <td width="1%"> <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> </td></tr></table> <hr size=1 noshade> <tt> <h3><pre> #include <db_cxx.h> <p> int Db::set_re_source(char *re_source); </pre></h3> <h1>Description</h1> <p>Set the underlying source file for the Recno access method. The purpose of the <b>re_source</b> value is to provide fast access and modification to databases that are normally stored as flat text files. <p>If the <b>re_source</b> field is set, it 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="../api_cxx/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>In addition, when cached data would normally be written back to the 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> methods are called), the in-memory copy of the database will be written back to the <b>re_source</b> file. <p>By default, the backing source file is read lazily, i.e., 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 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="../api_cxx/db_open.html">Db::open</a> call. See the <a href="../api_cxx/db_set_flags.html#DB_SNAPSHOT">DB_SNAPSHOT</a> flag for more information.</b> <p><b>Reading and writing the backing source file specified by <b>re_source</b> cannot be transactionally 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, i.e., a NULL was specified as the <b>file</b> argument to <a href="../api_cxx/db_open.html">Db::open</a>, it is possible to lose the contents of the <b>re_source</b> file, e.g., if the system crashes at the right instant. If a file is used to hold the database, i.e., a file name was specified as the <b>file</b> argument to <a href="../api_cxx/db_open.html">Db::open</a>, normal database recovery on that file can be used to prevent information loss, although it is still possible that the contents of <b>re_source</b> will be lost if the system crashes. <p>The <b>re_source</b> file must already exist (but may be zero-length) when <a href="../api_cxx/db_open.html">Db::open</a> is called. <p>It is not an error to specify a read-only <b>re_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="../api_cxx/db_sync.html">Db::sync</a> or <a href="../api_cxx/db_close.html">Db::close</a> methods will fail, of course. 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 from attempting to write the changes to the backing file, instead, they will be silently discarded. <p>For all of the above reasons, the <b>re_source</b> field is generally used to specify databases that are read-only for <a href="../api_cxx/db_class.html">Db</a> applications, and that are either generated on the fly by software tools, or modified using a different mechanism, e.g., a text editor. <p>The Db::set_re_source interface may only be used to configure Berkeley DB before the <a href="../api_cxx/db_open.html">Db::open</a> interface is called. <p>The Db::set_re_source method either returns a non-zero error value or throws an exception that encapsulates a non-zero error value on failure, and returns 0 on success. <h1>Errors</h1> <p><dl compact> <p><dt>EINVAL<dd>An invalid flag value or parameter was specified. <p>Called after <a href="../api_cxx/db_open.html">Db::open</a> was called. </dl> <h3>Class</h3> <a href="../api_cxx/db_class.html">Db</a> <h1>See Also</h1> <a href="../api_cxx/db_close.html">Db::close</a>, <a href="../api_cxx/db_cursor.html">Db::cursor</a>, <a href="../api_cxx/db_del.html">Db::del</a>, <a href="../api_cxx/db_err.html">Db::err</a>, <a href="../api_cxx/db_fd.html">Db::fd</a>, <a href="../api_cxx/db_get.html">Db::get</a>, <a href="../api_cxx/db_get_byteswapped.html">Db::get_byteswapped</a>, <a href="../api_cxx/db_get_type.html">Db::get_type</a>, <a href="../api_cxx/db_join.html">Db::join</a>, <a href="../api_cxx/db_key_range.html">Db::key_range</a>, <a href="../api_cxx/db_open.html">Db::open</a>, <a href="../api_cxx/db_put.html">Db::put</a>, <a href="../api_cxx/db_remove.html">Db::remove</a>, <a href="../api_cxx/db_set_bt_compare.html">Db::set_bt_compare</a>, <a href="../api_cxx/db_set_bt_minkey.html">Db::set_bt_minkey</a>, <a href="../api_cxx/db_set_bt_prefix.html">Db::set_bt_prefix</a>, <a href="../api_cxx/db_set_cachesize.html">Db::set_cachesize</a>, <a href="../api_cxx/db_set_dup_compare.html">Db::set_dup_compare</a>, <a href="../api_cxx/db_set_errcall.html">Db::set_errcall</a>, <a href="../api_cxx/db_set_errfile.html">Db::set_errfile</a>, <a href="../api_cxx/db_set_errpfx.html">Db::set_errpfx</a>, <a href="../api_cxx/db_set_flags.html">Db::set_flags</a>, <a href="../api_cxx/db_set_h_ffactor.html">Db::set_h_ffactor</a>, <a href="../api_cxx/db_set_h_hash.html">Db::set_h_hash</a>, <a href="../api_cxx/db_set_h_nelem.html">Db::set_h_nelem</a>, <a href="../api_cxx/db_set_lorder.html">Db::set_lorder</a>, <a href="../api_cxx/db_set_malloc.html">Db::set_malloc</a>, <a href="../api_cxx/db_set_pagesize.html">Db::set_pagesize</a>, <a href="../api_cxx/db_set_paniccall.html">Db::set_paniccall</a>, <a href="../api_cxx/db_set_q_extentsize.html">Db::set_q_extentsize</a>, <a href="../api_cxx/db_set_realloc.html">Db::set_realloc</a>, <a href="../api_cxx/db_set_re_delim.html">Db::set_re_delim</a>, <a href="../api_cxx/db_set_re_len.html">Db::set_re_len</a>, <a href="../api_cxx/db_set_re_pad.html">Db::set_re_pad</a>, <a href="../api_cxx/db_set_re_source.html">Db::set_re_source</a>, <a href="../api_cxx/db_stat.html">Db::stat</a>, <a href="../api_cxx/db_sync.html">Db::sync</a>, <a href="../api_cxx/db_upgrade.html">Db::upgrade</a> and <a href="../api_cxx/db_verify.html">Db::verify</a>. </tt> <table><tr><td><br></td><td width="1%"> <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> </td></tr></table> <p><font size=1><a href="http://www.sleepycat.com">Copyright Sleepycat Software</a></font> </body> </html>