<!--$Id: intro.so,v 1.5 2006/11/13 18:05:03 bostic Exp $--> <!--Copyright (c) 1997,2008 Oracle. All rights reserved.--> <!--See the file LICENSE for redistribution information.--> <html> <head> <title>Berkeley DB Reference Guide: Introduction to sequences</title> <meta name="description" content="Berkeley DB: An embedded database programmatic toolkit."> <meta name="keywords" content="embedded,database,programmatic,toolkit,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><b><dl><dt>Berkeley DB Reference Guide:<dd>Sequences</dl></b></td> <td align=right><a href="../txn/limits.html"><img src="../../images/prev.gif" alt="Prev"></a><a href="../toc.html"><img src="../../images/ref.gif" alt="Ref"></a><a href="../rpc/intro.html"><img src="../../images/next.gif" alt="Next"></a> </td></tr></table> <p align=center><b>Introduction to sequences</b></p> <p>Sequences provide an arbitrary number of persistent objects that return an increasing or decreasing sequence of integers. Opening a sequence handle associates it with a record in a database. The handle can maintain a cache of values from the database so that a database update is not needed as the application allocates a value.</p> <p>A sequence is stored as a record pair in a database. The database may be of any type, but may not have been configured to support duplicate data items. The sequence is referenced by the key used when the sequence is created, therefore the key must be compatible with the underlying access method. If the database stores fixed-length records, the record size must be at least 64 bytes long.</p> <p>Since a sequence handle is opened using a database handle, the use of transactions with the sequence must follow how the database handle was opened. In other words, if the database handle was opened within a transaction, operations on the sequence handle must use transactions. Of course, if sequences are cached, not all operations will actually trigger a transaction.</p> <p>For the highest concurrency, caching should be used and the <a href="../../api_c/env_set_flags.html#DB_AUTO_COMMIT">DB_AUTO_COMMIT</a> and <a href="../../api_c/env_set_flags.html#DB_TXN_NOSYNC">DB_TXN_NOSYNC</a> flags should be specified to the <a href="../../api_c/seq_get.html">DB_SEQUENCE->get</a> method call. If the allocation of the sequence value must be part of a transaction, and rolled back if the transaction aborts, then no caching should be specified and the transaction handle must be passed to the <a href="../../api_c/seq_get.html">DB_SEQUENCE->get</a> method.</p> <!--$Id: m4.methods,v 1.7 2004/11/29 15:34:22 bostic Exp $--> <table border=1 align=center> <tr><th>Sequences and Related Methods</th><th>Description</th></tr> <!--DbSequence::--><tr><td><a href="../../api_c/seq_class.html">db_sequence_create</a></td><td>Create a sequence handle</td></tr> <!--DbSequence::close--><tr><td><a href="../../api_c/seq_close.html">DB_SEQUENCE->close</a></td><td>Close a sequence</td></tr> <!--DbSequence::get--><tr><td><a href="../../api_c/seq_get.html">DB_SEQUENCE->get</a></td><td>Get the next sequence element(s)</td></tr> <!--DbSequence::get_dbp--><tr><td><a href="../../api_c/seq_open.html">DB_SEQUENCE->get_dbp</a></td><td>Return a handle for the underlying sequence database</td></tr> <!--DbSequence::get_key--><tr><td><a href="../../api_c/seq_open.html">DB_SEQUENCE->get_key</a></td><td>Return the key for a sequence</td></tr> <!--DbSequence::initial_value--><tr><td><a href="../../api_c/seq_initial_value.html">DB_SEQUENCE->initial_value</a></td><td>Set the initial value of a sequence</td></tr> <!--DbSequence::open--><tr><td><a href="../../api_c/seq_open.html">DB_SEQUENCE->open</a></td><td>Open a sequence</td></tr> <!--DbSequence::remove--><tr><td><a href="../../api_c/seq_remove.html">DB_SEQUENCE->remove</a></td><td>Remove a sequence</td></tr> <!--DbSequence::stat--><tr><td><a href="../../api_c/seq_stat.html">DB_SEQUENCE->stat</a></td><td>Return sequence statistics</td></tr> <tr><th>Sequences Configuration</th><th><br></th></tr> <!--DbSequence::set_cachesize--><tr><td><a href="../../api_c/seq_set_cachesize.html">DB_SEQUENCE->set_cachesize</a></td><td>Set the cache size of a sequence</td></tr> <!--DbSequence::set_flags--><tr><td><a href="../../api_c/seq_set_flags.html">DB_SEQUENCE->set_flags</a></td><td>Set the flags for a sequence</td></tr> <!--DbSequence::set_range--><tr><td><a href="../../api_c/seq_set_range.html">DB_SEQUENCE->set_range</a></td><td>Set the range for a sequence</td></tr> </table> <table width="100%"><tr><td><br></td><td align=right><a href="../txn/limits.html"><img src="../../images/prev.gif" alt="Prev"></a><a href="../toc.html"><img src="../../images/ref.gif" alt="Ref"></a><a href="../rpc/intro.html"><img src="../../images/next.gif" alt="Next"></a> </td></tr></table> <p><font size=1>Copyright (c) 1996,2008 Oracle. 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