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Yasuhiro KIMURA
99 lines
4.7 KiB
HTML
99 lines
4.7 KiB
HTML
<?xml version="1.0" encoding="UTF-8" standalone="no"?>
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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<html xmlns="http://www.w3.org/1999/xhtml">
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
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<title>Chapter 22. Sequences</title>
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<link rel="stylesheet" href="gettingStarted.css" type="text/css" />
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<meta name="generator" content="DocBook XSL Stylesheets V1.73.2" />
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<link rel="start" href="index.html" title="Berkeley DB Programmer's Reference Guide" />
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<link rel="up" href="index.html" title="Berkeley DB Programmer's Reference Guide" />
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<link rel="prev" href="txn_limits.html" title="Transaction limits" />
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<link rel="next" href="tcl.html" title="Chapter 23. Berkeley DB Extensions: Tcl" />
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</head>
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<body>
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<div xmlns="" class="navheader">
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<div class="libver">
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<p>Library Version 18.1.32</p>
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</div>
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<table width="100%" summary="Navigation header">
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<tr>
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<th colspan="3" align="center">Chapter 22. Sequences </th>
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</tr>
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<tr>
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<td width="20%" align="left"><a accesskey="p" href="txn_limits.html">Prev</a> </td>
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<th width="60%" align="center"> </th>
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<td width="20%" align="right"> <a accesskey="n" href="tcl.html">Next</a></td>
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</tr>
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</table>
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<hr />
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</div>
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<div class="chapter" lang="en" xml:lang="en">
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<div class="titlepage">
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<div>
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<div>
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<h2 class="title"><a id="sequence"></a>Chapter 22. Sequences </h2>
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</div>
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</div>
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</div>
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<p>
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Sequences provide an arbitrary number of persistent objects
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that return an increasing or decreasing sequence of integers.
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Opening a sequence handle associates it with a record in a
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database. The handle can maintain a cache of values from the
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database so that a database update is not needed as the
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application allocates a value.
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</p>
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<p>
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A sequence is stored as a record pair in a database. The
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database may be of any type, but may not have been configured
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to support duplicate data items. The sequence is referenced by
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the key used when the sequence is created, therefore the key
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must be compatible with the underlying access method. If the
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database stores fixed-length records, the record size must be
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at least 64 bytes long.
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</p>
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<p>
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Since a sequence handle is opened using a database handle,
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the use of transactions with the sequence must follow how the
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database handle was opened. In other words, if the database
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handle was opened within a transaction, operations on the
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sequence handle must use transactions. Of course, if sequences
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are cached, not all operations will actually trigger a
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transaction.
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</p>
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<p>
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For the highest concurrency, caching should be used and the
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<a href="../api_reference/C/envset_flags.html#envset_flags_DB_AUTO_COMMIT" class="olink">DB_AUTO_COMMIT</a> and <a href="../api_reference/C/envset_flags.html#envset_flags_DB_TXN_NOSYNC" class="olink">DB_TXN_NOSYNC</a> flags should be specified
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to the <a href="../api_reference/C/seqget.html" class="olink">DB_SEQUENCE->get()</a> method call. If the allocation of the sequence
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value must be part of a transaction, and rolled back if the
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transaction aborts, then no caching should be specified and
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the transaction handle must be passed to the <a href="../api_reference/C/seqget.html" class="olink">DB_SEQUENCE->get()</a>
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method.
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</p>
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<p>
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For more information on the operations supported by the
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sequence handle, see the <a href="../api_reference/C/seq.html#seqlist" class="olink">Sequences and Related Methods</a>
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section in the <em class="citetitle">Berkeley DB C API Reference Guide.</em>
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</p>
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</div>
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<div class="navfooter">
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<hr />
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<table width="100%" summary="Navigation footer">
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<tr>
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<td width="40%" align="left"><a accesskey="p" href="txn_limits.html">Prev</a> </td>
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<td width="20%" align="center"> </td>
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<td width="40%" align="right"> <a accesskey="n" href="tcl.html">Next</a></td>
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</tr>
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<tr>
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<td width="40%" align="left" valign="top">Transaction limits </td>
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<td width="20%" align="center">
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<a accesskey="h" href="index.html">Home</a>
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</td>
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<td width="40%" align="right" valign="top"> Chapter 23. Berkeley DB Extensions: Tcl </td>
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</tr>
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</table>
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</div>
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</body>
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</html>
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