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106 lines
5 KiB
HTML
<!--$Id: db_set_bt_prefix.so,v 10.25 2000/09/08 21:35:26 bostic Exp $-->
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<!--Copyright 1997, 1998, 1999, 2000 by Sleepycat Software, Inc.-->
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<!--All rights reserved.-->
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<html>
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<head>
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<title>Berkeley DB: Db.set_bt_prefix</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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</head>
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<body bgcolor=white>
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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_bt_prefix</h1>
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</td>
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<td width="1%">
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<a href="../api_java/java_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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import com.sleepycat.db.*;
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<p>
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public interface DbBtreePrefix
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{
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public abstract int bt_prefix(Db db, Dbt dbt1, Dbt dbt2);
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}
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public class Db
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{
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public void set_bt_prefix(DbBtreePrefix bt_prefix)
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throws DbException;
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...
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}
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</pre></h3>
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<h1>Description</h1>
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<p>Set the Btree prefix function. The prefix function must return the
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number of bytes of the second key argument that would be required by
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the Btree key comparison function to determine the second key argument's
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ordering relationship with respect to the first key argument. If the
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two keys are equal, the key length should be returned. The prefix
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function must correctly handle any key values used by the application
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(possibly including zero-length keys). The <b>data</b> and
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<b>size</b> fields of the <a href="../api_java/dbt_class.html">Dbt</a> are the only fields that may be
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used for the purposes of this determination.
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<p>The prefix function is used to determine the amount by which keys stored
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on the Btree internal pages can be safely truncated without losing their
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uniqueness. See the <a href="../ref/am_conf/bt_prefix.html">Btree
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prefix comparison</a> section of the Reference Guide for more details about
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how this works. The usefulness of this is data dependent, but in some
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data sets can produce significantly reduced tree sizes and search times.
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<p>If no prefix function or key comparison function is specified by the
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application, a default lexical comparison function is used as the prefix
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function. If no prefix function is specified and a key comparison
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function is specified, no prefix function is used. It is an error to
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specify a prefix function without also specifying a key comparison
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function.
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<p>The Db.set_bt_prefix interface may only be used to configure Berkeley DB before
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the <a href="../api_java/db_open.html">Db.open</a> interface is called.
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<p>The Db.set_bt_prefix method throws an exception that encapsulates a non-zero error value on
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failure.
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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_java/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_java/db_class.html">Db</a>
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<h1>See Also</h1>
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<a href="../api_java/db_close.html">Db.close</a>,
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<a href="../api_java/db_cursor.html">Db.cursor</a>,
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<a href="../api_java/db_del.html">Db.del</a>,
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<a href="../api_java/db_fd.html">Db.fd</a>,
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<a href="../api_java/db_get.html">Db.get</a>,
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<a href="../api_java/db_get_byteswapped.html">Db.get_byteswapped</a>,
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<a href="../api_java/db_get_type.html">Db.get_type</a>,
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<a href="../api_java/db_join.html">Db.join</a>,
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<a href="../api_java/db_key_range.html">Db.key_range</a>,
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<a href="../api_java/db_open.html">Db.open</a>,
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<a href="../api_java/db_put.html">Db.put</a>,
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<a href="../api_java/db_remove.html">Db.remove</a>,
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<a href="../api_java/db_set_bt_minkey.html">Db.set_bt_minkey</a>,
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<a href="../api_java/db_set_cachesize.html">Db.set_cachesize</a>,
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<a href="../api_java/db_set_errcall.html">Db.set_errcall</a>,
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<a href="../api_java/db_set_errpfx.html">Db.set_errpfx</a>,
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<a href="../api_java/db_set_flags.html">Db.set_flags</a>,
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<a href="../api_java/db_set_h_ffactor.html">Db.set_h_ffactor</a>,
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<a href="../api_java/db_set_h_nelem.html">Db.set_h_nelem</a>,
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<a href="../api_java/db_set_lorder.html">Db.set_lorder</a>,
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<a href="../api_java/db_set_pagesize.html">Db.set_pagesize</a>,
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<a href="../api_java/db_set_q_extentsize.html">Db.set_q_extentsize</a>,
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<a href="../api_java/db_set_re_delim.html">Db.set_re_delim</a>,
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<a href="../api_java/db_set_re_len.html">Db.set_re_len</a>,
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<a href="../api_java/db_set_re_pad.html">Db.set_re_pad</a>,
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<a href="../api_java/db_set_re_source.html">Db.set_re_source</a>,
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<a href="../api_java/db_stat.html">Db.stat</a>,
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<a href="../api_java/db_sync.html">Db.sync</a>,
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<a href="../api_java/db_upgrade.html">Db.upgrade</a>
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and
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<a href="../api_java/db_verify.html">Db.verify</a>.
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</tt>
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<table><tr><td><br></td><td width="1%">
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<a href="../api_java/java_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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<p><font size=1><a href="http://www.sleepycat.com">Copyright Sleepycat Software</a></font>
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