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diff --git a/bdb/docs/ref/am_conf/bt_prefix.html b/bdb/docs/ref/am_conf/bt_prefix.html deleted file mode 100644 index 621de75fa6b..00000000000 --- a/bdb/docs/ref/am_conf/bt_prefix.html +++ /dev/null @@ -1,66 +0,0 @@ -<!--$Id: bt_prefix.so,v 10.17 2000/07/04 18:28:27 bostic Exp $--> -<!--Copyright 1997, 1998, 1999, 2000 by Sleepycat Software, Inc.--> -<!--All rights reserved.--> -<html> -<head> -<title>Berkeley DB Reference Guide: Btree prefix comparison</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> -<table><tr valign=top> -<td><h3><dl><dt>Berkeley DB Reference Guide:<dd>Access Methods</dl></h3></td> -<td width="1%"><a href="../../ref/am_conf/bt_compare.html"><img src="../../images/prev.gif" alt="Prev"></a><a href="../../ref/toc.html"><img src="../../images/ref.gif" alt="Ref"></a><a href="../../ref/am_conf/bt_minkey.html"><img src="../../images/next.gif" alt="Next"></a> -</td></tr></table> -<p> -<h1 align=center>Btree prefix comparison</h1> -<p>The Berkeley DB Btree implementation maximizes the number of keys that can be -stored on an internal page by storing only as many bytes of each key as -are necessary to distinguish it from adjacent keys. The prefix comparison -routine is what determines this minimum number of bytes (i.e., the length -of the unique prefix), that must be stored. A prefix comparison function -for the Btree can be specified by calling <a href="../../api_c/db_set_bt_prefix.html">DB->set_bt_prefix</a>. -<p>The prefix comparison routine must be compatible with the overall -comparison function of the Btree, since what distinguishes any two keys -depends entirely on the function used to compare them. This means that -if a prefix comparison routine is specified by the application, a -compatible overall comparison routine must also have been specified. -<p>Prefix comparison routines are passed pointers to keys as arguments. The -keys are represented as <a href="../../api_c/dbt.html">DBT</a> structures. The prefix comparison -function must return the number of bytes of the second key argument that -are necessary to determine if it is greater than the first key argument. -If the keys are equal, the length of the second key should be returned. -The only fields that the routines may examine in the <a href="../../api_c/dbt.html">DBT</a> -structures are <b>data</b> and <b>size</b> fields. -<p>An example prefix comparison routine follows: -<p><blockquote><pre>u_int32_t -compare_prefix(dbp, a, b) - DB *dbp; - const DBT *a, *b; -{ - size_t cnt, len; - u_int8_t *p1, *p2; -<p> - cnt = 1; - len = a->size > b->size ? b->size : a->size; - for (p1 = - a->data, p2 = b->data; len--; ++p1, ++p2, ++cnt) - if (*p1 != *p2) - return (cnt); - /* - * They match up to the smaller of the two sizes. - * Collate the longer after the shorter. - */ - if (a->size < b->size) - return (a->size + 1); - if (b->size < a->size) - return (b->size + 1); - return (b->size); -}</pre></blockquote> -<p>The usefulness of this functionality is data dependent, but in some data -sets can produce significantly reduced tree sizes and faster search times. -<table><tr><td><br></td><td width="1%"><a href="../../ref/am_conf/bt_compare.html"><img src="../../images/prev.gif" alt="Prev"></a><a href="../../ref/toc.html"><img src="../../images/ref.gif" alt="Ref"></a><a href="../../ref/am_conf/bt_minkey.html"><img src="../../images/next.gif" alt="Next"></a> -</td></tr></table> -<p><font size=1><a href="http://www.sleepycat.com">Copyright Sleepycat Software</a></font> -</body> -</html> |