74 lines
3.2 KiB
HTML
74 lines
3.2 KiB
HTML
<!--$Id: db_set_h_hash.html 63573 2008-05-23 21:43:21Z trent.nelson $-->
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<!--Copyright (c) 1997,2008 Oracle. All rights reserved.-->
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<!--See the file LICENSE for redistribution information.-->
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<html>
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<head>
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<title>Berkeley DB: DB->set_h_hash</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,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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<table width="100%"><tr valign=top>
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<td>
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<b>DB->set_h_hash</b>
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</td>
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<td align=right>
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<a href="../api_c/api_core.html"><img src="../images/api.gif" alt="API"></a>
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<a href="../ref/toc.html"><img src="../images/ref.gif" alt="Ref"></a></td>
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</tr></table>
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<hr size=1 noshade>
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<tt>
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<b><pre>
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#include <db.h>
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<p>
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int
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DB->set_h_hash(DB *db,
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u_int32_t (*h_hash_fcn)(DB *, const void *bytes, u_int32_t length));
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</pre></b>
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<hr size=1 noshade>
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<b>Description: DB->set_h_hash</b>
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<p>Set a user-defined hash function; if no hash function is specified, a
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default hash function is used. Because no hash function performs
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equally well on all possible data, the user may find that the built-in
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hash function performs poorly with a particular data set.</p>
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<p>The DB->set_h_hash method configures operations performed using the specified
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<a href="../api_c/db_class.html">DB</a> handle, not all operations performed on the underlying
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database.</p>
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<p>The DB->set_h_hash method may not be called after the <a href="../api_c/db_open.html">DB->open</a> method is called.
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If the database already exists when
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<a href="../api_c/db_open.html">DB->open</a> is called, the information specified to DB->set_h_hash must
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be the same as that historically used to create the database or
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corruption can occur.</p>
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<p>The DB->set_h_hash method
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returns a non-zero error value on failure
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and 0 on success.
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</p>
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<b>Parameters</b> <br>
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<b>h_hash_fcn</b><ul compact><li>The <b>h_hash_fcn</b> parameter is the application-specified hash function.
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<p>Application-specified hash functions take a pointer to a byte string and
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a length as parameters, and return a value of type <b>u_int32_t</b>.
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The hash function must handle any key values used by the application
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(possibly including zero-length keys).</p></ul>
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<br>
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<br><b>Errors</b>
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<p>The DB->set_h_hash method
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may fail and return one of the following non-zero errors:</p>
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<br>
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<b>EINVAL</b><ul compact><li>If the method was called after <a href="../api_c/db_open.html">DB->open</a> was called; the
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specified hash function differs from the hash function with which the
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database was created; or if an
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invalid flag value or parameter was specified.</ul>
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<br>
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<hr size=1 noshade>
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<br><b>Class</b>
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<a href="../api_c/db_class.html">DB</a>
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<br><b>See Also</b>
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<a href="../api_c/db_list.html">Databases and Related Methods</a>
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</tt>
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<table width="100%"><tr><td><br></td><td align=right>
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<a href="../api_c/api_core.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>Copyright (c) 1996,2008 Oracle. All rights reserved.</font>
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</body>
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</html>
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