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<!--$Id: db_set_h_hash.so,v 10.18 2000/07/04 18:28:27 bostic Exp $-->
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<h1>Db.set_h_hash</h1>
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<h3><pre>
import com.sleepycat.db.*;
<p>
public interface DbHash
{
public abstract int hash(Db db, byte[] data, int len);
}
public class Db
{
public void set_h_hash(DbHash h_hash)
throws DbException;
...
}
</pre></h3>
<h1>Description</h1>
<p>Set a user defined hash method; if no hash method is specified, a default
hash method is used. Since no hash method performs equally well on all
possible data, the user may find that the built-in hash method performs
poorly with a particular data set. User specified hash functions must
take a pointer to a byte string and a length as arguments and return a
value of type
<b>int</b>.
The hash function must handle any key values used by the application
(possibly including zero-length keys).
<p>If a hash method is specified, <a href="../api_java/db_open.html">Db.open</a> will attempt to determine
if the hash method specified is the same as the one with which the database
was created, and will fail if it detects that it is not.
<p>The Db.set_h_hash interface may only be used to configure Berkeley DB before
the <a href="../api_java/db_open.html">Db.open</a> interface is called.
<p>The Db.set_h_hash method throws an exception that encapsulates a non-zero error value on
failure.
<h1>Errors</h1>
<p><dl compact>
<p><dt>EINVAL<dd>An invalid flag value or parameter was specified.
<p>Called after <a href="../api_java/db_open.html">Db.open</a> was called.
</dl>
<h3>Class</h3>
<a href="../api_java/db_class.html">Db</a>
<h1>See Also</h1>
<a href="../api_java/db_close.html">Db.close</a>,
<a href="../api_java/db_cursor.html">Db.cursor</a>,
<a href="../api_java/db_del.html">Db.del</a>,
<a href="../api_java/db_fd.html">Db.fd</a>,
<a href="../api_java/db_get.html">Db.get</a>,
<a href="../api_java/db_get_byteswapped.html">Db.get_byteswapped</a>,
<a href="../api_java/db_get_type.html">Db.get_type</a>,
<a href="../api_java/db_join.html">Db.join</a>,
<a href="../api_java/db_key_range.html">Db.key_range</a>,
<a href="../api_java/db_open.html">Db.open</a>,
<a href="../api_java/db_put.html">Db.put</a>,
<a href="../api_java/db_remove.html">Db.remove</a>,
<a href="../api_java/db_set_bt_minkey.html">Db.set_bt_minkey</a>,
<a href="../api_java/db_set_cachesize.html">Db.set_cachesize</a>,
<a href="../api_java/db_set_errcall.html">Db.set_errcall</a>,
<a href="../api_java/db_set_errpfx.html">Db.set_errpfx</a>,
<a href="../api_java/db_set_flags.html">Db.set_flags</a>,
<a href="../api_java/db_set_h_ffactor.html">Db.set_h_ffactor</a>,
<a href="../api_java/db_set_h_nelem.html">Db.set_h_nelem</a>,
<a href="../api_java/db_set_lorder.html">Db.set_lorder</a>,
<a href="../api_java/db_set_pagesize.html">Db.set_pagesize</a>,
<a href="../api_java/db_set_q_extentsize.html">Db.set_q_extentsize</a>,
<a href="../api_java/db_set_re_delim.html">Db.set_re_delim</a>,
<a href="../api_java/db_set_re_len.html">Db.set_re_len</a>,
<a href="../api_java/db_set_re_pad.html">Db.set_re_pad</a>,
<a href="../api_java/db_set_re_source.html">Db.set_re_source</a>,
<a href="../api_java/db_stat.html">Db.stat</a>,
<a href="../api_java/db_sync.html">Db.sync</a>,
<a href="../api_java/db_upgrade.html">Db.upgrade</a>
and
<a href="../api_java/db_verify.html">Db.verify</a>.
</tt>
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