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2.5 KiB
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<!--$Id: extentsize.so,v 1.2 2000/11/20 21:45:19 bostic Exp $-->
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<!--Copyright 1997, 1998, 1999, 2000 by Sleepycat Software, Inc.-->
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<html>
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<head>
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<title>Berkeley DB Reference Guide: Selecting a Queue extent size</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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<a name="2"><!--meow--></a>
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<table><tr valign=top>
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<td><h3><dl><dt>Berkeley DB Reference Guide:<dd>Access Methods</dl></h3></td>
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<td width="1%"><a href="../../ref/am_conf/recno.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/re_source.html"><img src="../../images/next.gif" alt="Next"></a>
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</td></tr></table>
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<p>
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<h1 align=center>Selecting a Queue extent size</h1>
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<p>In Queue databases, records are allocated sequentially and directly
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mapped to an offset within the file storage for the database. As
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records are deleted from the Queue, pages will become empty and will
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not be reused in normal queue operations. To facilitate the reclamation
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of disk space a Queue may be partitioned into extents. Each extent is
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kept in a separate physical file. Extent files are automatically
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created as needed and destroyed when they are emptied of records.
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<p>The extent size specifies the number of pages that make up each extent.
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By default, if no extent size is specified, the Queue resides in a
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single file and disk space is not reclaimed. In choosing an extent size
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there is a tradeoff between the amount of disk space used and the
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overhead of creating and deleting files. If the extent size is too
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small, the system will pay a performance penalty, creating and deleting
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files frequently. In addition, if the active part of the queue spans
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many files, all those files will need to be open at the same time,
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consuming system and process file resources.
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<table><tr><td><br></td><td width="1%"><a href="../../ref/am_conf/recno.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/re_source.html"><img src="../../images/next.gif" alt="Next"></a>
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<p><font size=1><a href="http://www.sleepycat.com">Copyright Sleepycat Software</a></font>
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