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2.9 KiB
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<!--$Id: logrec.so,v 10.23 2000/12/04 18:05:41 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: Logical record numbers</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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<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><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/select.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/pagesize.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>Logical record numbers</h1>
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<p>The Berkeley DB Btree, Queue and Recno access methods can operate on logical
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record numbers. In all cases for the Queue and Recno access methods,
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and in some cases with the Btree access method, a record number is
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specified to reference a specific key/data pair. In the case of Btree
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supporting duplicate data items, the logical record number refers to a
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key and all of its data items.
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<p>Record numbers are 32-bit unsigned types, which limits the number of
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logical records in a database to 4,294,967,296. The first record in the
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database is record number 1.
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<p>Record numbers in Recno databases can be configured to run in either
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mutable or fixed mode: mutable, where logical record numbers change as
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records are deleted or inserted, and fixed, where record numbers never
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change regardless of the database operation. Record numbers in Btree
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databases are always mutable, and as records are deleted or inserted, the
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logical record number for other records in the database can change. See
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<a href="../../ref/am_conf/renumber.html">Logically renumbering records</a> for
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more information.
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<p>Record numbers in Queue databases are always fixed, and never change
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regardless of the database operation.
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<p>Configuring Btree databases to support record numbers can severely limit
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the throughput of applications with multiple concurrent threads writing
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the database, because locations used to store record counts often become
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hot spots that many different threads all need to update.
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<table><tr><td><br></td><td width="1%"><a href="../../ref/am_conf/select.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/pagesize.html"><img src="../../images/next.gif" alt="Next"></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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