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<title>Berkeley DB Reference Guide: Logical record numbers</title>
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<td><h3><dl><dt>Berkeley DB Reference Guide:<dd>Access Methods</dl></h3></td>
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<h1 align=center>Logical record numbers</h1>
<p>The Berkeley DB Btree, Queue and Recno access methods can operate on logical
record numbers. In all cases for the Queue and Recno access methods,
and in some cases with the Btree access method, a record number is
specified to reference a specific key/data pair. In the case of Btree
supporting duplicate data items, the logical record number refers to a
key and all of its data items.
<p>Record numbers are 32-bit unsigned types, which limits the number of
logical records in a database to 4,294,967,296. The first record in the
database is record number 1.
<p>Record numbers in Recno databases can be configured to run in either
mutable or fixed mode: mutable, where logical record numbers change as
records are deleted or inserted, and fixed, where record numbers never
change regardless of the database operation. Record numbers in Btree
databases are always mutable, and as records are deleted or inserted, the
logical record number for other records in the database can change. See
<a href="../../ref/am_conf/renumber.html">Logically renumbering records</a> for
more information.
<p>Record numbers in Queue databases are always fixed, and never change
regardless of the database operation.
<p>Configuring Btree databases to support record numbers can severely limit
the throughput of applications with multiple concurrent threads writing
the database, because locations used to store record counts often become
hot spots that many different threads all need to update.
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