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<!--$Id: remote.so,v 11.5 2000/03/18 21:43:12 bostic Exp $-->
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<!--Copyright 1997, 1998, 1999, 2000 by Sleepycat Software, Inc.-->
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<!--All rights reserved.-->
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<html>
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<head>
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<title>Berkeley DB Reference Guide: Remote filesystems</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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</head>
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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>Environment</dl></h3></td>
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<td width="1%"><a href="../../ref/env/region.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/env/open.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>Remote filesystems</h1>
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<p>When regions are backed by the filesystem, it is a common error to attempt
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to create Berkeley DB environments backed by remote file systems such as the
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Network File System (NFS) or the Andrew File System (AFS). Remote
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filesystems rarely support mapping files into process memory, and even
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more rarely support correct semantics for mutexes after the attempt
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succeeds. For this reason, we strongly recommend that the database
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environment directory reside in a local filesystem.
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<p>For remote file systems that do allow system files to be mapped into
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process memory, home directories accessed via remote file systems cannot
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be used simultaneously from multiple clients. None of the commercial
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remote file systems available today implement coherent, distributed shared
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memory for remote-mounted files. As a result, different machines will
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see different versions of these shared regions and the system behavior is
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undefined.
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<p>Databases, log files and temporary files may be placed on remote
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filesystems, <b>as long as the remote filesystem fully supports
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standard POSIX filesystem semantics</b>, although the application may incur
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a performance penalty for doing so. Obviously, NFS-mounted databases
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cannot be accessed from more than one Berkeley DB environment (and therefore
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from more than one system), at a time since no Berkeley DB database may be
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accessed from more than one Berkeley DB environment at a time.
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<p><dl compact>
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<p><dt>Linux note:<dd>Some Linux releases are known to not support complete semantics for the
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POSIX fsync call on NFS-mounted filesystems. No Berkeley DB files should be
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placed on NFS-mounted filesystems on these systems.
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</dl>
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<table><tr><td><br></td><td width="1%"><a href="../../ref/env/region.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/env/open.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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</body>
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</html>
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