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<title>Berkeley DB Reference Guide: Remote filesystems</title>
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<table width="100%"><tr valign=top>
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<td><h3><dl><dt>Berkeley DB Reference Guide:<dd>Environment</dl></h3></td>
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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 filesystems 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 filesystems that do allow system files to be mapped into
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process memory, home directories accessed via remote filesystems cannot
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be used simultaneously from multiple clients. None of the commercial
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remote filesystems available today implement coherent, distributed
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shared memory for remote-mounted files. As a result, different machines
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will see different versions of these shared regions, and the system
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behavior is 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
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incur a performance penalty for doing so). Obviously, NFS-mounted
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databases cannot be accessed from more than one Berkeley DB environment at a
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time (and therefore from more than one system), because no Berkeley DB
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database may be accessed from more than one Berkeley DB environment at a
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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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