93 lines
4.4 KiB
HTML
93 lines
4.4 KiB
HTML
<!--$Id: memp_set_fileid.html 63573 2008-05-23 21:43:21Z trent.nelson $-->
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<!--Copyright (c) 1997,2008 Oracle. All rights reserved.-->
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<!--See the file LICENSE for redistribution information.-->
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<html>
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<head>
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<title>Berkeley DB: DbMpoolFile::set_fileid</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,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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<table width="100%"><tr valign=top>
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<td>
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<b>DbMpoolFile::set_fileid</b>
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</td>
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<td align=right>
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<a href="../api_cxx/api_core.html"><img src="../images/api.gif" alt="API"></a>
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<a href="../ref/toc.html"><img src="../images/ref.gif" alt="Ref"></a></td>
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</tr></table>
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<hr size=1 noshade>
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<tt>
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<b><pre>
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#include <db_cxx.h>
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<p>
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int
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DbMpoolFile::set(u_int8_t *fileid);
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<p>
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int DbMpoolFile::get_fileid(u_int8_t *fileid);
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</pre></b>
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<hr size=1 noshade>
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<b>Description: DbMpoolFile::set_fileid</b>
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<p>The DbMpoolFile::set_fileid method specifies a unique identifier for the file.
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(The shared memory buffer pool functions must be able to uniquely
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identify files in order that multiple processes wanting to share a file
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will correctly identify it in the pool.)</p>
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<p>On most UNIX/POSIX systems, the <b>fileid</b> field will not need to
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be set, and the memory pool functions will use the file's device and
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inode numbers for this purpose. On Windows systems, the memory pool
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functions use the values returned by GetFileInformationByHandle() by
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default -- these values are known to be constant between processes and
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over reboot in the case of NTFS (in which they are the NTFS MFT
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indices).</p>
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<p>On other filesystems (for example, FAT or NFS), these default values
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are not necessarily unique between processes or across system reboots.
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<b>Applications wanting to maintain a shared memory buffer pool
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between processes or across system reboots, in which the pool contains
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pages from files stored on such filesystems, must specify a unique file
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identifier using the DbMpoolFile::set_fileid method, and each process opening
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the file must provide the same unique identifier.</b></p>
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<p>This call should not be necessary for most applications. Specifically,
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it is not necessary if the memory pool is not shared between processes
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and is reinstantiated after each system reboot, if the application is
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using the Berkeley DB access methods instead of calling the pool functions
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explicitly, or if the files in the memory pool are stored on filesystems
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in which the default values as described previously are invariant
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between process and across system reboots.</p>
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<p>The DbMpoolFile::set_fileid method configures a file in the memory pool, not only
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operations performed using the specified <a href="../api_cxx/mempfile_class.html">DbMpoolFile</a> handle.</p>
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<p>The DbMpoolFile::set_fileid method may not be called after the <a href="../api_cxx/memp_fopen.html">DbMpoolFile::open</a> method is
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called.
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</p>
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<p>The DbMpoolFile::set_fileid method
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either returns a non-zero error value
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or throws an exception that encapsulates a non-zero error value on
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failure, and returns 0 on success.
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</p>
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<b>Parameters</b> <br>
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<b>fileid</b><ul compact><li>The <b>fileid</b> parameter is the unique identifier for the file.
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Unique file identifiers must be a DB_FILE_ID_LEN length array of bytes.</ul>
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<br>
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<hr size=1 noshade>
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<b>Description: DbMpoolFile::get_fileid</b>
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<p>The DbMpoolFile::get_fileid method copies the file's identifier into the
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memory location referenced by <b>fileid</b>.</p>
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<p>The DbMpoolFile::get_fileid method
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either returns a non-zero error value
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or throws an exception that encapsulates a non-zero error value on
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failure, and returns 0 on success.
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</p>
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<p>The DbMpoolFile::get_fileid method may be called at any time during the life of the
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application.</p>
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<hr size=1 noshade>
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<br><b>Class</b>
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<a href="../api_cxx/env_class.html">DbEnv</a>, <a href="../api_cxx/mempfile_class.html">DbMpoolFile</a>
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<br><b>See Also</b>
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<a href="../api_cxx/memp_list.html">Memory Pools and Related Methods</a>
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</tt>
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<table width="100%"><tr><td><br></td><td align=right>
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<a href="../api_cxx/api_core.html"><img src="../images/api.gif" alt="API"></a><a href="../ref/toc.html"><img src="../images/ref.gif" alt="Ref"></a>
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</td></tr></table>
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<p><font size=1>Copyright (c) 1996,2008 Oracle. All rights reserved.</font>
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</body>
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</html>
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