Import BSDDB 4.7.25 (as of svn r89086)
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Zachary Ware
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docs/api_cxx/memp_fget.html
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docs/api_cxx/memp_fget.html
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<!--$Id: memp_fget.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::get</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::get</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::get(db_pgno_t *pgnoaddr,
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DbTxn *txnid, u_int32_t flags, void **pagep);
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</pre></b>
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<hr size=1 noshade>
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<b>Description: DbMpoolFile::get</b>
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<p>The DbMpoolFile::get method returns pages from the cache.</p>
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<p>All pages returned by DbMpoolFile::get will be retained (that is,
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<i>pinned</i>), in the pool until a subsequent call to
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<a href="../api_cxx/memp_fput.html">DbMpoolFile::put</a>.</p>
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<p>The returned page is <b>size_t</b> type aligned.</p>
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<p>Fully or partially created pages have all their bytes set to a nul byte,
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unless the <a href="../api_cxx/memp_set_clear_len.html">DbMpoolFile::set_clear_len</a> method was called to specify other
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behavior before the file was opened.</p>
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<a name="2"><!--meow--></a>
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<p>The DbMpoolFile::get method
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will either return DB_PAGE_NOTFOUND or
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throw an exception that encapsulates DB_PAGE_NOTFOUND if the requested page does not exist and DB_MPOOL_CREATE was
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not set.
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Unless otherwise specified, the DbMpoolFile::get 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>flags</b><ul compact><li>The <b>flags</b> parameter must be set to 0 or by bitwise inclusively <b>OR</b>'ing together one
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or more of the following values:
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<br>
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<b><a name="DB_MPOOL_CREATE">DB_MPOOL_CREATE</a></b><ul compact><li>If the specified page does not exist, create it. In this case, the
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<a href="memp_register.html#pgin">pgin</a> method, if specified, is
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called.</ul>
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<b><a name="DB_MPOOL_DIRTY">DB_MPOOL_DIRTY</a></b><ul compact><li>The page will be modified and must be written to the source file before
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being evicted from the pool. For files open with the
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<a href="../api_cxx/db_open.html#DB_MULTIVERSION">DB_MULTIVERSION</a> flag set, a new copy of the page will be made
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if this is the first time the specified transaction is modifying it.</ul>
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<b><a name="DB_MPOOL_EDIT">DB_MPOOL_EDIT</a></b><ul compact><li>The page will be modified and must be written to the source file before
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being evicted from the pool. No copy of the page will be made, regardless
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of the <a href="../api_cxx/db_open.html#DB_MULTIVERSION">DB_MULTIVERSION</a> setting. This flag is only intended for
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use in situations where a transaction handle is not available, such as during
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aborts or recovery.</ul>
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<b><a name="DB_MPOOL_LAST">DB_MPOOL_LAST</a></b><ul compact><li>Return the last page of the source file, and copy its page number into
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the memory location to which <b>pgnoaddr</b> refers.</ul>
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<b><a name="DB_MPOOL_NEW">DB_MPOOL_NEW</a></b><ul compact><li>Create a new page in the file, and copy its page number into the memory
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location to which <b>pgnoaddr</b> refers. In this case, the
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<a href="memp_register.html#pgin">pgin</a> method, if specified, is
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<b>not</b> called.</ul>
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<br>
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<p>The DB_MPOOL_CREATE, DB_MPOOL_LAST, and
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DB_MPOOL_NEW flags are mutually exclusive.</p></ul>
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<b>pagep</b><ul compact><li>The <b>pagep</b> parameter references memory into which
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a pointer to the returned page is copied.</ul>
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<b>pgnoaddr</b><ul compact><li>If the <b>flags</b> parameter is set to DB_MPOOL_LAST or
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DB_MPOOL_NEW, the page number of the created page is copied
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into the memory location to which the <b>pgnoaddr</b> parameter
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refers. Otherwise, the <b>pgnoaddr</b> parameter is the page to
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create or retrieve.
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<p><b>Page numbers begin at 0; that is, the first page in the file is page
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number 0, not page number 1.</b></p></ul>
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<b>txnid</b><ul compact><li>If the operation is part of an application-specified
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transaction, the <b>txnid</b> parameter is a transaction handle
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returned from <a href="../api_cxx/txn_begin.html">DbEnv::txn_begin</a>; otherwise NULL. A transaction is
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required if the file is open for multiversion concurrency control by
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passing <a href="../api_cxx/db_open.html#DB_MULTIVERSION">DB_MULTIVERSION</a> to <a href="../api_cxx/memp_fopen.html">DbMpoolFile::open</a> and the
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DB_MPOOL_DIRTY, DB_MPOOL_CREATE or
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DB_MPOOL_NEW flags were specified. Otherwise it is ignored.</ul>
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<br>
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<br><b>Errors</b>
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<p>The DbMpoolFile::get method
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may fail and throw
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<a href="../api_cxx/except_class.html">DbException</a>,
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encapsulating one of the following non-zero errors, or return one of
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the following non-zero errors:</p>
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<br>
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<b>EACCES</b><ul compact><li>The DB_MPOOL_DIRTY or DB_MPOOL_EDIT flag was set and
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the source file was not opened for writing.</ul>
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<br>
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<br>
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<b>EAGAIN</b><ul compact><li>The page reference count has overflowed. (This should never happen
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unless there is a bug in the application.)</ul>
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<br>
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<br>
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<b>EINVAL</b><ul compact><li>If the DB_MPOOL_NEW flag was set, and the source file was not
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opened for writing;
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more than one of DB_MPOOL_CREATE, DB_MPOOL_LAST, and
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DB_MPOOL_NEW was set.; or if an
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invalid flag value or parameter was specified.</ul>
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<br>
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<br>
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<b>DB_LOCK_DEADLOCK</b><ul compact><li>For transactions configured with <a href="../api_cxx/txn_begin.html#DB_TXN_SNAPSHOT">DB_TXN_SNAPSHOT</a>, the page has
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been modified since the transaction began.</ul>
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<br>
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<p>If the cache is full, and no more pages will fit in the pool, the DbMpoolFile::get method will fail and
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either return ENOMEM or
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throw a DbMemoryException.</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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