Import BSDDB 4.7.25 (as of svn r89086)
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Zachary Ware
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docs/api_c/seq_get.html
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docs/api_c/seq_get.html
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<!--$Id: seq_get.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: DB_SEQUENCE->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>DB_SEQUENCE->get</b>
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</td>
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<td align=right>
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<a href="../api_c/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.h>
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<p>
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int
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DB_SEQUENCE->get(DB_SEQUENCE *seq,
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DB_TXN *txnid, int32_t delta, db_seq_t *retp, u_int32_t flags);
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</pre></b>
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<hr size=1 noshade>
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<b>Description: DB_SEQUENCE->get</b>
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<p>The DB_SEQUENCE->get method returns the next available element in the sequence
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and changes the sequence value by <b>delta</b>. The value of
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<b>delta</b> must be greater than zero. If there are enough cached
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values in the sequence handle then they will be returned. Otherwise the
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next value will be fetched from the database and incremented
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(decremented) by enough to cover the <b>delta</b> and the next batch
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of cached values.</p>
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<p>For maximum concurrency a non-zero cache size should be specified prior
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to opening the sequence handle and <a href="../api_c/env_set_flags.html#DB_TXN_NOSYNC">DB_TXN_NOSYNC</a> should be
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specified for each DB_SEQUENCE->get method call.</p>
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<p>By default, sequence ranges do not wrap; to cause the sequence to wrap
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around the beginning or end of its range, specify the <a href="../api_c/seq_set_flags.html#DB_SEQ_WRAP">DB_SEQ_WRAP</a>
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flag to the <a href="../api_c/seq_set_flags.html">DB_SEQUENCE->set_flags</a> method.</p>
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<p>The DB_SEQUENCE->get method will return EINVAL if the record in the database is not a valid sequence
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record, or the sequence has reached the beginning or end of its range
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and is not configured to wrap.
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</p>
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<b>Parameters</b> <br>
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<b>delta</b><ul compact><li>Specifies the amount to increment or decrement the sequence.</ul>
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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_TXN_NOSYNC">DB_TXN_NOSYNC</a></b><ul compact><li>If the operation is implicitly transaction protected (the <b>txnid</b>
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argument is NULL but the operation occurs to a transactional database),
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do not synchronously flush the log when the transaction commits.</ul>
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<br></ul>
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<b>retp</b><ul compact><li><b>retp</b> points to the memory to hold the return value from
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the sequence.</ul>
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<b>txnid</b><ul compact><li>If the operation is part of an application-specified transaction, the
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<b>txnid</b> parameter is a transaction handle returned from
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<a href="../api_c/txn_begin.html">DB_ENV->txn_begin</a>; if the operation is part of a Berkeley DB Concurrent Data Store group, the
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<b>txnid</b> parameter is a handle returned from
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<a href="../api_c/env_cdsgroup_begin.html">DB_ENV->cdsgroup_begin</a>; otherwise NULL.
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If no transaction handle is
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specified, but the
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operation occurs in a transactional
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database,
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the operation will be implicitly transaction protected.
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No <b>txnid</b> handle may be specified if the sequence handle was
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opened with a non-zero cache size.
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<p>If the underlying database handle was opened in a transaction, calling
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DB_SEQUENCE->get may result in changes to the sequence object; these
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changes will be automatically committed in a transaction internal to the
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Berkeley DB library. If the thread of control calling DB_SEQUENCE->get has
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an active transaction, which holds locks on the same database as the
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one in which the sequence object is stored, it is possible for a thread
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of control calling DB_SEQUENCE->get to self-deadlock because the active
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transaction's locks conflict with the internal transaction's locks.
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For this reason, it is often preferable for sequence objects to be
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stored in their own database.</p></ul>
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<br>
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<hr size=1 noshade>
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<br><b>Class</b>
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<a href="../api_c/seq_class.html">DB_SEQUENCE</a>
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<br><b>See Also</b>
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<a href="../api_c/seq_list.html">Sequences 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_c/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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