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<b>DB_SEQUENCE->get</b>
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<b><pre>
#include <db.h>
<p>
int
DB_SEQUENCE->get(DB_SEQUENCE *seq,
DB_TXN *txnid, int32_t delta, db_seq_t *retp, u_int32_t flags);
</pre></b>
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<b>Description: DB_SEQUENCE->get</b>
<p>The DB_SEQUENCE->get method returns the next available element in the sequence
and changes the sequence value by <b>delta</b>. The value of
<b>delta</b> must be greater than zero. If there are enough cached
values in the sequence handle then they will be returned. Otherwise the
next value will be fetched from the database and incremented
(decremented) by enough to cover the <b>delta</b> and the next batch
of cached values.</p>
<p>For maximum concurrency a non-zero cache size should be specified prior
to opening the sequence handle and <a href="../../db4-devel-4.7.25/api_c/env_set_flags.html#DB_TXN_NOSYNC">DB_TXN_NOSYNC</a> should be
specified for each DB_SEQUENCE->get method call.</p>
<p>By default, sequence ranges do not wrap; to cause the sequence to wrap
around the beginning or end of its range, specify the <a href="../../db4-devel-4.7.25/api_c/seq_set_flags.html#DB_SEQ_WRAP">DB_SEQ_WRAP</a>
flag to the <a href="../../db4-devel-4.7.25/api_c/seq_set_flags.html">DB_SEQUENCE->set_flags</a> method.</p>
<p>The DB_SEQUENCE->get method will return EINVAL if the record in the database is not a valid sequence
record, or the sequence has reached the beginning or end of its range
and is not configured to wrap.
</p>
<b>Parameters</b> <br>
<b>delta</b><ul compact><li>Specifies the amount to increment or decrement the sequence.</ul>
<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
or more of the following values:
<br>
<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>
argument is NULL but the operation occurs to a transactional database),
do not synchronously flush the log when the transaction commits.</ul>
<br></ul>
<b>retp</b><ul compact><li><b>retp</b> points to the memory to hold the return value from
the sequence.</ul>
<b>txnid</b><ul compact><li>If the operation is part of an application-specified transaction, the
<b>txnid</b> parameter is a transaction handle returned from
<a href="../../db4-devel-4.7.25/api_c/txn_begin.html">DB_ENV->txn_begin</a>; if the operation is part of a Berkeley DB Concurrent Data Store group, the
<b>txnid</b> parameter is a handle returned from
<a href="../../db4-devel-4.7.25/api_c/env_cdsgroup_begin.html">DB_ENV->cdsgroup_begin</a>; otherwise NULL.
If no transaction handle is
specified, but the
operation occurs in a transactional
database,
the operation will be implicitly transaction protected.
No <b>txnid</b> handle may be specified if the sequence handle was
opened with a non-zero cache size.
<p>If the underlying database handle was opened in a transaction, calling
DB_SEQUENCE->get may result in changes to the sequence object; these
changes will be automatically committed in a transaction internal to the
Berkeley DB library. If the thread of control calling DB_SEQUENCE->get has
an active transaction, which holds locks on the same database as the
one in which the sequence object is stored, it is possible for a thread
of control calling DB_SEQUENCE->get to self-deadlock because the active
transaction's locks conflict with the internal transaction's locks.
For this reason, it is often preferable for sequence objects to be
stored in their own database.</p></ul>
<br>
<hr size=1 noshade>
<br><b>Class</b>
<a href="../../db4-devel-4.7.25/api_c/seq_class.html">DB_SEQUENCE</a>
<br><b>See Also</b>
<a href="../../db4-devel-4.7.25/api_c/seq_list.html">Sequences and Related Methods</a>
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