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<p>Library Version 18.1.40</p>
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<h2 class="title" style="clear: both"><a id="txn_config"></a>Configuring transactions</h2>
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<p>
The application may change the number of simultaneous
outstanding transactions supported by the Berkeley DB
environment by calling the <a href="../api_reference/C/envset_tx_max.html" class="olink">DB_ENV->set_tx_max()</a> method. This will
also set the size of the underlying transaction subsystem's
region. When the number of outstanding transactions is
reached, additional calls to <a href="../api_reference/C/txnbegin.html" class="olink">DB_ENV->txn_begin()</a> will fail until some
active transactions complete.
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The application can limit how long a transaction runs or
blocks on contested resources. The <a href="../api_reference/C/envset_timeout.html" class="olink">DB_ENV->set_timeout()</a> method
specifies the length of the timeout. This value is checked
whenever deadlock detection is performed or when the
transaction is about to block on a lock that cannot be
immediately granted. Because timeouts are only checked at
these times, the accuracy of the timeout depends on how often
deadlock detection is performed or how frequently the
transaction blocks.
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There is an additional parameter used in configuring
transactions; the <a href="../api_reference/C/envset_flags.html#envset_flags_DB_TXN_NOSYNC" class="olink">DB_TXN_NOSYNC</a>. Setting the <a href="../api_reference/C/envset_flags.html#envset_flags_DB_TXN_NOSYNC" class="olink">DB_TXN_NOSYNC</a>
flag to <a href="../api_reference/C/envset_flags.html" class="olink">DB_ENV->set_flags()</a> when opening a transaction region
changes the behavior of transactions to not write or
synchronously flush the log during transaction commit.
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This change may significantly increase application
transactional throughput. However, it means that although
transactions will continue to exhibit the ACI (atomicity,
consistency, and isolation) properties, they will not have D
(durability). Database integrity will be maintained, but it is
possible that some number of the most recently committed
transactions may be undone during recovery instead of being
redone.
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