gsg_txn/CXX/autocommit.html

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          <th colspan="3" align="center">Auto Commit</th>
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            <h2 class="title" style="clear: both"><a id="autocommit"></a>Auto Commit</h2>
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      <p>
            While transactions are frequently used to provide atomicity to
            multiple database

            operations, it is sometimes necessary to perform
            a single database

            operation under the control of a transaction.
            Rather than force you to obtain a transaction, perform the single
            write operation, and then either commit or abort the transaction,
            you can automatically group this sequence of events using
            <span class="emphasis"><em>auto commit</em></span>.
        </p>
      <p>
            To use auto commit:
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            <p>
                        Open your environment and your databases

                        so that they support
                    transactions.  See <a class="xref" href="enabletxn.html" title="Chapter 2. Enabling Transactions">Enabling Transactions</a>
                    for details.
                </p>
            <p>
                    Note that frequently auto commit is used for the environment
                    or database open.  To use auto commit for either your
                    environment or database open, specify
                    <code class="literal">DB_AUTO_COMMIT</code> to the


                    <code class="methodname">DbEnv::set_flags()</code>
                    or

                    <code class="methodname">Db::open()</code>
                    method. If you specify auto commit for the environment
                    open, then you do not need to also specify auto commit
                    for the database open.
                </p>
          </li>
          <li>
            <p>
                    Do not provide a transactional handle to the method that is
                    performing the database

                    write operation.
                </p>
          </li>
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      <p>
            Note that auto commit is not available for cursors. You must always
            open your cursor using a transaction if you want the cursor's
            operations to be transactional protected. See
            <a class="xref" href="txncursor.html" title="Transactional Cursors">Transactional Cursors</a> for details on using
            transactional cursors.
        </p>
      <div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
        <h3 class="title">Note</h3>
        <p>
                Never have more than one active transaction in your thread
                at a time. This is especially a problem if you mix an
                explicit transaction with another operation that uses auto
                commit. Doing so can result in undetectable deadlocks.
            </p>
      </div>
      <p>
            For example, the following uses auto commit to perform the database write operation:
        </p>
      <pre class="programlisting">#include "db_cxx.h"

...

int main(void)
{
    u_int32_t env_flags = DB_CREATE     |  // If the environment does not
                                           // exist, create it.
                          DB_INIT_LOCK  |  // Initialize locking
                          DB_INIT_LOG   |  // Initialize logging
                          DB_INIT_MPOOL |  // Initialize the cache
                          DB_INIT_TXN;     // Initialize transactions

    u_int32_t db_flags = DB_CREATE | DB_AUTO_COMMIT;
    Db *dbp = NULL;
    const char *file_name = "mydb.db";
    const char *keystr ="thekey";
    const char *datastr = "thedata";

    std::string envHome("/export1/testEnv");
    DbEnv myEnv(0);

    try {

        myEnv.open(envHome.c_str(), env_flags, 0);
        dbp = new Db(&amp;myEnv, 0);

        // Open the database. Note that we are using auto commit for
        // the open, so the database is able to support transactions.
        dbp-&gt;open(NULL,       // Txn pointer
                  file_name,  // File name
                  NULL,       // Logical db name */
                  DB_BTREE,   // Database type (using btree)
                  db_flags,   // Open flags
                  0);         // File mode. Using defaults

        Dbt key, data;
        key.set_data(keystr);
        key.set_size((strlen(keystr) + 1) * sizeof(char));
        key.set_data(datastr);
        key.set_size((strlen(datastr) + 1) * sizeof(char));

        // Perform the write. Because the database was opened to support
        // auto commit, this write is performed using auto commit.
        db-&gt;put(NULL, &amp;key, &amp;data, 0);

    } catch(DbException &amp;e) {
        std::cerr &lt;&lt; "Error opening database and environment: "
                  &lt;&lt; file_name &lt;&lt; ", "
                  &lt;&lt; envHome &lt;&lt; std::endl;
        std::cerr &lt;&lt; e.what() &lt;&lt; std::endl;
    }

    try {
        if (dbp != NULL)
            dbp-&gt;close(0);
        myEnv.close(0);
    } catch(DbException &amp;e) {
        std::cerr &lt;&lt; "Error closing database and environment: "
                  &lt;&lt; file_name &lt;&lt; ", "
                  &lt;&lt; envHome &lt;&lt; std::endl;
        std::cerr &lt;&lt; e.what() &lt;&lt; std::endl;
        return (EXIT_FAILURE);
    }

    return (EXIT_SUCCESS);
} </pre>
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