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            <th width="60%" align="center">Chapter 3. Transaction Basics</th>
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              <h2 class="title" style="clear: both"><a id="maxtxns"></a>Configuring the Transaction Subsystem</h2>
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        <p>
              Most of the configuration activities that you need to perform
              for your transactional DB application will involve the
              locking and logging subsystems. See 
              <a class="xref" href="txnconcurrency.html" title="Chapter 4. Concurrency">Concurrency</a>
              and
              <a class="xref" href="filemanagement.html" title="Chapter 5. Managing DB Files">Managing DB Files</a>
              for details.
          </p>
        <p>
              However, there are a couple of things that you can do to
              configure your transaction subsystem directly. These things
              are:
          </p>
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            <li>
              <span>
                  <p>
                      
                      <span>
                          Configure 
                      </span>
                          
                      the maximum number of simultaneous
                      transactions needed by your application. 
                      In general, you should not need to do this unless you
                      use deeply nested transactions or you have many threads all
                      of which have active transactions. In addition, you may
                      need to configure a higher maximum number of transactions if you
                      are using snapshot isolation. See
                      <a class="xref" href="isolation.html#sisolation_maxtxn" title="Snapshot Isolation Transactional Requirements">Snapshot Isolation Transactional Requirements</a>
                      for details.
                  </p>
                  <p>
                      By default, your application can support 20 active
                      transactions. 
                  </p>
                  <p>
                      You can set the maximum number of simultaneous
                      transactions supported by your application using
                      
                      <span>
                          <code class="methodname">EnvironmentConfig.setTxnMaxActive()</code>.
                      </span>
                  </p>
                  <p>
                      If your application has exceeded this maximum value,
                      then any attempt to begin a new transaction will fail.
                  </p>
                  <p>
                      This value can also be set using the
                      <code class="literal">DB_CONFIG</code> file's
                      <code class="literal">set_tx_max</code> parameter. Remember that
                      the <code class="literal">DB_CONFIG</code> must reside in your
                      environment home directory.
                  </p>
  </span>
            </li>
            <li>
              <span>
                    <p>
                      <span>
                      Configure the timeout value for your transactions. 
                      </span>
                      
                      
                      This value represents the longest period of time a
                      transaction can be active. Note, however, that
                      transaction timeouts are checked only when DB
                      examines its lock tables for blocked locks
                      (see <a class="xref" href="blocking_deadlocks.html" title="Locks, Blocks, and Deadlocks">Locks, Blocks, and Deadlocks</a>
                      for more information). Therefore, a transaction's timeout can
                      have expired, but the application will not be notified until DB 
                      has a reason to examine its lock tables.
                  </p>
                  <p>
                      Be aware that some transactions may be
                      inappropriately timed out before the transaction has a
                      chance to complete. You should therefore use this
                      mechanism only if you know your application
                      might have unacceptably long transactions and
                      you want to make sure your application will
                      not stall during their execution.
                      (This might happen if, for example, your
                      transaction blocks or requests too much
                      data.)
                  </p>
                  <p>
                      Note that by default transaction timeouts are set to 0 seconds, which means that they never time
                      out.
                  </p>
                  <p>
                      To set the maximum timeout value for your transactions,
                      use  the
                              
                              
                              <span><code class="methodname">EnvironmentConfig.setTxnTimeout()</code></span>
                          method. This method configures the entire
                          environment; not just the handle used to set the
                          configuration. Further, this value may
                          be set at any time during the application's
                          lifetime. <span>(Use
                          <code class="methodname">Environment.setConfig()</code> to
                          set this value after the environment has been
                          opened.)</span>
                  </p>
                  <p>
                      This value can also be set using the
                      <code class="literal">DB_CONFIG</code> file's
                      <code class="literal">set_txn_timeout</code> parameter.
                  </p> 
                  
  </span>
            </li>
          </ul>
        </div>
        <p>
              For example:
          </p>
        <pre class="programlisting">package db.txn;
  
  import com.sleepycat.db.Environment;
  import com.sleepycat.db.EnvironmentConfig;
  import com.sleepycat.db.LockDetectMode;
  
  import java.io.File;
  import java.io.FileNotFoundException;
  
  ...
  
  Environment myEnv = null;
  try {
      EnvironmentConfig myEnvConfig = new EnvironmentConfig();
      myEnvConfig.setTransactional(true);
      myEnvConfig.setInitializeCache(true);
      myEnvConfig.setInitializeLocking(true);
      myEnvConfig.setInitializeLogging(true);
  
      // Configure a maximum transaction timeout of 1 second.
      myEnvConfig.setTxnTimeout(1000000);
      // Configure 40 maximum transactions.
      myEnv.setTxnMaxActive(40);
  
      myEnv = new Environment(new File("/my/env/home"),
                                myEnvConfig);
  
      // From here, you open your databases (or store), proceed with your 
      // database or store operations, and respond to deadlocks as is 
      // normal (omitted for brevity).
  
      ...</pre>
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