docs/gsg_txn/JAVA/nodurabletxn.html

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  17         <p>Library Version 11.2.5.3</p>
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  21           <th colspan="3" align="center">Non-Durable Transactions</th>
  22         </tr>
  23         <tr>
  24           <td width="20%" align="left"><a accesskey="p" href="usingtxns.html">Prev</a> </td>
  25           <th width="60%" align="center">Chapter 3. Transaction Basics</th>
  26           <td width="20%" align="right"> <a accesskey="n" href="abortresults.html">Next</a></td>
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  34           <div>
  35             <h2 class="title" style="clear: both"><a id="nodurabletxn"></a>Non-Durable Transactions</h2>
  36           </div>
  37         </div>
  38       </div>
  39       <p>
  40             As previously noted, by default transaction commits are
  41             durable because they cause the modifications performed
  42             under the transaction to be synchronously recorded in
  43             your on-disk log files.  However, it is possible to use
  44             non-durable transactions.
  45         </p>
  46       <p>
  47             You may want non-durable transactions for performance
  48             reasons. For example, you might be using transactions
  49             simply for the isolation guarantee.
  50
  51             <span>
  52             In this case, you might
  53             not want a durability guarantee and so you may want to
  54             prevent the disk I/O that normally accompanies a
  55             transaction commit.
  56             </span>
  57
  58         </p>
  59       <p>
  60             There are several ways to remove the durability guarantee
  61             for your transactions:
  62         </p>
  63       <div class="itemizedlist">
  64         <ul type="disc">
  65           <li>
  66             <p>
  67                     Specify
  68
  69                         <span>
  70                             <code class="literal">true</code> to the
  71                             <code class="methodname">EnvironmentConfig.setTxnNoSync()</code>
  72                             method.
  73                         </span>
  74                      This causes DB to not synchronously force any log
  75                      data to disk upon transaction commit.  That is, the modifications are held entirely
  76                      in the in-memory cache and the logging information is not forced to the filesystem for
  77                      long-term storage.
  78                      Note, however, that the logging
  79                      data will eventually make it to the filesystem (assuming no
  80                      application or OS crashes) as a part of DB's
  81                      management of its logging buffers and/or cache.
  82                </p>
  83             <p>
  84                         This form of a commit provides a weak durability
  85                         guarantee because data loss can occur due to
  86                         an application<span>, JVM,</span>
  87                         or OS crash.
  88                 </p>
  89             <p>
  90                     This behavior is specified on a per-environment
  91                     handle basis.  In order for your application to exhibit consistent
  92                     behavior, you need to specify this
  93
  94                         <span>method</span>
  95                     for all of the environment handles used in your application.
  96                 </p>
  97             <p>
  98                     You can achieve this behavior on a transaction by transaction basis by
  99
 100
 101                         <span>
 102                             using <code class="methodname">Transaction.commitNoSync()</code>
 103
 104                             to commit your transaction, or by specifying <code class="literal">true</code> to the
 105                             <code class="methodname">TransactionConfig.setNoSync()</code> method when starting the
 106                             transaction.
 107                         </span>
 108
 109                 </p>
 110           </li>
 111           <li>
 112             <p>
 113                     Specify
 114
 115
 116                         <span>
 117                             <code class="literal">true</code> to the
 118                             <code class="methodname">EnvironmentConfig.setTxnWriteNoSync()</code>
 119                             method.
 120                         </span>
 121
 122                         This causes
 123                         <span>
 124                             logging
 125                         </span>
 126                         data to be synchronously
 127                         written to the OS's file system buffers upon
 128                         transaction commit. The data will eventually be
 129                         written to disk, but this occurs when the
 130                         operating system chooses to schedule the
 131                         activity; the transaction commit can complete
 132                         successfully before this disk I/O is performed
 133                         by the OS.
 134                    </p>
 135             <p>
 136                             This  form of commit protects you against application
 137                             <span>and JVM</span> crashes, but not against OS
 138                             crashes.  This method offers less room for the possibility of data loss than does
 139
 140                             <span><code class="methodname">EnvironmentConfig.setTxnNoSync()</code>.</span>
 141                 </p>
 142             <p>
 143                     This behavior is specified on a per-environment
 144                     handle basis.  In order for your application to exhibit consistent
 145                     behavior, you need to specify this
 146
 147                         <span>method</span>
 148                     for all of the environment handles used in your application.
 149                 </p>
 150             <p>
 151                     You can achieve this behavior on a transaction by transaction basis by
 152                         <span>
 153                             using <code class="methodname">Transaction.commitWriteNoSync()</code>
 154                             to commit your transaction, or by specifying <code class="literal">true</code> to
 155                             <code class="methodname">TransactionConfig.setWriteNoSync()</code> method when starting the
 156                             transaction.
 157                         </span>
 158                 </p>
 159           </li>
 160           <li>
 161             <p>
 162                     Maintain your logs entirely in-memory. In this
 163                     case, your logs are never written to disk. The
 164                     result is that you lose all durability guarantees.
 165                     See
 166                     <a class="xref" href="logconfig.html#inmemorylogging" title="Configuring In-Memory Logging">Configuring In-Memory Logging</a>
 167                     for more information.
 168                 </p>
 169           </li>
 170         </ul>
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