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https://github.com/berkeleydb/libdb.git
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222 lines
7.3 KiB
HTML
222 lines
7.3 KiB
HTML
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<?xml version="1.0" encoding="UTF-8" standalone="no"?>
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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<html xmlns="http://www.w3.org/1999/xhtml">
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
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<title>Transactional Cursors</title>
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<link rel="stylesheet" href="gettingStarted.css" type="text/css" />
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<meta name="generator" content="DocBook XSL Stylesheets V1.73.2" />
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<link rel="start" href="index.html" title="Getting Started with Berkeley DB Transaction Processing" />
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<link rel="up" href="usingtxns.html" title="Chapter 3. Transaction Basics" />
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<link rel="prev" href="nestedtxn.html" title="Nested Transactions" />
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<link rel="next" href="txnindices.html" title="Secondary Indices with Transaction Applications" />
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</head>
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<body>
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<div xmlns="" class="navheader">
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<div class="libver">
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<p>Library Version 11.2.5.2</p>
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</div>
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<table width="100%" summary="Navigation header">
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<tr>
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<th colspan="3" align="center">Transactional Cursors</th>
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</tr>
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<tr>
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<td width="20%" align="left"><a accesskey="p" href="nestedtxn.html">Prev</a> </td>
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<th width="60%" align="center">Chapter 3. Transaction Basics</th>
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<td width="20%" align="right"> <a accesskey="n" href="txnindices.html">Next</a></td>
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</tr>
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</table>
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<hr />
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</div>
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<div class="sect1" lang="en" xml:lang="en">
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<div class="titlepage">
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<div>
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<div>
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<h2 class="title" style="clear: both"><a id="txncursor"></a>Transactional Cursors</h2>
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</div>
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</div>
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</div>
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<div class="toc">
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<dl>
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<dt>
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<span class="sect2">
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<a href="txncursor.html#dplcursors">Using Transactional DPL Cursors</a>
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</span>
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</dt>
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</dl>
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</div>
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<p>
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You can transaction-protect your cursor operations by
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specifying a transaction handle at the time that you create
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your cursor. Beyond that, you do not ever
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provide a transaction handle directly to a cursor method.
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</p>
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<p>
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Note that if you transaction-protect a cursor, then you must
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make sure that the cursor is closed before you either commit or
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abort the transaction. For example:
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</p>
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<pre class="programlisting">package db.txn;
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import com.sleepycat.db.Cursor;
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import com.sleepycat.db.Database;
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import com.sleepycat.db.DatabaseConfig;
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import com.sleepycat.db.DatabaseEntry;
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import com.sleepycat.db.DatabaseException;
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import com.sleepycat.db.Environment;
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import com.sleepycat.db.EnvironmentConfig;
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import com.sleepycat.db.LockMode;
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import com.sleepycat.db.OperationStatus;
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import com.sleepycat.db.Transaction;
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import java.io.File;
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import java.io.FileNotFoundException;
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...
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Database myDatabase = null;
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Environment myEnv = null;
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try {
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// Database and environment opens omitted
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String replacementData = "new data";
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Transaction txn = myEnv.beginTransaction(null, null);
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Cursor cursor = null;
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try {
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// Use the transaction handle here
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cursor = db.openCursor(txn, null);
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DatabaseEntry key, data;
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DatabaseEntry key, data;
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while(cursor.getNext(key, data, LockMode.DEFAULT) ==
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OperationStatus.SUCCESS) {
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data.setData(replacementData.getBytes("UTF-8"));
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// No transaction handle is used on the cursor read or write
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// methods.
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cursor.putCurrent(data);
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}
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cursor.close();
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cursor = null;
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txn.commit();
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txn = null;
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} catch (Exception e) {
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if (cursor != null) {
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cursor.close();
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}
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if (txn != null) {
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txn.abort();
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txn = null;
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}
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}
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} catch (DatabaseException de) {
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// Exception handling goes here
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} </pre>
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<div class="sect2" lang="en" xml:lang="en">
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<div class="titlepage">
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<div>
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<div>
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<h3 class="title"><a id="dplcursors"></a>Using Transactional DPL Cursors</h3>
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</div>
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</div>
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</div>
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<p>
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When using the DPL, you create the cursor using the entity
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class's primary or secondary index (see the
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<em class="citetitle">Getting Started with Berkeley DB for Java</em>
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guide for details). At the time that you create the cursor, you
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pass a transaction handle to the <code class="methodname">entities()</code>
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method, and this causes all subsequent operations performed
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using that cursor to be performed within the scope of the
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transaction.
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</p>
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<p>
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Note that if you are using a transaction-enabled store,
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then you must provide a transaction handle when you open
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your cursor.
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</p>
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<p>
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For example:
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</p>
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<pre class="programlisting">package persist.txn;
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import com.sleepycat.db.DatabaseException;
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import com.sleepycat.db.Environment;
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import com.sleepycat.db.EnvironmentConfig;
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import com.sleepycat.db.Transaction;
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import com.sleepycat.persist.EntityCursor;
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import com.sleepycat.persist.EntityStore;
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import com.sleepycat.persist.PrimaryIndex;
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import java.io.File;
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import java.io.FileNotFoundException;
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...
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Environment myEnv = null;
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EntityStore store = null;
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...
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// Store and environment open omitted, as is the DataAccessor
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// instantiation.
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...
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Transaction txn = myEnv.beginTransaction(null, null);
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PrimaryIndex<String,Inventory> pi =
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store.getPrimaryIndex(String.class, Inventory.class);
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EntityCursor<Inventory> pi_cursor = pi.entities(txn, null);
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try {
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for (Inventory ii : pi_cursor) {
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// do something with each object "ii"
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// A transactional handle is not required for any write
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// operations. All operations performed using this cursor
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// will be done within the scope of the transaction, txn.
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}
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pi_cursor.close();
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pi_cursor = null;
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txn.commit();
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txn = null;
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// Always make sure the cursor is closed when we are done with it.
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} catch (Exception e) {
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if (pi_cursor != null) {
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pi_cursor.close();
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}
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if (txn != null) {
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txn.abort();
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txn = null;
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}
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} </pre>
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</div>
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</div>
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<div class="navfooter">
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<hr />
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<table width="100%" summary="Navigation footer">
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|||
|
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<tr>
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|||
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<td width="40%" align="left"><a accesskey="p" href="nestedtxn.html">Prev</a> </td>
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|||
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<td width="20%" align="center">
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|||
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<a accesskey="u" href="usingtxns.html">Up</a>
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</td>
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|||
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<td width="40%" align="right"> <a accesskey="n" href="txnindices.html">Next</a></td>
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</tr>
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<tr>
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<td width="40%" align="left" valign="top">Nested Transactions </td>
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<td width="20%" align="center">
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<a accesskey="h" href="index.html">Home</a>
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</td>
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<td width="40%" align="right" valign="top"> Secondary Indices with Transaction Applications</td>
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</tr>
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</table>
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</div>
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</body>
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</html>
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