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129 lines
4.7 KiB
HTML
129 lines
4.7 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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<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">#include "db_cxx.h"
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...
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int main(void)
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{
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// Environment and database opens omitted
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...
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DbTxn *txn = NULL;
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Dbc *cursorp = NULL;
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try {
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Dbt key, data;
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key.set_data(keystr);
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key.set_size((strlen(keystr) + 1) * sizeof(char));
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key.set_data(datastr);
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key.set_size((strlen(datastr) + 1) * sizeof(char));
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DbTxn *txn = NULL;
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myEnv.txn_begin(NULL, &txn, 0);
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try {
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// Get our cursor. Note that we pass the transaction handle
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// here.
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db.cursor(txn, &cursorp, 0);
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// Perform our operations. Note that we do not pass a
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// transaction handle here.
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char *replacementString = "new string";
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while (cursor->get(&key, &data, DB_NEXT) == 0) {
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data.set_data(void *)replacementString);
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data.set_size((strlen(replacementString) + 1) *
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sizeof(char));
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cursor->put(&key, &data, DB_CURRENT);
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}
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// We're done. Commit the transaction.
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cursor->close();
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txn->commit(0);
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} catch (DbException &e) {
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std::cerr << "Error in transaction: "
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<< e.what() << std::endl;
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cursor->close();
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txn->abort();
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}
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} catch(DbException &e) {
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std::cerr << "Error opening database and environment: "
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<< file_name << ", "
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<< envHome << std::endl;
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std::cerr << e.what() << std::endl;
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}
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return (EXIT_SUCCESS);
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} </pre>
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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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<tr>
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<td width="40%" align="left"><a accesskey="p" href="nestedtxn.html">Prev</a> </td>
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<td width="20%" align="center">
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<a accesskey="u" href="usingtxns.html">Up</a>
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</td>
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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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