Import BSDDB 4.7.25 (as of svn r89086)
This commit is contained in:
Zachary Ware
155
docs/gsg_txn/C/txncursor.html
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155
docs/gsg_txn/C/txncursor.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 V1.62.4" />
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<link rel="home" 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="previous" 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 class="navheader">
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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></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 <stdio.h>
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#include <stdlib.h>
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#include "db.h"
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int
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main(void)
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{
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DBT key, data;
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DBC *cursorp;
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DB_TXN *txn = NULL;
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int ret, c_ret;
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char *replacementString = "new string";
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...
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/* environment and db handle creation omitted */
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...
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/* Get the txn handle */
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txn = NULL;
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ret = envp->txn_begin(envp, NULL, &txn, 0);
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if (ret != 0) {
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envp->err(envp, ret, "Transaction begin failed.");
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goto err;
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}
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/* Get the cursor, supply the txn handle at that time */
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ret = dbp->cursor(dbp, txn, &cursorp, 0);
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if (ret != 0) {
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envp->err(envp, ret, "Cursor open failed.");
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txn->abort(txn);
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goto err;
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}
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/*
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* Now use the cursor. Note that we do not supply any txn handles to these
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* methods.
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*/
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/* Prepare the DBTs */
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memset(&key, 0, sizeof(DBT));
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memset(&data, 0, sizeof(DBT));
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while (cursor->get(&key, &data, DB_NEXT) == 0) {
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data->data = (void *)replacementString;
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data->size = (strlen(replacementString) + 1) * sizeof(char);
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c_ret = cursor->put(cursor, &key, &data, DB_CURRENT);
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if (c_ret != 0) {
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/* abort the transaction and goto error */
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envp->err(envp, ret, "Cursor put failed.");
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cursorp->close(cursorp);
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cursorp = NULL;
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txn->abort(txn);
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goto err;
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}
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}
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/*
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* Commit the transaction. Note that the transaction handle
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* can no longer be used.
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*/
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ret = cursorp->close(cursorp);
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if (ret != 0) {
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envp->err(envp, ret, "Cursor close failed.");
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txn->abort(txn);
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goto err;
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}
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ret = txn->commit(txn, 0);
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if (ret != 0) {
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envp->err(envp, ret, "Transaction commit failed.");
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goto err;
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}
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err:
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/* Close the cursor (if the handle is not NULL)
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* and perform whatever other cleanup is required */
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/* Close the database */
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/* Close the environment */
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...
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if (c_ret != 0)
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ret = c_ret;
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return (ret == 0 ? EXIT_SUCCESS : EXIT_FAILURE);
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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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