<?xml version="1.0" encoding="UTF-8" standalone="no"?> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"> <head> <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /> <title>Auto Commit</title> <link rel="stylesheet" href="gettingStarted.css" type="text/css" /> <meta name="generator" content="DocBook XSL Stylesheets V1.62.4" /> <link rel="home" href="index.html" title="Getting Started with Berkeley DB Transaction Processing" /> <link rel="up" href="usingtxns.html" title="Chapter 3. Transaction Basics" /> <link rel="previous" href="abortresults.html" title="Aborting a Transaction" /> <link rel="next" href="nestedtxn.html" title="Nested Transactions" /> </head> <body> <div class="navheader"> <table width="100%" summary="Navigation header"> <tr> <th colspan="3" align="center">Auto Commit</th> </tr> <tr> <td width="20%" align="left"><a accesskey="p" href="abortresults.html">Prev</a> </td> <th width="60%" align="center">Chapter 3. Transaction Basics</th> <td width="20%" align="right"> <a accesskey="n" href="nestedtxn.html">Next</a></td> </tr> </table> <hr /> </div> <div class="sect1" lang="en" xml:lang="en"> <div class="titlepage"> <div> <div> <h2 class="title" style="clear: both"><a id="autocommit"></a>Auto Commit</h2> </div> </div> <div></div> </div> <p> While transactions are frequently used to provide atomicity to multiple database operations, it is sometimes necessary to perform a single database operation under the control of a transaction. Rather than force you to obtain a transaction, perform the single write operation, and then either commit or abort the transaction, you can automatically group this sequence of events using <span class="emphasis"><em>auto commit</em></span>. </p> <p> To use auto commit: </p> <div class="orderedlist"> <ol type="1"> <li> <p> Open your environment and your databases so that they support transactions. See <a href="enabletxn.html">Enabling Transactions</a> for details. </p> <p> Note that frequently auto commit is used for the environment or database open. To use auto commit for either your environment or database open, specify <tt class="literal">DB_AUTO_COMMIT</tt> to the <tt class="methodname">DbEnv::set_flags()</tt> or <tt class="methodname">Db::open()</tt> method. If you specify auto commit for the environment open, then you do not need to also specify auto commit for the database open. </p> </li> <li> <p> Do not provide a transactional handle to the method that is performing the database write operation. </p> </li> </ol> </div> <p> Note that auto commit is not available for cursors. You must always open your cursor using a transaction if you want the cursor's operations to be transactional protected. See <a href="txncursor.html">Transactional Cursors</a> for details on using transactional cursors. </p> <p> For example, the following uses auto commit to perform the database write operation: </p> <pre class="programlisting">#include "db_cxx.h" ... int main(void) { u_int32_t env_flags = DB_CREATE | // If the environment does not // exist, create it. DB_INIT_LOCK | // Initialize locking DB_INIT_LOG | // Initialize logging DB_INIT_MPOOL | // Initialize the cache DB_INIT_TXN; // Initialize transactions u_int32_t db_flags = DB_CREATE | DB_AUTO_COMMIT; Db *dbp = NULL; const char *file_name = "mydb.db"; const char *keystr ="thekey"; const char *datastr = "thedata"; std::string envHome("/export1/testEnv"); DbEnv myEnv(0); try { myEnv.open(envHome.c_str(), env_flags, 0); dbp = new Db(&myEnv, 0); // Open the database. Note that we are using auto commit for // the open, so the database is able to support transactions. dbp->open(NULL, // Txn pointer file_name, // File name NULL, // Logical db name */ DB_BTREE, // Database type (using btree) db_flags, // Open flags 0); // File mode. Using defaults Dbt key, data; key.set_data(keystr); key.set_size((strlen(keystr) + 1) * sizeof(char)); key.set_data(datastr); key.set_size((strlen(datastr) + 1) * sizeof(char)); // Perform the write. Because the database was opened to support // auto commit, this write is performed using auto commit. db->put(NULL, &key, &data, 0); } catch(DbException &e) { std::cerr << "Error opening database and environment: " << file_name << ", " << envHome << std::endl; std::cerr << e.what() << std::endl; } try { if (dbp != NULL) dbp->close(0); myEnv.close(0); } catch(DbException &e) { std::cerr << "Error closing database and environment: " << file_name << ", " << envHome << std::endl; std::cerr << e.what() << std::endl; return (EXIT_FAILURE); } return (EXIT_SUCCESS); } </pre> </div> <div class="navfooter"> <hr /> <table width="100%" summary="Navigation footer"> <tr> <td width="40%" align="left"><a accesskey="p" href="abortresults.html">Prev</a> </td> <td width="20%" align="center"> <a accesskey="u" href="usingtxns.html">Up</a> </td> <td width="40%" align="right"> <a accesskey="n" href="nestedtxn.html">Next</a></td> </tr> <tr> <td width="40%" align="left" valign="top">Aborting a Transaction </td> <td width="20%" align="center"> <a accesskey="h" href="index.html">Home</a> </td> <td width="40%" align="right" valign="top"> Nested Transactions</td> </tr> </table> </div> </body> </html>