<?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">DB_ENV->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 <stdio.h> #include <stdlib.h> #include "db.h" int main(void) { int ret, ret_c; u_int32_t db_flags, env_flags; DB *dbp; DB_ENV *envp; DBT key, data; const char *db_home_dir = "/tmp/myEnvironment"; const char *file_name = "mydb.db"; const char *keystr ="thekey"; const char *datastr = "thedata"; dbp = NULL; envp = NULL; /* Open the environment */ ret = db_env_create(&envp, 0); if (ret != 0) { fprintf(stderr, "Error creating environment handle: %s\n", db_strerror(ret)); return (EXIT_FAILURE); } env_flags = DB_CREATE | /* Create the environment if it does * not already exist. */ DB_INIT_TXN | /* Initialize transactions */ DB_INIT_LOCK | /* Initialize locking. */ DB_INIT_LOG | /* Initialize logging */ DB_INIT_MPOOL; /* Initialize the in-memory cache. */ ret = envp->open(envp, db_home_dir, env_flags, 0); if (ret != 0) { fprintf(stderr, "Error opening environment: %s\n", db_strerror(ret)); goto err; } /* Initialize the DB handle */ ret = db_create(&dbp, envp, 0); if (ret != 0) { envp->err(envp, ret, "Database creation failed"); goto err; } db_flags = DB_CREATE | DB_AUTO_COMMIT; /* * Open the database. Note that we are using auto commit for the open, * so the database is able to support transactions. */ ret = dbp->open(dbp, /* Pointer to the database */ 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 */ if (ret != 0) { envp->err(envp, ret, "Database '%s' open failed", file_name); goto err; } /* Prepare the DBTs */ memset(&key, 0, sizeof(DBT)); memset(&data, 0, sizeof(DBT)); key.data = &keystr; key.size = strlen(keystr) + 1; data.data = &datastr; data.size = strlen(datastr) + 1; /* * Perform the database write. A txn handle is not provided, but the * database support auto commit, so auto commit is used for the write. */ ret = dbp->put(dbp, NULL, &key, &data, 0); if (ret != 0) { envp->err(envp, ret, "Database put failed."); goto err; } err: /* Close the database */ if (dbp != NULL) { ret_c = dbp->close(dbp, 0); if (ret_c != 0) { envp->err(envp, ret_c, "Database close failed."); ret = ret_c } } /* Close the environment */ if (envp != NULL) { ret_c = envp->close(envp, 0); if (ret_c != 0) { fprintf(stderr, "environment close failed: %s\n", db_strerror(ret_c)); ret = ret_c; } } return (ret == 0 ? EXIT_SUCCESS : EXIT_FAILURE); } </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>