1<?xml version="1.0" encoding="UTF-8" standalone="no"?> 2<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> 3<html xmlns="http://www.w3.org/1999/xhtml"> 4 <head> 5 <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /> 6 <title>Opening a Transactional Environment and 7 Database 8 9 10 </title> 11 <link rel="stylesheet" href="gettingStarted.css" type="text/css" /> 12 <meta name="generator" content="DocBook XSL Stylesheets V1.62.4" /> 13 <link rel="home" href="index.html" title="Getting Started with Berkeley DB Transaction Processing" /> 14 <link rel="up" href="enabletxn.html" title="Chapter��2.��Enabling Transactions" /> 15 <link rel="previous" href="enabletxn.html" title="Chapter��2.��Enabling Transactions" /> 16 <link rel="next" href="usingtxns.html" title="Chapter��3.��Transaction Basics" /> 17 </head> 18 <body> 19 <div class="navheader"> 20 <table width="100%" summary="Navigation header"> 21 <tr> 22 <th colspan="3" align="center">Opening a Transactional Environment and 23 Database 24 25 26 </th> 27 </tr> 28 <tr> 29 <td width="20%" align="left"><a accesskey="p" href="enabletxn.html">Prev</a>��</td> 30 <th width="60%" align="center">Chapter��2.��Enabling Transactions</th> 31 <td width="20%" align="right">��<a accesskey="n" href="usingtxns.html">Next</a></td> 32 </tr> 33 </table> 34 <hr /> 35 </div> 36 <div class="sect1" lang="en" xml:lang="en"> 37 <div class="titlepage"> 38 <div> 39 <div> 40 <h2 class="title" style="clear: both"><a id="envopen"></a>Opening a Transactional Environment and 41 <span>Database</span> 42 43 44 </h2> 45 </div> 46 </div> 47 <div></div> 48 </div> 49 <p> 50 To enable transactions for your environment, you must initialize the 51 transactional subsystem. Note that doing this also initializes the 52 logging subsystem. In addition, you must initialize the memory pool 53 (in-memory cache). Frequently, but not always, you will also 54 initialize the locking subsystem. 55 56 57 <span> 58 For example: 59 </span> 60 61 </p> 62 <pre class="programlisting">#include "db_cxx.h" 63 64... 65 66int main(void) 67{ 68 u_int32_t env_flags = DB_CREATE | // If the environment does not 69 // exist, create it. 70 DB_INIT_LOCK | // Initialize locking 71 DB_INIT_LOG | // Initialize logging 72 DB_INIT_MPOOL | // Initialize the cache 73 DB_INIT_TXN; // Initialize transactions 74 75 std::string envHome("/export1/testEnv"); 76 DbEnv myEnv(0); 77 78 try { 79 80 myEnv.open(envHome.c_str(), env_flags, 0); 81 82 } catch(DbException &e) { 83 std::cerr << "Error opening database environment: " 84 << envHome << std::endl; 85 std::cerr << e.what() << std::endl; 86 return (EXIT_FAILURE); 87 } 88 89 try { 90 myEnv.close(0); 91 } catch(DbException &e) { 92 std::cerr << "Error closing database environment: " 93 << envHome << std::endl; 94 std::cerr << e.what() << std::endl; 95 return (EXIT_FAILURE); 96 } 97 98 return (EXIT_SUCCESS); 99} </pre> 100 <p> 101 You then create and open your database(s) as you would for a non-transactional system. 102 <span> 103 The only difference is that you must pass the environment handle to 104 the 105 106 <span> 107 <tt class="methodname">DbEnv::open()</tt> method, 108 </span> 109 and you must open the database within a transaction. 110 Typically auto commit is used for this purpose. To do so, pass 111 <tt class="literal">DB_AUTO_COMMIT</tt> to the database open command. 112 Also, make sure you close all your databases before you close 113 your environment. 114 For example: 115 </span> 116 117 118 </p> 119 <pre class="programlisting">#include "db_cxx.h" 120 121... 122 123int main(void) 124{ 125 u_int32_t env_flags = DB_CREATE | // If the environment does not 126 // exist, create it. 127 DB_INIT_LOCK | // Initialize locking 128 DB_INIT_LOG | // Initialize logging 129 DB_INIT_MPOOL | // Initialize the cache 130 DB_INIT_TXN; // Initialize transactions 131 132 <b class="userinput"><tt>u_int32_t db_flags = DB_CREATE | DB_AUTO_COMMIT; 133 Db *dbp = NULL; 134 const char *file_name = "mydb.db";</tt></b> 135 136 std::string envHome("/export1/testEnv"); 137 DbEnv myEnv(0); 138 139 try { 140 141 myEnv.open(envHome.c_str(), env_flags, 0); 142 <b class="userinput"><tt>dbp = new Db(&myEnv, 0); 143 dbp->open(NULL, // Txn pointer 144 file_name, // File name 145 NULL, // Logical db name 146 DB_BTREE, // Database type (using btree) 147 db_flags, // Open flags 148 0); // File mode. Using defaults </tt></b> 149 150 } catch(DbException &e) { 151 std::cerr << "Error opening database and environment: " 152 << file_name << ", " 153 << envHome << std::endl; 154 std::cerr << e.what() << std::endl; 155 } 156 157 try { 158 <b class="userinput"><tt>dbp->close(0);</tt></b> 159 myEnv.close(0); 160 } catch(DbException &e) { 161 std::cerr << "Error closing database and environment: " 162 << file_name << ", " 163 << envHome << std::endl; 164 std::cerr << e.what() << std::endl; 165 return (EXIT_FAILURE); 166 } 167 168 return (EXIT_SUCCESS); 169} </pre> 170 <div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"> 171 <h3 class="title">Note</h3> 172 <p> 173 Never close a database that has active transactions. Make sure 174 all transactions are resolved (either committed or aborted) 175 before closing the database. 176 </p> 177 </div> 178 </div> 179 <div class="navfooter"> 180 <hr /> 181 <table width="100%" summary="Navigation footer"> 182 <tr> 183 <td width="40%" align="left"><a accesskey="p" href="enabletxn.html">Prev</a>��</td> 184 <td width="20%" align="center"> 185 <a accesskey="u" href="enabletxn.html">Up</a> 186 </td> 187 <td width="40%" align="right">��<a accesskey="n" href="usingtxns.html">Next</a></td> 188 </tr> 189 <tr> 190 <td width="40%" align="left" valign="top">Chapter��2.��Enabling Transactions��</td> 191 <td width="20%" align="center"> 192 <a accesskey="h" href="index.html">Home</a> 193 </td> 194 <td width="40%" align="right" valign="top">��Chapter��3.��Transaction Basics</td> 195 </tr> 196 </table> 197 </div> 198 </body> 199</html> 200