1<!--$Id--> 2<!--Copyright (c) 1997,2008 Oracle. All rights reserved.--> 3<!--See the file LICENSE for redistribution information.--> 4<html> 5<head> 6<title>Berkeley DB: DB_ENV->log_set_config</title> 7<meta name="description" content="Berkeley DB: An embedded database programmatic toolkit."> 8<meta name="keywords" content="embedded,database,programmatic,toolkit,btree,hash,hashing,transaction,transactions,locking,logging,access method,access methods,Java,C,C++"> 9</head> 10<body bgcolor=white> 11<table width="100%"><tr valign=top> 12<td> 13<b>DB_ENV->log_set_config</b> 14</td> 15<td align=right> 16<a href="/api_c/api_core.html"><img src="/images/api.gif" alt="API"></a> 17<a href="/ref/toc.html"><img src="/images/ref.gif" alt="Ref"></a></td> 18</tr></table> 19<hr size=1 noshade> 20<tt> 21<b><pre> 22#include <db.h> 23<p> 24int 25DB_ENV->log_set_config(DB_ENV *dbenv, u_int32_t flags, int onoff); 26<p> 27int 28DB_ENV->log_get_config(DB_ENV *dbenv, u_int32_t which, int *onoffp); 29</pre></b> 30<hr size=1 noshade> 31<b>Description: DB_ENV->log_set_config</b> 32<p>The DB_ENV->log_set_config method configures the Berkeley DB logging 33subsystem.</p> 34<p>The DB_ENV->log_set_config method configures a database environment, not only operations 35performed using the specified <a href="/api_c/env_class.html">DB_ENV</a> handle.</p> 36<p>The DB_ENV->log_set_config method may be called at any time during the life of the 37application.</p> 38<p>The DB_ENV->log_set_config method 39returns a non-zero error value on failure 40and 0 on success. 41</p> 42<b>Parameters</b> <br> 43 <b>flags</b><ul compact><li>The <b>flags</b> parameter must be set by bitwise inclusively <b>OR</b>'ing together one or more 44of the following values: 45<br> 46<a name="2"><!--meow--></a> 47<b><a name="DB_LOG_DIRECT">DB_LOG_DIRECT</a></b><ul compact><li>Turn off system buffering of Berkeley DB log files to avoid double caching. 48<p>Calling DB_ENV->log_set_config with the DB_LOG_DIRECT flag only affects 49the specified <a href="/api_c/env_class.html">DB_ENV</a> handle (and any other Berkeley DB handles opened 50within the scope of that handle). 51For consistent behavior across the environment, all <a href="/api_c/env_class.html">DB_ENV</a> 52handles opened in the environment must either set the DB_LOG_DIRECT flag 53or the flag should be specified in the <a href="/ref/env/db_config.html#DB_CONFIG">DB_CONFIG</a> configuration 54file.</p> 55<p>The DB_LOG_DIRECT flag may be used to configure Berkeley DB at any time during 56the life of the application.</p></ul> 57<a name="3"><!--meow--></a> 58<b><a name="DB_LOG_DSYNC">DB_LOG_DSYNC</a></b><ul compact><li>Configure Berkeley DB to flush log writes to the backing disk before returning 59from the write system call, rather than flushing log writes explicitly 60in a separate system call, as necessary. This is only available on some 61systems (for example, systems supporting the IEEE/ANSI Std 1003.1 (POSIX) standard 62O_DSYNC flag, or systems supporting the Windows FILE_FLAG_WRITE_THROUGH 63flag). This flag may result in inaccurate file modification times and 64other file-level information for Berkeley DB log files. This flag may offer 65a performance increase on some systems and a performance decrease on 66others. 67<p>Calling DB_ENV->log_set_config with the DB_LOG_DSYNC flag only affects 68the specified <a href="/api_c/env_class.html">DB_ENV</a> handle (and any other Berkeley DB handles opened 69within the scope of that handle). 70For consistent behavior across the environment, all <a href="/api_c/env_class.html">DB_ENV</a> 71handles opened in the environment must either set the DB_LOG_DSYNC flag 72or the flag should be specified in the <a href="/ref/env/db_config.html#DB_CONFIG">DB_CONFIG</a> configuration 73file.</p> 74<p>The DB_LOG_DSYNC flag may be used to configure Berkeley DB at any time during 75the life of the application.</p></ul> 76<a name="4"><!--meow--></a> 77<b><a name="DB_LOG_AUTO_REMOVE">DB_LOG_AUTO_REMOVE</a></b><ul compact><li>If set, Berkeley DB will automatically remove log files that are no longer 78needed. 79<p>Automatic log file removal is likely to make catastrophic recovery 80impossible.</p> 81<p>Replication applications will rarely want to configure automatic log 82file removal as it increases the likelihood a master will be unable to 83satisfy a client's request for a recent log record.</p> 84<p>Calling DB_ENV->log_set_config with the DB_LOG_AUTO_REMOVE flag affects the 85database environment, including all threads of control accessing the 86database environment.</p> 87<p>The DB_LOG_AUTO_REMOVE flag may be used to configure Berkeley DB at any time during 88the life of the application.</p></ul> 89<a name="5"><!--meow--></a> 90<b><a name="DB_LOG_IN_MEMORY">DB_LOG_IN_MEMORY</a></b><ul compact><li>If set, maintain transaction logs in memory rather than on disk. This 91means that transactions exhibit the ACI (atomicity, consistency, and 92isolation) properties, but not D (durability); that is, database 93integrity will be maintained, but if the application or system fails, 94integrity will not persist. All database files must be verified and/or 95restored from a replication group master or archival backup after 96application or system failure. 97<p>When in-memory logs are configured and no more log buffer space is 98available, Berkeley DB methods may return an additional error value, 99<a name="DB_LOG_BUFFER_FULL">DB_LOG_BUFFER_FULL</a>. When choosing log buffer and file sizes 100for in-memory logs, applications should ensure the in-memory log buffer 101size is large enough that no transaction will ever span the entire 102buffer, and avoid a state where the in-memory buffer is full and no 103space can be freed because a transaction that started in the first log 104"file" is still active.</p> 105<p>Calling DB_ENV->log_set_config with the DB_LOG_IN_MEMORY flag affects the 106database environment, including all threads of control accessing the 107database environment.</p> 108<p>The DB_LOG_IN_MEMORY flag may be used to configure Berkeley DB only before the 109<a href="/api_c/env_open.html">DB_ENV->open</a> method is called.</p></ul> 110<a name="6"><!--meow--></a> 111<b><a name="DB_LOG_ZERO">DB_LOG_ZERO</a></b><ul compact><li>If set, zero all pages of a log file when that log file is created. This 112has shown to provide greater transaction throughput in some environments. 113The log file will be zeroed by the thread which needs to re-create the new log 114file. Other threads may not write to the log file while this is happening. 115<p>Calling DB_ENV->log_set_config with the DB_LOG_ZERO flag affects the 116database environment, including all threads of control accessing the 117database environment.</p> 118<p>The DB_LOG_ZERO flag may be used to configure Berkeley DB only before the 119<a href="/api_c/env_open.html">DB_ENV->open</a> method is called.</p></ul> 120<br></ul> 121 <b>onoff</b><ul compact><li>If the <b>onoff</b> parameter is zero, the specified flags are cleared; 122otherwise they are set.</ul> 123<br> 124<br><b>Errors</b> 125<p>The DB_ENV->log_set_config method 126may fail and return one of the following non-zero errors:</p> 127<br> 128<b>EINVAL</b><ul compact><li>An 129invalid flag value or parameter was specified.</ul> 130<br> 131<hr size=1 noshade> 132<b>Description: DB_ENV->log_get_config</b> 133<p>The DB_ENV->log_get_config method returns whether the specified <b>which</b> 134parameter is currently set or not.</p> 135<p>The DB_ENV->log_get_config method may be called at any time during the life of the 136application.</p> 137<p>The DB_ENV->log_get_config method 138returns a non-zero error value on failure 139and 0 on success. 140</p> 141<b>Parameters</b> <br> 142 <b>which</b><ul compact><li>The <b>which</b> parameter is the message value for which configuration 143is being checked.</ul> 144 <b>onoffp</b><ul compact><li>The <b>onoffp</b> parameter references memory into which 145 the configuration of the specified <b>which</b> parameter is copied.</ul> If the returned <b>onoff</b> value is zero, the parameter is off; 146otherwise on. 147<br> 148<hr size=1 noshade> 149<br><b>Class</b> 150<a href="/api_c/env_class.html">DB_ENV</a> 151<br><b>See Also</b> 152<a href="/api_c/env_list.html">Database Environments and Related Methods</a> 153</tt> 154<table width="100%"><tr><td><br></td><td align=right> 155<a href="/api_c/api_core.html"><img src="/images/api.gif" alt="API"></a><a href="/ref/toc.html"><img src="/images/ref.gif" alt="Ref"></a> 156</td></tr></table> 157<p><font size=1>Copyright (c) 1996,2008 Oracle. 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