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->set_flags</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->set_flags</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->set_flags(DB_ENV *dbenv, u_int32_t flags, int onoff); 26<p> 27int 28DB_ENV->get_flags(DB_ENV *dbenv, u_int32_t *flagsp); 29</pre></b> 30<hr size=1 noshade> 31<b>Description: DB_ENV->set_flags</b> 32<p>Configure a database environment.</p> 33<p>The database environment's flag values may also be configured using the 34environment's <a href="../ref/env/db_config.html#DB_CONFIG">DB_CONFIG</a> file. The syntax of the entry in that 35file is a single line with the string "set_flags", one or more whitespace 36characters, and the method flag parameter as a string; for example, "set_flags 37DB_TXN_NOSYNC". 38Because the <a href="../ref/env/db_config.html#DB_CONFIG">DB_CONFIG</a> file is read when the database environment 39is opened, it will silently overrule configuration done before that 40time.</p> 41<p>The DB_ENV->set_flags method 42returns a non-zero error value on failure 43and 0 on success. 44</p> 45<b>Parameters</b> <br> 46 <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 47of the following values: 48<br> 49<b><a name="DB_AUTO_COMMIT">DB_AUTO_COMMIT</a></b><ul compact><li>If set, <a href="../api_c/db_class.html">DB</a> handle operations for which no explicit transaction 50handle was specified, and which modify databases in the database 51environment, will be automatically enclosed within a transaction. 52<p>Calling DB_ENV->set_flags with the <a href="../api_c/env_set_flags.html#DB_AUTO_COMMIT">DB_AUTO_COMMIT</a> flag only affects 53the specified <a href="../api_c/env_class.html">DB_ENV</a> handle (and any other Berkeley DB handles opened 54within the scope of that handle). 55For consistent behavior across the environment, all <a href="../api_c/env_class.html">DB_ENV</a> 56handles opened in the environment must either set the <a href="../api_c/env_set_flags.html#DB_AUTO_COMMIT">DB_AUTO_COMMIT</a> flag 57or the flag should be specified in the <a href="../ref/env/db_config.html#DB_CONFIG">DB_CONFIG</a> configuration 58file.</p> 59<p>The <a href="../api_c/env_set_flags.html#DB_AUTO_COMMIT">DB_AUTO_COMMIT</a> flag may be used to configure Berkeley DB at any time during 60the life of the application.</p></ul> 61<a name="2"><!--meow--></a> 62<b><a name="DB_CDB_ALLDB">DB_CDB_ALLDB</a></b><ul compact><li>If set, Berkeley DB Concurrent Data Store applications will perform locking on an environment-wide 63basis rather than on a per-database basis. 64<p>Calling DB_ENV->set_flags with the DB_CDB_ALLDB flag only affects 65the specified <a href="../api_c/env_class.html">DB_ENV</a> handle (and any other Berkeley DB handles opened 66within the scope of that handle). 67For consistent behavior across the environment, all <a href="../api_c/env_class.html">DB_ENV</a> 68handles opened in the environment must either set the DB_CDB_ALLDB flag 69or the flag should be specified in the <a href="../ref/env/db_config.html#DB_CONFIG">DB_CONFIG</a> configuration 70file.</p> 71<p>The DB_CDB_ALLDB flag may be used to configure Berkeley DB only before the 72<a href="../api_c/env_open.html">DB_ENV->open</a> method is called.</p></ul> 73<a name="3"><!--meow--></a> 74<b><a name="DB_DIRECT_DB">DB_DIRECT_DB</a></b><ul compact><li>Turn off system buffering of Berkeley DB database files to avoid double caching. 75<p>Calling DB_ENV->set_flags with the DB_DIRECT_DB flag only affects 76the specified <a href="../api_c/env_class.html">DB_ENV</a> handle (and any other Berkeley DB handles opened 77within the scope of that handle). 78For consistent behavior across the environment, all <a href="../api_c/env_class.html">DB_ENV</a> 79handles opened in the environment must either set the DB_DIRECT_DB flag 80or the flag should be specified in the <a href="../ref/env/db_config.html#DB_CONFIG">DB_CONFIG</a> configuration 81file.</p> 82<p>The DB_DIRECT_DB flag may be used to configure Berkeley DB at any time during 83the life of the application.</p></ul> 84<a name="4"><!--meow--></a> 85<b><a name="DB_DSYNC_DB">DB_DSYNC_DB</a></b><ul compact><li>Configure Berkeley DB to flush database writes to the backing disk before 86returning from the write system call, rather than flushing database 87writes explicitly in a separate system call, as necessary. This is only 88available on some systems (for example, systems supporting the 89IEEE/ANSI Std 1003.1 (POSIX) standard O_DSYNC flag, or systems supporting the Windows 90FILE_FLAG_WRITE_THROUGH flag). This flag may result in inaccurate file 91modification times and other file-level information for Berkeley DB database 92files. This flag will almost certainly result in a performance decrease 93on most systems. This flag is only applicable to certain filesysystem 94(for example, the Veritas VxFS filesystem), where the filesystem's 95support for trickling writes back to stable storage behaves badly (or 96more likely, has been misconfigured). 97<p>Calling DB_ENV->set_flags with the DB_DSYNC_DB flag only affects 98the specified <a href="../api_c/env_class.html">DB_ENV</a> handle (and any other Berkeley DB handles opened 99within the scope of that handle). 100For consistent behavior across the environment, all <a href="../api_c/env_class.html">DB_ENV</a> 101handles opened in the environment must either set the DB_DSYNC_DB flag 102or the flag should be specified in the <a href="../ref/env/db_config.html#DB_CONFIG">DB_CONFIG</a> configuration 103file.</p> 104<p>The DB_DSYNC_DB flag may be used to configure Berkeley DB at any time during 105the life of the application.</p></ul> 106<b><a name="DB_MULTIVERSION">DB_MULTIVERSION</a></b><ul compact><li>If set, all databases in the environment will be opened as if 107DB_MULTIVERSION is passed to <a href="../api_c/db_open.html">DB->open</a>. This flag will 108be ignored for queue databases for which DB_MULTIVERSION is not 109supported. 110<p>Calling DB_ENV->set_flags with the DB_MULTIVERSION flag only affects 111the specified <a href="../api_c/env_class.html">DB_ENV</a> handle (and any other Berkeley DB handles opened 112within the scope of that handle). 113For consistent behavior across the environment, all <a href="../api_c/env_class.html">DB_ENV</a> 114handles opened in the environment must either set the DB_MULTIVERSION flag 115or the flag should be specified in the <a href="../ref/env/db_config.html#DB_CONFIG">DB_CONFIG</a> configuration 116file.</p> 117<p>The DB_MULTIVERSION flag may be used to configure Berkeley DB at any time during 118the life of the application.</p></ul> 119<a name="5"><!--meow--></a> 120<b><a name="DB_NOLOCKING">DB_NOLOCKING</a></b><ul compact><li>If set, Berkeley DB will grant all requested mutual exclusion mutexes and 121database locks without regard for their actual availability. This 122functionality should never be used for purposes other than debugging. 123<p>Calling DB_ENV->set_flags with the DB_NOLOCKING flag only affects 124the specified <a href="../api_c/env_class.html">DB_ENV</a> handle (and any other Berkeley DB handles opened 125within the scope of that handle). 126</p> 127<p>The DB_NOLOCKING flag may be used to configure Berkeley DB at any time during 128the life of the application.</p></ul> 129<a name="6"><!--meow--></a> 130<b><a name="DB_NOMMAP">DB_NOMMAP</a></b><ul compact><li>If set, Berkeley DB will copy read-only database files into the local cache 131instead of potentially mapping them into process memory (see the 132description of the <a href="../api_c/env_set_mp_mmapsize.html">DB_ENV->set_mp_mmapsize</a> method for further 133information). 134<p>Calling DB_ENV->set_flags with the DB_NOMMAP flag only affects 135the specified <a href="../api_c/env_class.html">DB_ENV</a> handle (and any other Berkeley DB handles opened 136within the scope of that handle). 137For consistent behavior across the environment, all <a href="../api_c/env_class.html">DB_ENV</a> 138handles opened in the environment must either set the DB_NOMMAP flag 139or the flag should be specified in the <a href="../ref/env/db_config.html#DB_CONFIG">DB_CONFIG</a> configuration 140file.</p> 141<p>The DB_NOMMAP flag may be used to configure Berkeley DB at any time during 142the life of the application.</p></ul> 143<a name="7"><!--meow--></a> 144<b><a name="DB_NOPANIC">DB_NOPANIC</a></b><ul compact><li>If set, Berkeley DB will ignore any panic state in the database environment. 145(Database environments in a panic state normally refuse all attempts to 146call Berkeley DB functions, returning <a href="../ref/program/errorret.html#DB_RUNRECOVERY">DB_RUNRECOVERY</a>.) This 147functionality should never be used for purposes other than debugging. 148<p>Calling DB_ENV->set_flags with the DB_NOPANIC flag only affects 149the specified <a href="../api_c/env_class.html">DB_ENV</a> handle (and any other Berkeley DB handles opened 150within the scope of that handle). 151</p> 152<p>The DB_NOPANIC flag may be used to configure Berkeley DB at any time during 153the life of the application.</p></ul> 154<b><a name="DB_OVERWRITE">DB_OVERWRITE</a></b><ul compact><li>Overwrite files stored in encrypted formats before deleting them. Berkeley DB 155overwrites files using alternating 0xff, 0x00 and 0xff byte patterns. 156For file overwriting to be effective, the underlying file must be stored 157on a fixed-block filesystem. Systems with journaling or logging filesystems 158will require operating system support and probably modification of the 159Berkeley DB sources. 160<p>Calling DB_ENV->set_flags with the DB_OVERWRITE flag only affects 161the specified <a href="../api_c/env_class.html">DB_ENV</a> handle (and any other Berkeley DB handles opened 162within the scope of that handle). 163</p> 164<p>The DB_OVERWRITE flag may be used to configure Berkeley DB at any time during 165the life of the application.</p></ul> 166<a name="8"><!--meow--></a> 167<b><a name="DB_PANIC_ENVIRONMENT">DB_PANIC_ENVIRONMENT</a></b><ul compact><li>If set, Berkeley DB will set the panic state for the database environment. 168(Database environments in a panic state normally refuse all attempts to 169call Berkeley DB functions, returning <a href="../ref/program/errorret.html#DB_RUNRECOVERY">DB_RUNRECOVERY</a>.) This flag may 170not be specified using the environment's <a href="../ref/env/db_config.html#DB_CONFIG">DB_CONFIG</a> file. 171<p>Calling DB_ENV->set_flags with the DB_PANIC_ENVIRONMENT flag affects the 172database environment, including all threads of control accessing the 173database environment.</p> 174<p>The DB_PANIC_ENVIRONMENT flag may be used to configure Berkeley DB only after the 175<a href="../api_c/env_open.html">DB_ENV->open</a> method is called.</p></ul> 176<a name="9"><!--meow--></a> 177<b><a name="DB_REGION_INIT">DB_REGION_INIT</a></b><ul compact><li>In some applications, the expense of page-faulting the underlying shared 178memory regions can affect performance. (For example, if the page-fault 179occurs while holding a lock, other lock requests can convoy, and overall 180throughput may decrease.) If set, Berkeley DB will page-fault shared regions 181into memory when initially creating or joining a Berkeley DB environment. In 182addition, Berkeley DB will write the shared regions when creating an 183environment, forcing the underlying virtual memory and filesystems to 184instantiate both the necessary memory and the necessary disk space. 185This can also avoid out-of-disk space failures later on. 186<p>Calling DB_ENV->set_flags with the DB_REGION_INIT flag only affects 187the specified <a href="../api_c/env_class.html">DB_ENV</a> handle (and any other Berkeley DB handles opened 188within the scope of that handle). 189For consistent behavior across the environment, all <a href="../api_c/env_class.html">DB_ENV</a> 190handles opened in the environment must either set the DB_REGION_INIT flag 191or the flag should be specified in the <a href="../ref/env/db_config.html#DB_CONFIG">DB_CONFIG</a> configuration 192file.</p> 193<p>The DB_REGION_INIT flag may be used to configure Berkeley DB at any time during 194the life of the application.</p></ul> 195<b><a name="DB_TIME_NOTGRANTED">DB_TIME_NOTGRANTED</a></b><ul compact><li>If set, database calls timing out based on lock or transaction timeout 196values will 197return <a href="../ref/program/errorret.html#DB_LOCK_NOTGRANTED">DB_LOCK_NOTGRANTED</a> instead of <a href="../ref/program/errorret.html#DB_LOCK_DEADLOCK">DB_LOCK_DEADLOCK</a>. 198This allows applications to distinguish between operations which have 199deadlocked and operations which have exceeded their time limits. 200<p>Calling DB_ENV->set_flags with the DB_TIME_NOTGRANTED flag only affects 201the specified <a href="../api_c/env_class.html">DB_ENV</a> handle (and any other Berkeley DB handles opened 202within the scope of that handle). 203For consistent behavior across the environment, all <a href="../api_c/env_class.html">DB_ENV</a> 204handles opened in the environment must either set the DB_TIME_NOTGRANTED flag 205or the flag should be specified in the <a href="../ref/env/db_config.html#DB_CONFIG">DB_CONFIG</a> configuration 206file.</p> 207<p>The DB_TIME_NOTGRANTED flag may be used to configure Berkeley DB at any time during 208the life of the application.</p></ul> 209<a name="10"><!--meow--></a> 210<b><a name="DB_TXN_NOSYNC">DB_TXN_NOSYNC</a></b><ul compact><li>If set, Berkeley DB will not write or synchronously flush the log on transaction 211commit. 212This means that transactions exhibit the ACI (atomicity, consistency, 213and isolation) properties, but not D (durability); that is, database 214integrity will be maintained, but if the application or system fails, 215it is possible some number of the most recently committed transactions 216may be undone during recovery. The number of transactions at risk is 217governed by how many log updates can fit into the log buffer, how often 218the operating system flushes dirty buffers to disk, and how often the 219log is checkpointed. 220<p>Calling DB_ENV->set_flags with the DB_TXN_NOSYNC flag only affects 221the specified <a href="../api_c/env_class.html">DB_ENV</a> handle (and any other Berkeley DB handles opened 222within the scope of that handle). 223For consistent behavior across the environment, all <a href="../api_c/env_class.html">DB_ENV</a> 224handles opened in the environment must either set the DB_TXN_NOSYNC flag 225or the flag should be specified in the <a href="../ref/env/db_config.html#DB_CONFIG">DB_CONFIG</a> configuration 226file.</p> <p>The DB_TXN_NOSYNC flag may be used to configure Berkeley DB at any time during 227the life of the application.</p></ul> 228<b><a name="DB_TXN_NOWAIT">DB_TXN_NOWAIT</a></b><ul compact><li>If set and a lock is unavailable for any Berkeley DB operation performed in 229the context of a transaction, cause the operation to 230return <a href="../ref/program/errorret.html#DB_LOCK_DEADLOCK">DB_LOCK_DEADLOCK</a> (or <a href="../ref/program/errorret.html#DB_LOCK_NOTGRANTED">DB_LOCK_NOTGRANTED</a> if 231configured using the DB_TIME_NOTGRANTED flag). 232<p>Calling DB_ENV->set_flags with the DB_TXN_NOWAIT flag only affects 233the specified <a href="../api_c/env_class.html">DB_ENV</a> handle (and any other Berkeley DB handles opened 234within the scope of that handle). 235For consistent behavior across the environment, all <a href="../api_c/env_class.html">DB_ENV</a> 236handles opened in the environment must either set the DB_TXN_NOWAIT flag 237or the flag should be specified in the <a href="../ref/env/db_config.html#DB_CONFIG">DB_CONFIG</a> configuration 238file.</p> 239<p>The DB_TXN_NOWAIT flag may be used to configure Berkeley DB at any time during 240the life of the application.</p></ul> 241<b><a name="DB_TXN_SNAPSHOT">DB_TXN_SNAPSHOT</a></b><ul compact><li>If set, all transactions in the environment will be started as if 242DB_TXN_SNAPSHOT were passed to <a href="../api_c/txn_begin.html">DB_ENV->txn_begin</a>, and all 243non-transactional cursors will be opened as if DB_TXN_SNAPSHOT 244were passed to <a href="../api_c/db_cursor.html">DB->cursor</a>. 245<p>Calling DB_ENV->set_flags with the DB_TXN_SNAPSHOT flag only affects 246the specified <a href="../api_c/env_class.html">DB_ENV</a> handle (and any other Berkeley DB handles opened 247within the scope of that handle). 248For consistent behavior across the environment, all <a href="../api_c/env_class.html">DB_ENV</a> 249handles opened in the environment must either set the DB_TXN_SNAPSHOT flag 250or the flag should be specified in the <a href="../ref/env/db_config.html#DB_CONFIG">DB_CONFIG</a> configuration 251file.</p> 252<p>The DB_TXN_SNAPSHOT flag may be used to configure Berkeley DB at any time during 253the life of the application.</p></ul> 254<a name="11"><!--meow--></a> 255<b><a name="DB_TXN_WRITE_NOSYNC">DB_TXN_WRITE_NOSYNC</a></b><ul compact><li>If set, Berkeley DB will write, but will not synchronously flush, the log on 256transaction commit. 257This means that transactions exhibit the ACI (atomicity, consistency, 258and isolation) properties, but not D (durability); that is, database 259integrity will be maintained, but if the system fails, it is possible 260some number of the most recently committed transactions may be undone 261during recovery. The number of transactions at risk is governed by how 262often the system flushes dirty buffers to disk and how often the log is 263checkpointed. 264<p>Calling DB_ENV->set_flags with the DB_TXN_WRITE_NOSYNC flag only affects 265the specified <a href="../api_c/env_class.html">DB_ENV</a> handle (and any other Berkeley DB handles opened 266within the scope of that handle). 267For consistent behavior across the environment, all <a href="../api_c/env_class.html">DB_ENV</a> 268handles opened in the environment must either set the DB_TXN_WRITE_NOSYNC flag 269or the flag should be specified in the <a href="../ref/env/db_config.html#DB_CONFIG">DB_CONFIG</a> configuration 270file.</p> 271<p>The DB_TXN_WRITE_NOSYNC flag may be used to configure Berkeley DB at any time during 272the life of the application.</p></ul> 273<a name="12"><!--meow--></a> 274<b><a name="DB_YIELDCPU">DB_YIELDCPU</a></b><ul compact><li>If set, Berkeley DB will yield the processor immediately after each page or 275mutex acquisition. This functionality should never be used for purposes 276other than stress testing. 277<p>Calling DB_ENV->set_flags with the DB_YIELDCPU flag only affects 278the specified <a href="../api_c/env_class.html">DB_ENV</a> handle (and any other Berkeley DB handles opened 279within the scope of that handle). 280For consistent behavior across the environment, all <a href="../api_c/env_class.html">DB_ENV</a> 281handles opened in the environment must either set the DB_YIELDCPU flag 282or the flag should be specified in the <a href="../ref/env/db_config.html#DB_CONFIG">DB_CONFIG</a> configuration 283file.</p> 284<p>The DB_YIELDCPU flag may be used to configure Berkeley DB at any time during 285the life of the application.</p></ul> 286<br></ul> 287 <b>onoff</b><ul compact><li>If the <b>onoff</b> parameter is zero, the specified flags are cleared; 288otherwise they are set.</ul> 289<br> 290<br><b>Errors</b> 291<p>The DB_ENV->set_flags method 292may fail and return one of the following non-zero errors:</p> 293<br> 294<b>EINVAL</b><ul compact><li>An 295invalid flag value or parameter was specified.</ul> 296<br> 297<hr size=1 noshade> 298<b>Description: DB_ENV->get_flags</b> 299<p>The DB_ENV->get_flags method returns the configuration flags.</p> 300<p>The DB_ENV->get_flags method may be called at any time during the life of the 301application.</p> 302<p>The DB_ENV->get_flags method 303returns a non-zero error value on failure 304and 0 on success. 305</p> 306<b>Parameters</b> <br> 307 <b>flagsp</b><ul compact><li>The DB_ENV->get_flags method returns the 308configuration flags in <b>flagsp</b>.</ul> 309<br> 310<hr size=1 noshade> 311<br><b>Class</b> 312<a href="../api_c/env_class.html">DB_ENV</a> 313<br><b>See Also</b> 314<a href="../api_c/env_list.html">Database Environments and Related Methods</a> 315</tt> 316<table width="100%"><tr><td><br></td><td align=right> 317<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> 318</td></tr></table> 319<p><font size=1>Copyright (c) 1996,2008 Oracle. All rights reserved.</font> 320</body> 321</html> 322
