Berkeley DB: DbEnv::set_flags
Description: Berkeley DB: An embedded database programmatic toolkit.
Keywords: embedded,database,programmatic,toolkit,btree,hash,hashing,transaction,transactions,locking,logging,access method,access methods,Java,C,C++

### DbEnv::set_flags |

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    #include <db_cxx.h>

    int
    DbEnv::set_flags(u_int32_t flags, int onoff);

    int
    DbEnv::get_flags(u_int32_t *flagsp)

### Description: DbEnv::set_flags

Configure a database environment.

The database environment's flag values may also be configured using the environment's DB_CONFIG file. The syntax of the entry in that file is a single line with the string "set_flags", one or more whitespace characters, and the method flag parameter as a string; for example, "set_flags DB_TXN_NOSYNC". Because the DB_CONFIG file is read when the database environment is opened, it will silently overrule configuration done before that time.

The DbEnv::set_flags method either returns a non-zero error value or throws an exception that encapsulates a non-zero error value on failure, and returns 0 on success.

### Parameters

flags
  The flags parameter must be set by bitwise inclusively OR'ing together one or more of the following values:
  DB_AUTO_COMMIT
    If set, Db handle operations for which no explicit transaction handle was specified, and which modify databases in the database environment, will be automatically enclosed within a transaction.

    Calling DbEnv::set_flags with the DB_AUTO_COMMIT flag only affects the specified DbEnv handle (and any other Berkeley DB handles opened within the scope of that handle). For consistent behavior across the environment, all DbEnv handles opened in the environment must either set the DB_AUTO_COMMIT flag or the flag should be specified in the DB_CONFIG configuration file.

    The DB_AUTO_COMMIT flag may be used to configure Berkeley DB at any time during the life of the application.

  DB_CDB_ALLDB
    If set, Berkeley DB Concurrent Data Store applications will perform locking on an environment-wide basis rather than on a per-database basis.

    Calling DbEnv::set_flags with the DB_CDB_ALLDB flag only affects the specified DbEnv handle (and any other Berkeley DB handles opened within the scope of that handle). For consistent behavior across the environment, all DbEnv handles opened in the environment must either set the DB_CDB_ALLDB flag or the flag should be specified in the DB_CONFIG configuration file.

    The DB_CDB_ALLDB flag may be used to configure Berkeley DB only before the DbEnv::open method is called.

  DB_DIRECT_DB
    Turn off system buffering of Berkeley DB database files to avoid double caching.

    Calling DbEnv::set_flags with the DB_DIRECT_DB flag only affects the specified DbEnv handle (and any other Berkeley DB handles opened within the scope of that handle). For consistent behavior across the environment, all DbEnv handles opened in the environment must either set the DB_DIRECT_DB flag or the flag should be specified in the DB_CONFIG configuration file.

    The DB_DIRECT_DB flag may be used to configure Berkeley DB at any time during the life of the application.

  DB_DIRECT_LOG
    Turn off system buffering of Berkeley DB log files to avoid double caching.

    Calling DbEnv::set_flags with the DB_DIRECT_LOG flag only affects the specified DbEnv handle (and any other Berkeley DB handles opened within the scope of that handle). For consistent behavior across the environment, all DbEnv handles opened in the environment must either set the DB_DIRECT_LOG flag or the flag should be specified in the DB_CONFIG configuration file.

    The DB_DIRECT_LOG flag may be used to configure Berkeley DB at any time during the life of the application.

  DB_DSYNC_DB
    Configure Berkeley DB to flush database writes to the backing disk before returning from the write system call, rather than flushing database writes explicitly in a separate system call, as necessary. This is only available on some systems (for example, systems supporting the IEEE/ANSI Std 1003.1 (POSIX) standard O_DSYNC flag, or systems supporting the Windows FILE_FLAG_WRITE_THROUGH flag). This flag may result in inaccurate file modification times and other file-level information for Berkeley DB database files. This flag will almost certainly result in a performance decrease on most systems. This flag is only applicable to certain filesysystem (for example, the Veritas VxFS filesystem), where the filesystem's support for trickling writes back to stable storage behaves badly (or more likely, has been misconfigured).

    Calling DbEnv::set_flags with the DB_DSYNC_DB flag only affects the specified DbEnv handle (and any other Berkeley DB handles opened within the scope of that handle). For consistent behavior across the environment, all DbEnv handles opened in the environment must either set the DB_DSYNC_DB flag or the flag should be specified in the DB_CONFIG configuration file.

    The DB_DSYNC_DB flag may be used to configure Berkeley DB at any time during the life of the application.

  DB_DSYNC_LOG
    Configure Berkeley DB to flush log writes to the backing disk before returning from the write system call, rather than flushing log writes explicitly in a separate system call, as necessary. This is only available on some systems (for example, systems supporting the IEEE/ANSI Std 1003.1 (POSIX) standard O_DSYNC flag, or systems supporting the Windows FILE_FLAG_WRITE_THROUGH flag). This flag may result in inaccurate file modification times and other file-level information for Berkeley DB log files. This flag may offer a performance increase on some systems and a performance decrease on others.

    Calling DbEnv::set_flags with the DB_DSYNC_LOG flag only affects the specified DbEnv handle (and any other Berkeley DB handles opened within the scope of that handle). For consistent behavior across the environment, all DbEnv handles opened in the environment must either set the DB_DSYNC_LOG flag or the flag should be specified in the DB_CONFIG configuration file.

    The DB_DSYNC_LOG flag may be used to configure Berkeley DB at any time during the life of the application.

  DB_LOG_AUTOREMOVE
    If set, Berkeley DB will automatically remove log files that are no longer needed. Automatic log file removal is likely to make catastrophic recovery impossible.

    Calling DbEnv::set_flags with the DB_LOG_AUTOREMOVE flag affects the database environment, including all threads of control accessing the database environment.

    The DB_LOG_AUTOREMOVE flag may be used to configure Berkeley DB at any time during the life of the application.

  DB_LOG_INMEMORY
    If set, maintain transaction logs in memory rather than on disk. This means that transactions exhibit the ACI (atomicity, consistency, and isolation) properties, but not D (durability); that is, database integrity will be maintained, but if the application or system fails, integrity will not persist. All database files must be verified and/or restored from a replication group master or archival backup after application or system failure.

    When in-memory logs are configured and no more log buffer space is available, Berkeley DB methods may return an additional error value, DB_LOG_BUFFER_FULL. When choosing log buffer and file sizes for in-memory logs, applications should ensure the in-memory log buffer size is large enough that no transaction will ever span the entire buffer, and avoid a state where the in-memory buffer is full and no space can be freed because a transaction that started in the first log "file" is still active.

    Calling DbEnv::set_flags with the DB_LOG_INMEMORY flag affects the database environment, including all threads of control accessing the database environment.

    The DB_LOG_INMEMORY flag may be used to configure Berkeley DB only before the DbEnv::open method is called.

  DB_NOLOCKING
    If set, Berkeley DB will grant all requested mutual exclusion mutexes and database locks without regard for their actual availability. This functionality should never be used for purposes other than debugging.

    Calling DbEnv::set_flags with the DB_NOLOCKING flag only affects the specified DbEnv handle (and any other Berkeley DB handles opened within the scope of that handle).

    The DB_NOLOCKING flag may be used to configure Berkeley DB at any time during the life of the application.

  DB_MULTIVERSION
    If set, all databases in the environment will be opened as if DB_MULTIVERSION is passed to Db::open. This flag will be ignored for queue databases for which DB_MULTIVERSION is not supported.

    Calling DbEnv::set_flags with the DB_MULTIVERSION flag only affects the specified DbEnv handle (and any other Berkeley DB handles opened within the scope of that handle). For consistent behavior across the environment, all DbEnv handles opened in the environment must either set the DB_MULTIVERSION flag or the flag should be specified in the DB_CONFIG configuration file.

    The DB_MULTIVERSION flag may be used to configure Berkeley DB at any time during the life of the application.

  DB_NOMMAP
    If set, Berkeley DB will copy read-only database files into the local cache instead of potentially mapping them into process memory (see the description of the DbEnv::set_mp_mmapsize method for further information).

    Calling DbEnv::set_flags with the DB_NOMMAP flag only affects the specified DbEnv handle (and any other Berkeley DB handles opened within the scope of that handle). For consistent behavior across the environment, all DbEnv handles opened in the environment must either set the DB_NOMMAP flag or the flag should be specified in the DB_CONFIG configuration file.

    The DB_NOMMAP flag may be used to configure Berkeley DB at any time during the life of the application.

  DB_NOPANIC
    If set, Berkeley DB will ignore any panic state in the database environment. (Database environments in a panic state normally refuse all attempts to call Berkeley DB functions, returning DB_RUNRECOVERY.) This functionality should never be used for purposes other than debugging.

    Calling DbEnv::set_flags with the DB_NOPANIC flag only affects the specified DbEnv handle (and any other Berkeley DB handles opened within the scope of that handle).

    The DB_NOPANIC flag may be used to configure Berkeley DB at any time during the life of the application.

  DB_OVERWRITE
    Overwrite files stored in encrypted formats before deleting them. Berkeley DB overwrites files using alternating 0xff, 0x00 and 0xff byte patterns. For file overwriting to be effective, the underlying file must be stored on a fixed-block filesystem. Systems with journaling or logging filesystems will require operating system support and probably modification of the Berkeley DB sources.

    Calling DbEnv::set_flags with the DB_OVERWRITE flag only affects the specified DbEnv handle (and any other Berkeley DB handles opened within the scope of that handle).

    The DB_OVERWRITE flag may be used to configure Berkeley DB at any time during the life of the application.

  DB_PANIC_ENVIRONMENT
    If set, Berkeley DB will set the panic state for the database environment. (Database environments in a panic state normally refuse all attempts to call Berkeley DB functions, returning DB_RUNRECOVERY.) This flag may not be specified using the environment's DB_CONFIG file. This flag may be used to configure Berkeley DB only after the DbEnv::open method is called.

    Calling DbEnv::set_flags with the DB_PANIC_ENVIRONMENT flag affects the database environment, including all threads of control accessing the database environment.

    The DB_PANIC_ENVIRONMENT flag may be used to configure Berkeley DB at any time during the life of the application.

  DB_REGION_INIT
    In some applications, the expense of page-faulting the underlying shared memory regions can affect performance. (For example, if the page-fault occurs while holding a lock, other lock requests can convoy, and overall throughput may decrease.) If set, Berkeley DB will page-fault shared regions into memory when initially creating or joining a Berkeley DB environment. In addition, Berkeley DB will write the shared regions when creating an environment, forcing the underlying virtual memory and filesystems to instantiate both the necessary memory and the necessary disk space. This can also avoid out-of-disk space failures later on.

    Calling DbEnv::set_flags with the DB_REGION_INIT flag only affects the specified DbEnv handle (and any other Berkeley DB handles opened within the scope of that handle). For consistent behavior across the environment, all DbEnv handles opened in the environment must either set the DB_REGION_INIT flag or the flag should be specified in the DB_CONFIG configuration file.

    The DB_REGION_INIT flag may be used to configure Berkeley DB at any time during the life of the application.

  DB_TIME_NOTGRANTED
    If set, database calls timing out based on lock or transaction timeout values will throw a DbLockNotGrantedException exception instead of DbDeadlockException. This allows applications to distinguish between operations which have deadlocked and operations which have exceeded their time limits.

    Calling DbEnv::set_flags with the DB_TIME_NOTGRANTED flag only affects the specified DbEnv handle (and any other Berkeley DB handles opened within the scope of that handle). For consistent behavior across the environment, all DbEnv handles opened in the environment must either set the DB_TIME_NOTGRANTED flag or the flag should be specified in the DB_CONFIG configuration file.

    The DB_TIME_NOTGRANTED flag may be used to configure Berkeley DB at any time during the life of the application.

  DB_TXN_NOSYNC
    If set, Berkeley DB will not write or synchronously flush the log on transaction commit. This means that transactions exhibit the ACI (atomicity, consistency, and isolation) properties, but not D (durability); that is, database integrity will be maintained, but if the application or system fails, it is possible some number of the most recently committed transactions may be undone during recovery. The number of transactions at risk is governed by how many log updates can fit into the log buffer, how often the operating system flushes dirty buffers to disk, and how often the log is checkpointed.

    Calling DbEnv::set_flags with the DB_TXN_NOSYNC flag only affects the specified DbEnv handle (and any other Berkeley DB handles opened within the scope of that handle). For consistent behavior across the environment, all DbEnv handles opened in the environment must either set the DB_TXN_NOSYNC flag or the flag should be specified in the DB_CONFIG configuration file.

    The DB_TXN_NOSYNC flag may be used to configure Berkeley DB at any time during the life of the application.

  DB_TXN_SNAPSHOT
    If set, all transactions in the environment will be started as if DB_TXN_SNAPSHOT were passed to DbEnv::txn_begin, and all non-transactional cursors will be opened as if DB_TXN_SNAPSHOT were passed to Db::cursor.

    Calling DbEnv::set_flags with the DB_TXN_SNAPSHOT flag only affects the specified DbEnv handle (and any other Berkeley DB handles opened within the scope of that handle). For consistent behavior across the environment, all DbEnv handles opened in the environment must either set the DB_TXN_SNAPSHOT flag or the flag should be specified in the DB_CONFIG configuration file.

    The DB_TXN_SNAPSHOT flag may be used to configure Berkeley DB at any time during the life of the application.

  DB_TXN_WRITE_NOSYNC
    If set, Berkeley DB will write, but will not synchronously flush, the log on transaction commit. This means that transactions exhibit the ACI (atomicity, consistency, and isolation) properties, but not D (durability); that is, database integrity will be maintained, but if the system fails, it is possible some number of the most recently committed transactions may be undone during recovery. The number of transactions at risk is governed by how often the system flushes dirty buffers to disk and how often the log is checkpointed.

    Calling DbEnv::set_flags with the DB_TXN_WRITE_NOSYNC flag only affects the specified DbEnv handle (and any other Berkeley DB handles opened within the scope of that handle). For consistent behavior across the environment, all DbEnv handles opened in the environment must either set the DB_TXN_WRITE_NOSYNC flag or the flag should be specified in the DB_CONFIG configuration file.

    The DB_TXN_WRITE_NOSYNC flag may be used to configure Berkeley DB at any time during the life of the application.

  DB_YIELDCPU
    If set, Berkeley DB will yield the processor immediately after each page or mutex acquisition. This functionality should never be used for purposes other than stress testing.

    Calling DbEnv::set_flags with the DB_YIELDCPU flag only affects the specified DbEnv handle (and any other Berkeley DB handles opened within the scope of that handle). For consistent behavior across the environment, all DbEnv handles opened in the environment must either set the DB_YIELDCPU flag or the flag should be specified in the DB_CONFIG configuration file.

    The DB_YIELDCPU flag may be used to configure Berkeley DB at any time during the life of the application.

onoff
  If the onoff parameter is zero, the specified flags are cleared; otherwise they are set.

### Errors

The DbEnv::set_flags method may fail and throw DbException, encapsulating one of the following non-zero errors, or return one of the following non-zero errors:

EINVAL
  An invalid flag value or parameter was specified.

### Description: DbEnv::get_flags

The DbEnv::get_flags method returns the configuration flags.

The DbEnv::get_flags method may be called at any time during the life of the application.

The DbEnv::get_flags method either returns a non-zero error value or throws an exception that encapsulates a non-zero error value on failure, and returns 0 on success.

### Parameters

flagsp
  The DbEnv::get_flags method returns the configuration flags in flagsp.

### Class

DbEnv

### See Also

Database Environments and Related Methods`

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