Berkeley DB: DbEnv::set_flags
Description: Berkeley DB: An embedded database programmatic toolkit.
Keywords: embedded,database,programmatic,toolkit,b+tree,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);

# Description

The flags value must be set to 0 or by bitwise inclusively OR'ing together one or more of the following values: If onoff is zero, the specified flags are cleared; otherwise they are set.

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

  This call affects only the specified DbEnv handle (and any handles opened within the scope of that handle). For consistent behavior across the environment, all DbEnv handles opened in the environment must either make this same call or the DB_CDB_ALLDB flag should be specified in the DB_CONFIG configuration file.

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.

  This call affects only the specified DbEnv handle (and any handles opened within the scope of that handle).

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).

  This call affects only the specified DbEnv handle (and any handles opened within the scope of that handle). For consistent behavior across the environment, all DbEnv handles opened in the environment must either make this same call or the DB_NOMMAP flag should be specified in the DB_CONFIG configuration file.

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.

  This call affects only the specified DbEnv handle (and any handles opened within the scope of that handle).

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 interface is called.

  This call affects all threads of control using the database environment.

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.

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

  This call affects only the specified DbEnv handle (and any handles opened within the scope of that handle). For consistent behavior across the environment, all DbEnv handles opened in the environment must either make this same call or the DB_REGION_INIT flag should be specified in the DB_CONFIG configuration file.

DB_TXN_NOSYNC
  If set, Berkeley DB will not synchronously flush the log on transaction commit or prepare. This means that transactions exhibit the ACI (atomicity, consistency, and isolation) properties, but not D (durability); that is, database integrity will be maintained, but it is possible that some number of the most recently committed transactions may be undone during recovery. The number of transactions potentially at risk is governed by how often the log is checkpointed (see db_checkpoint for more information) and how many log updates can fit into the log buffer.

  This call affects only the specified DbEnv handle (and any handles opened within the scope of that handle). For consistent behavior across the environment, all DbEnv handles opened in the environment must either make this same call or the DB_TXN_NOSYNC flag should be specified in the DB_CONFIG configuration file.

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.

  This call affects only the specified DbEnv handle (and any handles opened within the scope of that handle). For consistent behavior across the environment, all DbEnv handles opened in the environment must either make this same call or the DB_YIELDCPU flag should be specified in the DB_CONFIG configuration file.

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.

The database environment's flag values may also be set 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 interface flag argument 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.

# Errors

The DbEnv::set_flags method may fail and throw an exception or return a non-zero error for the following conditions:

EINVAL
  An invalid flag value or parameter was specified.

The DbEnv::set_flags method may fail and throw an exception or return a non-zero error for errors specified for other Berkeley DB and C library or system methods. If a catastrophic error has occurred, the DbEnv::set_flags method may fail and either return DB_RUNRECOVERY or throw an exception encapsulating DB_RUNRECOVERY, in which case all subsequent Berkeley DB calls will fail in the same way.

# Class

DbEnv

# See Also

DbEnv::close, DbEnv::err, DbEnv::errx DbEnv::open, DbEnv::remove, DbEnv::set_alloc, DbEnv::set_cachesize, DbEnv::set_data_dir, DbEnv::set_errcall, DbEnv::set_errfile, DbEnv::set_error_stream, DbEnv::set_errpfx, DbEnv::set_feedback, DbEnv::set_flags, DbEnv::set_paniccall, DbEnv::set_recovery_init, DbEnv::set_rpc_server, DbEnv::set_shm_key, DbEnv::set_tas_spins, DbEnv::set_tmp_dir, DbEnv::set_timeout, DbEnv::set_verbose, DbEnv::strerror and DbEnv::version.`

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