#include <db_cxx.h> int DbEnv::log_set_config(u_int32_t flags, int onoff);
The DbEnv::log_set_config() method configures the Berkeley DB
logging subsystem.
The DbEnv::log_set_config() method configures a database
environment, not only operations performed using the specified
DbEnv handle.
The DbEnv::log_set_config() method may be called at any time during
the life of the application.
The DbEnv::log_set_config()
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 flags parameter must be set by bitwise inclusively OR'ing together one or more of the following values:
Turn off system buffering of Berkeley DB log files to avoid double caching.
Calling DbEnv::log_set_config() with the DB_LOG_DIRECT 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_LOG_DIRECT flag or the flag should
be specified in the DB_CONFIG configuration file.
The DB_LOG_DIRECT flag may be used to configure Berkeley DB at any
time during the life of the application.
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::log_set_config() with the DB_LOG_DSYNC 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_LOG_DSYNC flag or the flag should
be specified in the DB_CONFIG configuration file.
The DB_LOG_DSYNC flag may be used to configure Berkeley DB at any time
during the life of the application.
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.
Replication Manager applications operate in a group-aware manner for log file removal, and automatic log file removal simplifies the application.
Replication Base API applications will rarely want to configure automatic log file removal as it increases the likelihood a master will be unable to satisfy a client's request for a recent log record.
Calling DbEnv::log_set_config() with the
DB_LOG_AUTO_REMOVE flag
affects the database environment, including all threads of control
accessing the database environment.
The DB_LOG_AUTO_REMOVE flag may be used to configure Berkeley DB at
any time during the life of the application.
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::log_set_config() with the
DB_LOG_IN_MEMORY flag
affects the database environment, including all threads of control
accessing the database environment.
The DB_LOG_IN_MEMORY flag may be used to configure Berkeley DB only
before the DbEnv::open()
method is called.
DB_LOG_ZERO
If set, zero all pages of a log file when that log file is created. This has shown to provide greater transaction throughput in some environments. The log file will be zeroed by the thread which needs to re-create the new log file. Other threads may not write to the log file while this is happening.
Calling DbEnv::log_set_config() with the
DB_LOG_ZERO flag affects only the current environment handle.
The DB_LOG_ZERO flag may be used to configure Berkeley DB at any time.
The DbEnv::log_set_config()
method may fail and throw a DbException
exception, encapsulating one of the following non-zero errors, or return one
of the following non-zero errors: