#include <db_cxx.h>

int
DbEnv::set_lg_bsize(u_int32_t lg_bsize);

int
DbEnv::get_lg_bsize(u_int32_t *lg_bsizep);

Set the size of the in-memory log buffer, in bytes.

When the logging subsystem is configured for on-disk logging, the default size of the in-memory log buffer is approximately 32KB. Log information is stored in-memory until the storage space fills up or transaction commit forces the information to be flushed to stable storage. In the presence of long-running transactions or transactions producing large amounts of data, larger buffer sizes can increase throughput.

When the logging subsystem is configured for in-memory logging, the default size of the in-memory log buffer is 1MB. Log information is stored in-memory until the storage space fills up or transaction abort or commit frees up the memory for new transactions. In the presence of long-running transactions or transactions producing large amounts of data, the buffer size must be sufficient to hold all log information that can accumulate during the longest running transaction. 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.

The database environment's log buffer size 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_lg_bsize", one or more whitespace characters, and the size in bytes. 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_lg_bsize method configures a database environment, not only operations performed using the specified DbEnv handle.

The DbEnv::set_lg_bsize method may not be called after the DbEnv::open method is called. If the database environment already exists when DbEnv::open is called, the information specified to DbEnv::set_lg_bsize will be ignored.

The DbEnv::set_lg_bsize 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 lg_bsize parameter is the size of the in-memory log buffer, in bytes.

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

• An invalid flag value or parameter was specified.

The DbEnv::get_lg_bsize method returns the size of the log buffer, in bytes.

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

The DbEnv::get_lg_bsize 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 DbEnv::get_lg_bsize method returns the size of the log buffer, in bytes in lg_bsizep.