DbEnv::mutex_set_max()
Prev | Chapter 10. Mutex Methods | Next

## DbEnv::mutex_set_max()

    #include <db_cxx.h>

    int
    DbEnv::mutex_set_max(u_int32_t max);

Configure the total number of mutexes to allocate.

Berkeley DB allocates a default number of mutexes based on the initial configuration of the database environment. That default calculation may be too small if the application has an unusual need for mutexes (for example, if the application opens an unexpectedly large number of databases) or too large (if the application is trying to minimize its memory footprint). The `DbEnv::mutex_set_max()` method is used to specify an absolute number of mutexes to allocate.

Calling the `DbEnv::mutex_set_max()` method discards any value previously set using the `DbEnv::mutex_set_increment()` method.

The database environment's total number of mutexes 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 "mutex_set_max", one or more whitespace characters, and the total number of mutexes. Because the DB_CONFIG file is read when the database environment is opened, it will silently overrule configuration done before that time.

The `DbEnv::mutex_set_max()` method configures a database environment, not only operations performed using the specified DbEnv handle.

The `DbEnv::mutex_set_max()` 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::mutex_set_max()` will be ignored.

The `DbEnv::mutex_set_max()` 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

#### max

The max parameter is the absolute number of mutexes to allocate.

### Errors

The `DbEnv::mutex_set_max()` 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:

#### EINVAL

An invalid flag value or parameter was specified.

### Class

DbEnv

### See Also

Mutex Methods

Prev | Up | Next
DbEnv::mutex_set_increment() | Home | DbEnv::mutex_set_tas_spins()