DbEnv::set_lk_detect()
Prev | Chapter 7. The DbLock Handle | Next

## DbEnv::set_lk_detect()

    #include <db_cxx.h>

    int
    DbEnv::set_lk_detect(u_int32_t detect);

Set if the deadlock detector is to be run whenever a lock conflict occurs, and specify what lock request(s) should be rejected. As transactions acquire locks on behalf of a single locker ID, rejecting a lock request associated with a transaction normally requires the transaction be aborted.

The database environment's deadlock detector configuration 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_lk_detect", one or more whitespace characters, and the method detect parameter as a string; for example, "set_lk_detect DB_LOCK_OLDEST". 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_lk_detect()` method configures a database environment, not only operations performed using the specified DbEnv handle.

The `DbEnv::set_lk_detect()` method may be called at any time during the life of the application.

The `DbEnv::set_lk_detect()` 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

#### detect

The detect parameter configures the deadlock detector. The specified value must be one of the following list:

- `DB_LOCK_DEFAULT`

  Use whatever lock policy was specified when the database environment was created. If no lock policy has yet been specified, set the lock policy to DB_LOCK_RANDOM.

- `DB_LOCK_EXPIRE`

  Reject lock requests which have timed out. No other deadlock detection is performed.

- `DB_LOCK_MAXLOCKS`

  Reject the lock request for the locker ID with the most locks.

- `DB_LOCK_MAXWRITE`

  Reject the lock request for the locker ID with the most write locks.

- `DB_LOCK_MINLOCKS`

  Reject the lock request for the locker ID with the fewest locks.

- `DB_LOCK_MINWRITE`

  Reject the lock request for the locker ID with the fewest write locks.

- `DB_LOCK_OLDEST`

  Reject the lock request for the locker ID with the oldest lock.

- `DB_LOCK_RANDOM`

  Reject the lock request for a random locker ID.

- `DB_LOCK_YOUNGEST`

  Reject the lock request for the locker ID with the youngest lock.

### Errors

The `DbEnv::set_lk_detect()` 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, DbLock

### See Also

Locking Subsystem and Related Methods

Prev | Up | Next
DbEnv::set_lk_conflicts() | Home | DbEnv::set_lk_max_lockers()