Library Version 12.1.6.0

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 either before or after environment open, but once it is set it may not be changed again during the environment's lifetime.

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 deadlock detector will reject the lock request with the lowest priority. If multiple lock requests have the lowest priority, then the detect parameter is used to select which of those lock requests to reject. 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()