Berkeley DB: DbEnv::set_lk_detect
Description: Berkeley DB: An embedded database programmatic toolkit.
Keywords: embedded,database,programmatic,toolkit,b+tree,btree,hash,hashing,transaction,transactions,locking,logging,access method,access methods,Java,C,C++

### DbEnv::set_lk_detect |

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###

    #include <db_cxx.h>

    int
    DbEnv::set_lk_detect(u_int32_t detect);

    int
    DbEnv::get_lk_detect(u_int32_t *lk_detectp);

### Description: DbEnv::set_lk_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 set 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 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_lk_detect must be consistent with the existing environment or an error will be returned.

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 greatest number of locks.
  DB_LOCK_MINLOCKS
    Reject the lock request for the locker ID with the fewest number of locks.
  DB_LOCK_MINWRITE
    Reject the lock request for the locker ID with the fewest number of write locks.
  DB_LOCK_OLDEST
    Reject the lock request for the oldest locker ID.
  DB_LOCK_RANDOM
    Reject the lock request for a random locker ID.
  DB_LOCK_YOUNGEST
    Reject the lock request for the youngest locker ID.

### Errors

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

EINVAL
  If the method was called after DbEnv::open was called; or if an invalid flag value or parameter was specified.

### Description: DbEnv::get_lk_detect

The DbEnv::get_lk_detect method returns the deadlock detector configuration.

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

The DbEnv::get_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

lk_detectp
  The DbEnv::get_lk_detect method returns the deadlock detector configuration in lk_detectp.

### Class

DbEnv, DbLock

### See Also

Locking Subsystem and Related Methods`

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