public void key_range(DbTxn txnid Dbt key, DbKeyRange key_range, int flags) throws DbException;
The Db.key_range method returns an estimate of the proportion of keys that are less than, equal to, and greater than the specified key. The underlying database must be of type Btree.
The information is returned in the key_range argument, which contains three elements of type double: less, equal, and greater. Values are in the range of 0 to 1; for example, if the field less is 0.05, 5% of the keys in the database are less than the key argument. The value for equal will be zero if there is no matching key, and will be non-zero otherwise.
If the operation is to be transaction-protected, the txnid parameter is a transaction handle returned from DbEnv.txn_begin; otherwise, null. The Db.key_range method does not retain the locks it acquires for the life of the transaction, so estimates may not be repeatable.
The flags parameter is currently unused, and must be set to 0.
The Db.key_range method throws an exception that encapsulates a non-zero error value on failure.
The Db.key_range method may fail and throw an exception encapsulating a non-zero error for the following conditions:
The underlying database was not of type Btree.
If the operation was selected to resolve a deadlock, the Db.key_range method will fail and throw a DbDeadlockException exception.
The Db.key_range method may fail and throw an exception for errors specified for other Berkeley DB and C library or system methods. If a catastrophic error has occurred, the Db.key_range method may fail and throw a DbRunRecoveryException, in which case all subsequent Berkeley DB calls will fail in the same way.
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