Db::key_range()
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## Db::key_range()

    #include <db_cxx.h>

    int
    Db::key_range(DbTxn *txnid
        Dbt *key, DB_KEY_RANGE *key_range, u_int32_t flags);

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 `Db::key_range()` method fills in a structure of type DB_KEY_RANGE. The following data fields are available from the DB_KEY_RANGE structure:

- double less;

  A value between 0 and 1, the proportion of keys less than the specified key.

- double equal;

  A value between 0 and 1, the proportion of keys equal to the specified key.

- double greater;

  A value between 0 and 1, the proportion of keys greater than the specified key.

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 parameter. The value for equal will be zero if there is no matching key, and will be non-zero otherwise.

The `Db::key_range()` 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

#### key

The key Dbt operated on.

#### key_range

The estimates are returned in the key_range parameter, 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 parameter. The value for equal will be zero if there is no matching key, and will be non-zero otherwise.

#### txnid

If the operation is part of an application-specified transaction, the txnid parameter is a transaction handle returned from DbEnv::txn_begin(); if the operation is part of a Berkeley DB Concurrent Data Store group, the txnid parameter is a handle returned from DbEnv::cdsgroup_begin(); otherwise NULL. If no transaction handle is specified, but the operation occurs in a transactional database, the operation will be implicitly transaction protected. The `Db::key_range()` method does not retain the locks it acquires for the life of the transaction, so estimates may not be repeatable.

#### flags

The flags parameter is currently unused, and must be set to 0.

### Errors

The `Db::key_range()` 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:

#### DbDeadlockException or DB_LOCK_DEADLOCK

A transactional database environment operation was selected to resolve a deadlock.

DbDeadlockException is thrown if your Berkeley DB API is configured to throw exceptions. Otherwise, `DB_LOCK_DEADLOCK` is returned.

#### DbLockNotGrantedException or DB_LOCK_NOTGRANTED

A Berkeley DB Concurrent Data Store database environment configured for lock timeouts was unable to grant a lock in the allowed time.

DbLockNotGrantedException is thrown if your Berkeley DB API is configured to throw exceptions. Otherwise, `DB_LOCK_NOTGRANTED` is returned.

#### DbRepHandleDeadException or DB_REP_HANDLE_DEAD

When a client synchronizes with the master, it is possible for committed transactions to be rolled back. This invalidates all the database and cursor handles opened in the replication environment. Once this occurs, an attempt to use such a handle will throw a DbRepHandleDeadException (if your application is configured to throw exceptions), or return `DB_REP_HANDLE_DEAD`. The application will need to discard the handle and open a new one in order to continue processing.

#### DbDeadlockException or DB_REP_LOCKOUT

The operation was blocked by client/master synchronization.

DbDeadlockException is thrown if your Berkeley DB API is configured to throw exceptions. Otherwise, `DB_REP_LOCKOUT` is returned.

#### EINVAL

If the underlying database was not of type Btree; or if an invalid flag value or parameter was specified.

### Class

Db

### See Also

Database and Related Methods

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