DB->key_range()

#include <db.h>

int
DB->key_range(DB *db, DB_TXN *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 returns a non-zero error value on failure and 0 on success.

Parameters

txnid

If the operation is part of an application-specified transaction, the txnid parameter is a transaction handle returned from DB_ENV->txn_begin(); if the operation is part of a Berkeley DB Concurrent Data Store group, the txnid parameter is a handle returned from DB_ENV->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.

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.

flags

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

Errors

The DB->key_range() method may fail and return one of the following non-zero errors:

DB_LOCK_DEADLOCK

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

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.

You attempted to open a database handle that is configured for no waiting exclusive locking, but the exclusive lock could not be immediately obtained. See DB->set_lk_exclusive() for more information.

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 return DB_REP_HANDLE_DEAD. The application will need to discard the handle and open a new one in order to continue processing.

DB_REP_LOCKOUT

The operation was blocked by client/master synchronization.

EINVAL

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