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Db::key_range
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#include &lt;db_cxx.h&gt;

int
Db::key_range(DbTxn *txnid
 Dbt *key, DB_KEY_RANGE *key_range, u_int32_t flags);
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Description: Db::key_range
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;<ul compact><li>A value between 0 and 1, the proportion of keys less than the specified
key.</ul>
double equal;<ul compact><li>A value between 0 and 1, the proportion of keys equal to the specified
key.</ul>
double greater;<ul compact><li>A value between 0 and 1, the proportion of keys greater than the
specified key.</ul>
 
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<ul compact><li>The key <a href="../../db4-devel-4.7.25/api_cxx/dbt_class.html">Dbt</a> operated on.</ul>
 key_range<ul compact><li>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.</ul>
 txnid<ul compact><li>If the operation is part of an application-specified transaction, the
txnid parameter is a transaction handle returned from
<a href="../../db4-devel-4.7.25/api_cxx/txn_begin.html">DbEnv::txn_begin</a>; if the operation is part of a Berkeley DB Concurrent Data Store group, the
txnid parameter is a handle returned from
<a href="../../db4-devel-4.7.25/api_cxx/env_cdsgroup_begin.html">DbEnv::cdsgroup_begin</a>; 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.</ul>
 flags<ul compact><li>The flags parameter is currently unused, and must be set to 0.</ul>
 
 Errors
The Db::key_range method
may fail and throw
<a href="../../db4-devel-4.7.25/api_cxx/except_class.html">DbException</a>,
encapsulating one of the following non-zero errors, or return one of
the following non-zero errors:
 
DB_REP_HANDLE_DEAD<ul compact><li>The database handle has been invalidated because a replication election
unrolled a committed transaction.</ul>
 
 
DB_REP_LOCKOUT<ul compact><li>The operation was blocked by client/master synchronization.</ul>
 
 
EINVAL<ul compact><li>If the underlying database was not of type Btree; or if an
invalid flag value or parameter was specified.</ul>
 
If a transactional database environment operation was selected to
resolve a deadlock, the Db::key_range method will fail and
either return <a href="../../db4-devel-4.7.25/ref/program/errorret.html#DB_LOCK_DEADLOCK">DB_LOCK_DEADLOCK</a> or
throw a <a href="../../db4-devel-4.7.25/api_cxx/deadlock_class.html">DbDeadlockException</a> exception.
If a Berkeley DB Concurrent Data Store database environment configured for lock timeouts was unable
to grant a lock in the allowed time, the Db::key_range method will fail and
either return <a href="../../db4-devel-4.7.25/ref/program/errorret.html#DB_LOCK_NOTGRANTED">DB_LOCK_NOTGRANTED</a> or
throw a <a href="../../db4-devel-4.7.25/api_cxx/lockng_class.html">DbLockNotGrantedException</a> exception.
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 Class
<a href="../../db4-devel-4.7.25/api_cxx/db_class.html">Db</a>
 See Also
<a href="../../db4-devel-4.7.25/api_cxx/db_list.html">Databases and Related Methods</a>
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