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<b>Db::key_range</b>
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<tt>
<b><pre>
#include <db_cxx.h>
<p>
int
Db::key_range(DbTxn *txnid
Dbt *key, DB_KEY_RANGE *key_range, u_int32_t flags);
</pre></b>
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<b>Description: Db::key_range</b>
<p>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.</p>
<p>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:</p>
<br>
<b>double less;</b><ul compact><li>A value between 0 and 1, the proportion of keys less than the specified
key.</ul>
<b>double equal;</b><ul compact><li>A value between 0 and 1, the proportion of keys equal to the specified
key.</ul>
<b>double greater;</b><ul compact><li>A value between 0 and 1, the proportion of keys greater than the
specified key.</ul>
<br>
<p>Values are in the range of 0 to 1; for example, if the field
<b>less</b> is 0.05, 5% of the keys in the database are less than the
<b>key</b> parameter. The value for <b>equal</b> will be zero if
there is no matching key, and will be non-zero otherwise.</p>
<p>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.
</p>
<b>Parameters</b> <br>
<b>key</b><ul compact><li>The key <a href="../../db4-devel-4.7.25/api_cxx/dbt_class.html">Dbt</a> operated on.</ul>
<b>key_range</b><ul compact><li>The estimates are returned in the <b>key_range</b> parameter, which
contains three elements of type double: <b>less</b>, <b>equal</b>, and
<b>greater</b>. Values are in the range of 0 to 1; for example, if the
field <b>less</b> is 0.05, 5% of the keys in the database are less than
the <b>key</b> parameter. The value for <b>equal</b> will be zero if
there is no matching key, and will be non-zero otherwise.</ul>
<b>txnid</b><ul compact><li>If the operation is part of an application-specified transaction, the
<b>txnid</b> 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
<b>txnid</b> 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>
<b>flags</b><ul compact><li>The <b>flags</b> parameter is currently unused, and must be set to 0.</ul>
<br>
<br><b>Errors</b>
<p>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:</p>
<br>
<b>DB_REP_HANDLE_DEAD</b><ul compact><li>The database handle has been invalidated because a replication election
unrolled a committed transaction.</ul>
<br>
<br>
<b>DB_REP_LOCKOUT</b><ul compact><li>The operation was blocked by client/master synchronization.</ul>
<br>
<br>
<b>EINVAL</b><ul compact><li>If the underlying database was not of type Btree; or if an
invalid flag value or parameter was specified.</ul>
<br>
<p>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.</p>
<p>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.</p>
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<br><b>Class</b>
<a href="../../db4-devel-4.7.25/api_cxx/db_class.html">Db</a>
<br><b>See Also</b>
<a href="../../db4-devel-4.7.25/api_cxx/db_list.html">Databases and Related Methods</a>
</tt>
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