<!--$Id: db_key_range.so,v 10.24 2007/10/24 16:06:06 bostic Exp $--> <!--Copyright (c) 1997,2008 Oracle. All rights reserved.--> <!--See the file LICENSE for redistribution information.--> <html> <head> <title>Berkeley DB: Db::key_range</title> <meta name="description" content="Berkeley DB: An embedded database programmatic toolkit."> <meta name="keywords" content="embedded,database,programmatic,toolkit,btree,hash,hashing,transaction,transactions,locking,logging,access method,access methods,Java,C,C++"> </head> <body bgcolor=white> <table width="100%"><tr valign=top> <td> <b>Db::key_range</b> </td> <td align=right> <a href="../api_cxx/api_core.html"><img src="../images/api.gif" alt="API"></a> <a href="../ref/toc.html"><img src="../images/ref.gif" alt="Ref"></a></td> </tr></table> <hr size=1 noshade> <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> <hr size=1 noshade> <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="../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="../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="../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="../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="../ref/program/errorret.html#DB_LOCK_DEADLOCK">DB_LOCK_DEADLOCK</a> or throw a <a href="../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="../ref/program/errorret.html#DB_LOCK_NOTGRANTED">DB_LOCK_NOTGRANTED</a> or throw a <a href="../api_cxx/lockng_class.html">DbLockNotGrantedException</a> exception.</p> <hr size=1 noshade> <br><b>Class</b> <a href="../api_cxx/db_class.html">Db</a> <br><b>See Also</b> <a href="../api_cxx/db_list.html">Databases and Related Methods</a> </tt> <table width="100%"><tr><td><br></td><td align=right> <a href="../api_cxx/api_core.html"><img src="../images/api.gif" alt="API"></a><a href="../ref/toc.html"><img src="../images/ref.gif" alt="Ref"></a> </td></tr></table> <p><font size=1>Copyright (c) 1996,2008 Oracle. 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