1<!--$Id: db_key_range.so,v 10.24 2007/10/24 16:06:06 bostic Exp $--> 2<!--Copyright (c) 1997,2008 Oracle. All rights reserved.--> 3<!--See the file LICENSE for redistribution information.--> 4<html> 5<head> 6<title>Berkeley DB: Db::key_range</title> 7<meta name="description" content="Berkeley DB: An embedded database programmatic toolkit."> 8<meta name="keywords" content="embedded,database,programmatic,toolkit,btree,hash,hashing,transaction,transactions,locking,logging,access method,access methods,Java,C,C++"> 9</head> 10<body bgcolor=white> 11<table width="100%"><tr valign=top> 12<td> 13<b>Db::key_range</b> 14</td> 15<td align=right> 16<a href="/api_cxx/api_core.html"><img src="/images/api.gif" alt="API"></a> 17<a href="/ref/toc.html"><img src="/images/ref.gif" alt="Ref"></a></td> 18</tr></table> 19<hr size=1 noshade> 20<tt> 21<b><pre> 22#include <db_cxx.h> 23<p> 24int 25Db::key_range(DbTxn *txnid 26 Dbt *key, DB_KEY_RANGE *key_range, u_int32_t flags); 27</pre></b> 28<hr size=1 noshade> 29<b>Description: Db::key_range</b> 30<p>The Db::key_range method returns an estimate of the proportion of keys 31that are less than, equal to, and greater than the specified key. The 32underlying database must be of type Btree.</p> 33<p>The Db::key_range method fills in a structure of type DB_KEY_RANGE. The 34following data fields are available from the DB_KEY_RANGE structure:</p> 35<br> 36<b>double less;</b><ul compact><li>A value between 0 and 1, the proportion of keys less than the specified 37key.</ul> 38<b>double equal;</b><ul compact><li>A value between 0 and 1, the proportion of keys equal to the specified 39key.</ul> 40<b>double greater;</b><ul compact><li>A value between 0 and 1, the proportion of keys greater than the 41specified key.</ul> 42<br> 43<p>Values are in the range of 0 to 1; for example, if the field 44<b>less</b> is 0.05, 5% of the keys in the database are less than the 45<b>key</b> parameter. The value for <b>equal</b> will be zero if 46there is no matching key, and will be non-zero otherwise.</p> 47<p>The Db::key_range method 48either returns a non-zero error value 49or throws an exception that encapsulates a non-zero error value on 50failure, and returns 0 on success. 51</p> 52<b>Parameters</b> <br> 53 <b>key</b><ul compact><li>The key <a href="/api_cxx/dbt_class.html">Dbt</a> operated on.</ul> 54 <b>key_range</b><ul compact><li>The estimates are returned in the <b>key_range</b> parameter, which 55contains three elements of type double: <b>less</b>, <b>equal</b>, and 56<b>greater</b>. Values are in the range of 0 to 1; for example, if the 57field <b>less</b> is 0.05, 5% of the keys in the database are less than 58the <b>key</b> parameter. The value for <b>equal</b> will be zero if 59there is no matching key, and will be non-zero otherwise.</ul> 60 <b>txnid</b><ul compact><li>If the operation is part of an application-specified transaction, the 61<b>txnid</b> parameter is a transaction handle returned from 62<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 63<b>txnid</b> parameter is a handle returned from 64<a href="/api_cxx/env_cdsgroup_begin.html">DbEnv::cdsgroup_begin</a>; otherwise NULL. 65If no transaction handle is 66specified, but the 67operation occurs in a transactional 68database, 69the operation will be implicitly transaction protected. 70The Db::key_range method does not retain the locks it acquires for the 71life of the transaction, so estimates may not be repeatable.</ul> 72 <b>flags</b><ul compact><li>The <b>flags</b> parameter is currently unused, and must be set to 0.</ul> 73<br> 74<br><b>Errors</b> 75<p>The Db::key_range method 76may fail and throw 77<a href="/api_cxx/except_class.html">DbException</a>, 78encapsulating one of the following non-zero errors, or return one of 79the following non-zero errors:</p> 80<br> 81<b>DB_REP_HANDLE_DEAD</b><ul compact><li>The database handle has been invalidated because a replication election 82unrolled a committed transaction.</ul> 83<br> 84<br> 85<b>DB_REP_LOCKOUT</b><ul compact><li>The operation was blocked by client/master synchronization.</ul> 86<br> 87<br> 88<b>EINVAL</b><ul compact><li>If the underlying database was not of type Btree; or if an 89invalid flag value or parameter was specified.</ul> 90<br> 91<p>If a transactional database environment operation was selected to 92resolve a deadlock, the Db::key_range method will fail and 93either return <a href="/ref/program/errorret.html#DB_LOCK_DEADLOCK">DB_LOCK_DEADLOCK</a> or 94throw a <a href="/api_cxx/deadlock_class.html">DbDeadlockException</a> exception.</p> 95<p>If a Berkeley DB Concurrent Data Store database environment configured for lock timeouts was unable 96to grant a lock in the allowed time, the Db::key_range method will fail and 97either return <a href="/ref/program/errorret.html#DB_LOCK_NOTGRANTED">DB_LOCK_NOTGRANTED</a> or 98throw a <a href="/api_cxx/lockng_class.html">DbLockNotGrantedException</a> exception.</p> 99<hr size=1 noshade> 100<br><b>Class</b> 101<a href="/api_cxx/db_class.html">Db</a> 102<br><b>See Also</b> 103<a href="/api_cxx/db_list.html">Databases and Related Methods</a> 104</tt> 105<table width="100%"><tr><td><br></td><td align=right> 106<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> 107</td></tr></table> 108<p><font size=1>Copyright (c) 1996,2008 Oracle. All rights reserved.</font> 109</body> 110</html> 111
