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_c/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.h> 23<p> 24int 25DB->key_range(DB *db, DB_TXN *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 48returns a non-zero error value on failure 49and 0 on success. 50</p> 51<b>Parameters</b> <br> 52 <b>key</b><ul compact><li>The key <a href="../api_c/dbt_class.html">DBT</a> operated on.</ul> 53 <b>key_range</b><ul compact><li>The estimates are returned in the <b>key_range</b> parameter, which 54contains three elements of type double: <b>less</b>, <b>equal</b>, and 55<b>greater</b>. Values are in the range of 0 to 1; for example, if the 56field <b>less</b> is 0.05, 5% of the keys in the database are less than 57the <b>key</b> parameter. The value for <b>equal</b> will be zero if 58there is no matching key, and will be non-zero otherwise.</ul> 59 <b>txnid</b><ul compact><li>If the operation is part of an application-specified transaction, the 60<b>txnid</b> parameter is a transaction handle returned from 61<a href="../api_c/txn_begin.html">DB_ENV->txn_begin</a>; if the operation is part of a Berkeley DB Concurrent Data Store group, the 62<b>txnid</b> parameter is a handle returned from 63<a href="../api_c/env_cdsgroup_begin.html">DB_ENV->cdsgroup_begin</a>; otherwise NULL. 64If no transaction handle is 65specified, but the 66operation occurs in a transactional 67database, 68the operation will be implicitly transaction protected. 69The DB->key_range method does not retain the locks it acquires for the 70life of the transaction, so estimates may not be repeatable.</ul> 71 <b>flags</b><ul compact><li>The <b>flags</b> parameter is currently unused, and must be set to 0.</ul> 72<br> 73<br><b>Errors</b> 74<p>The DB->key_range method 75may fail and return one of the following non-zero errors:</p> 76<br> 77<b>DB_LOCK_DEADLOCK</b><ul compact><li>A transactional database environment operation was selected to resolve 78a deadlock.</ul> 79<b>DB_LOCK_NOTGRANTED</b><ul compact><li>A Berkeley DB Concurrent Data Store database environment configured for lock timeouts was unable 80to grant a lock in the allowed time.</ul> 81<br> 82<br> 83<b>DB_REP_HANDLE_DEAD</b><ul compact><li>The database handle has been invalidated because a replication election 84unrolled a committed transaction.</ul> 85<br> 86<br> 87<b>DB_REP_LOCKOUT</b><ul compact><li>The operation was blocked by client/master synchronization.</ul> 88<br> 89<br> 90<b>EINVAL</b><ul compact><li>If the underlying database was not of type Btree; or if an 91invalid flag value or parameter was specified.</ul> 92<br> 93<hr size=1 noshade> 94<br><b>Class</b> 95<a href="../api_c/db_class.html">DB</a> 96<br><b>See Also</b> 97<a href="../api_c/db_list.html">Databases and Related Methods</a> 98</tt> 99<table width="100%"><tr><td><br></td><td align=right> 100<a href="../api_c/api_core.html"><img src="../images/api.gif" alt="API"></a><a href="../ref/toc.html"><img src="../images/ref.gif" alt="Ref"></a> 101</td></tr></table> 102<p><font size=1>Copyright (c) 1996,2008 Oracle. All rights reserved.</font> 103</body> 104</html> 105
