111 lines
5.2 KiB
HTML
111 lines
5.2 KiB
HTML
<!--$Id: db_key_range.html 63573 2008-05-23 21:43:21Z trent.nelson $-->
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<!--Copyright (c) 1997,2008 Oracle. All rights reserved.-->
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<html>
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<head>
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<title>Berkeley DB: Db::key_range</title>
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<meta name="description" content="Berkeley DB: An embedded database programmatic toolkit.">
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<meta name="keywords" content="embedded,database,programmatic,toolkit,btree,hash,hashing,transaction,transactions,locking,logging,access method,access methods,Java,C,C++">
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</head>
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<body bgcolor=white>
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<table width="100%"><tr valign=top>
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<td>
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<b>Db::key_range</b>
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</td>
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<td align=right>
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<a href="../api_cxx/api_core.html"><img src="../images/api.gif" alt="API"></a>
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<a href="../ref/toc.html"><img src="../images/ref.gif" alt="Ref"></a></td>
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</tr></table>
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<hr size=1 noshade>
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<tt>
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<b><pre>
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#include <db_cxx.h>
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<p>
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int
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Db::key_range(DbTxn *txnid
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Dbt *key, DB_KEY_RANGE *key_range, u_int32_t flags);
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</pre></b>
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<hr size=1 noshade>
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<b>Description: Db::key_range</b>
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<p>The Db::key_range method returns an estimate of the proportion of keys
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that are less than, equal to, and greater than the specified key. The
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underlying database must be of type Btree.</p>
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<p>The Db::key_range method fills in a structure of type DB_KEY_RANGE. The
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following data fields are available from the DB_KEY_RANGE structure:</p>
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<br>
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<b>double less;</b><ul compact><li>A value between 0 and 1, the proportion of keys less than the specified
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key.</ul>
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<b>double equal;</b><ul compact><li>A value between 0 and 1, the proportion of keys equal to the specified
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key.</ul>
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<b>double greater;</b><ul compact><li>A value between 0 and 1, the proportion of keys greater than the
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specified key.</ul>
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<br>
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<p>Values are in the range of 0 to 1; for example, if the field
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<b>less</b> is 0.05, 5% of the keys in the database are less than the
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<b>key</b> parameter. The value for <b>equal</b> will be zero if
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there is no matching key, and will be non-zero otherwise.</p>
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<p>The Db::key_range method
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either returns a non-zero error value
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or throws an exception that encapsulates a non-zero error value on
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failure, and returns 0 on success.
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</p>
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<b>Parameters</b> <br>
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<b>key</b><ul compact><li>The key <a href="../api_cxx/dbt_class.html">Dbt</a> operated on.</ul>
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<b>key_range</b><ul compact><li>The estimates are returned in the <b>key_range</b> parameter, which
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contains three elements of type double: <b>less</b>, <b>equal</b>, and
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<b>greater</b>. Values are in the range of 0 to 1; for example, if the
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field <b>less</b> is 0.05, 5% of the keys in the database are less than
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the <b>key</b> parameter. The value for <b>equal</b> will be zero if
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there is no matching key, and will be non-zero otherwise.</ul>
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<b>txnid</b><ul compact><li>If the operation is part of an application-specified transaction, the
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<b>txnid</b> parameter is a transaction handle returned from
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<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
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<b>txnid</b> parameter is a handle returned from
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<a href="../api_cxx/env_cdsgroup_begin.html">DbEnv::cdsgroup_begin</a>; otherwise NULL.
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If no transaction handle is
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specified, but the
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operation occurs in a transactional
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database,
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the operation will be implicitly transaction protected.
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The Db::key_range method does not retain the locks it acquires for the
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life of the transaction, so estimates may not be repeatable.</ul>
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<b>flags</b><ul compact><li>The <b>flags</b> parameter is currently unused, and must be set to 0.</ul>
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<br>
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<br><b>Errors</b>
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<p>The Db::key_range method
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may fail and throw
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<a href="../api_cxx/except_class.html">DbException</a>,
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encapsulating one of the following non-zero errors, or return one of
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the following non-zero errors:</p>
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<br>
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<b>DB_REP_HANDLE_DEAD</b><ul compact><li>The database handle has been invalidated because a replication election
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unrolled a committed transaction.</ul>
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<br>
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<br>
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<b>DB_REP_LOCKOUT</b><ul compact><li>The operation was blocked by client/master synchronization.</ul>
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<br>
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<br>
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<b>EINVAL</b><ul compact><li>If the underlying database was not of type Btree; or if an
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invalid flag value or parameter was specified.</ul>
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<br>
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<p>If a transactional database environment operation was selected to
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resolve a deadlock, the Db::key_range method will fail and
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either return <a href="../ref/program/errorret.html#DB_LOCK_DEADLOCK">DB_LOCK_DEADLOCK</a> or
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throw a <a href="../api_cxx/deadlock_class.html">DbDeadlockException</a> exception.</p>
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<p>If a Berkeley DB Concurrent Data Store database environment configured for lock timeouts was unable
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to grant a lock in the allowed time, the Db::key_range method will fail and
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either return <a href="../ref/program/errorret.html#DB_LOCK_NOTGRANTED">DB_LOCK_NOTGRANTED</a> or
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throw a <a href="../api_cxx/lockng_class.html">DbLockNotGrantedException</a> exception.</p>
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<hr size=1 noshade>
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<br><b>Class</b>
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<a href="../api_cxx/db_class.html">Db</a>
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<br><b>See Also</b>
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<a href="../api_cxx/db_list.html">Databases and Related Methods</a>
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</tt>
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<table width="100%"><tr><td><br></td><td align=right>
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<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>
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</td></tr></table>
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<p><font size=1>Copyright (c) 1996,2008 Oracle. All rights reserved.</font>
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