| Current Path : /usr/share/doc/db4-devel-4.7.25/api_c/ |
| Current File : //usr/share/doc/db4-devel-4.7.25/api_c/db_get.html |
<!--$Id: db_get.so,v 10.95 2007/11/07 16:51:38 bostic Exp $-->
<!--Copyright (c) 1997,2008 Oracle. All rights reserved.-->
<!--See the file LICENSE for redistribution information.-->
<html>
<head>
<title>Berkeley DB: DB->get</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->get</b>
</td>
<td align=right>
<a href="../../db4-devel-4.7.25/api_c/api_core.html"><img src="../../db4-devel-4.7.25/images/api.gif" alt="API"></a>
<a href="../../db4-devel-4.7.25/ref/toc.html"><img src="../../db4-devel-4.7.25/images/ref.gif" alt="Ref"></a></td>
</tr></table>
<hr size=1 noshade>
<tt>
<b><pre>
#include <db.h>
<p>
int
DB->get(DB *db,
DB_TXN *txnid, DBT *key, DBT *data, u_int32_t flags);
<p>
int
DB->pget(DB *db,
DB_TXN *txnid, DBT *key, DBT *pkey, DBT *data, u_int32_t flags);
</pre></b>
<hr size=1 noshade>
<b>Description: DB->get</b>
<p>The DB->get method retrieves key/data pairs from the database. The
address and length of the data associated with the specified <b>key</b>
are returned in the structure to which <b>data</b> refers.</p>
<p>In the presence of duplicate key values, DB->get will return the
first data item for the designated key. Duplicates are sorted by insert
order, except where this order has been overridden by cursor operations.
<b>Retrieval of duplicates requires the use of cursor operations.</b>
See <a href="../../db4-devel-4.7.25/api_c/dbc_get.html">DBcursor->get</a> for details.</p>
<p>When called on a database that has been made into a secondary index
using the <a href="../../db4-devel-4.7.25/api_c/db_associate.html">DB->associate</a> method, the DB->get and
DB->pget methods return the key from the secondary index and the data
item from the primary database. In addition, the DB->pget method
returns the key from the primary database. In databases that are not
secondary indices, the DB->pget method will always fail.</p>
<p>The DB->get method will return <a href="../../db4-devel-4.7.25/ref/program/errorret.html#DB_NOTFOUND">DB_NOTFOUND</a> if the specified key is not in the database.
The DB->get method will return <a href="../../db4-devel-4.7.25/ref/program/errorret.html#DB_KEYEMPTY">DB_KEYEMPTY</a> if the database is a Queue or Recno database and
the specified key exists, but was never explicitly created by the
application or was later deleted.
Unless otherwise specified, the DB->get method
returns a non-zero error value on failure
and 0 on success.
</p>
<b>Parameters</b> <br>
<b>data</b><ul compact><li>The data <a href="../../db4-devel-4.7.25/api_c/dbt_class.html">DBT</a> operated on.</ul>
<b>flags</b><ul compact><li>The <b>flags</b> parameter must be set to 0 or
one of the following values:
<br>
<b><a name="DB_CONSUME">DB_CONSUME</a></b><ul compact><li>Return the record number and data from the available record closest to
the head of the queue, and delete the record. The record number will
be returned in <b>key</b>, as described in <a href="../../db4-devel-4.7.25/api_c/dbt_class.html">DBT</a>. The data will
be returned in the <b>data</b> parameter. A record is available if it
is not deleted and is not currently locked. The underlying database
must be of type Queue for DB_CONSUME to be specified.</ul>
<b><a name="DB_CONSUME_WAIT">DB_CONSUME_WAIT</a></b><ul compact><li>The DB_CONSUME_WAIT flag is the same as the DB_CONSUME
flag, except that if the Queue database is empty, the thread of control
will wait until there is data in the queue before returning. The
underlying database must be of type Queue for DB_CONSUME_WAIT
to be specified.
<p>If lock or transaction timeouts have been specified, the DB->get method
with the DB_CONSUME_WAIT flag
may return <a href="../../db4-devel-4.7.25/ref/program/errorret.html#DB_LOCK_NOTGRANTED">DB_LOCK_NOTGRANTED</a>.
This failure, by itself, does not require the enclosing transaction be
aborted.</p></ul>
<b><a name="DB_GET_BOTH">DB_GET_BOTH</a></b><ul compact><li>Retrieve the key/data pair only if both the key and data match the
arguments.
<p>When used with the DB->pget method version of this method on a
secondary index handle, return the secondary key/primary key/data tuple
only if both the primary and secondary keys match the arguments. It is
an error to use the DB_GET_BOTH flag with the DB->get
version of this method and a secondary index handle.</p></ul>
<b><a name="DB_SET_RECNO">DB_SET_RECNO</a></b><ul compact><li>Retrieve the specified numbered key/data pair from a database. Upon
return, both the <b>key</b> and <b>data</b> items will have been
filled in.
<p>The <b>data</b> field of the specified <b>key</b> must be a pointer
to a logical record number (that is, a <b>db_recno_t</b>). This record
number determines the record to be retrieved.</p>
<p>For DB_SET_RECNO to be specified, the underlying database must be
of type Btree, and it must have been created with the DB_RECNUM flag.</p></ul>
<br>
In addition, the following flags may be set by
bitwise inclusively <b>OR</b>'ing them into the <b>flags</b> parameter:
<br>
<b><a name="DB_IGNORE_LEASE">DB_IGNORE_LEASE</a></b><ul compact><li>Return the data item irrespective of the state of master leases. The
item will be returned under all conditions: if master leases are not
configured, if the request is made to a client, if the request is made
to a master with a valid lease, or if the request is made to a master
without a valid lease.</ul>
<b><a name="DB_MULTIPLE">DB_MULTIPLE</a></b><ul compact><li>Return multiple data items in the buffer to which the <b>data</b>
parameter refers.
<p>In the case of Btree or Hash databases, all of the data items associated
with the specified key are entered into the buffer. In the case of
Queue or Recno databases, all of the data items in the database,
starting at, and subsequent to, the specified key, are entered into the
buffer.</p>
<p>The buffer to which the <b>data</b> parameter refers must be provided
from user memory (see <a href="../../db4-devel-4.7.25/api_c/dbt_class.html#DB_DBT_USERMEM">DB_DBT_USERMEM</a>). The buffer must be at
least as large as the page size of the underlying database, aligned for
unsigned integer access, and be a multiple of 1024 bytes in size. If
the buffer size is insufficient, then upon return from the call the size
field of the <b>data</b> parameter will have been set to an estimated
buffer size, and the error DB_BUFFER_SMALL is returned. (The size is an estimate as the
exact size needed may not be known until all entries are read. It is
best to initially provide a relatively large buffer, but applications
should be prepared to resize the buffer as necessary and repeatedly call
the method.)</p>
<p>The DB_MULTIPLE flag may only be used alone, or with the
DB_GET_BOTH and DB_SET_RECNO options. The
DB_MULTIPLE flag may not be used when accessing databases made
into secondary indices using the <a href="../../db4-devel-4.7.25/api_c/db_associate.html">DB->associate</a> method.</p>
<p>See
<a href="../../db4-devel-4.7.25/api_c/dbt_bulk.html#DB_MULTIPLE_INIT">DB_MULTIPLE_INIT</a>
for more information.</p></ul>
<b><a name="DB_READ_COMMITTED">DB_READ_COMMITTED</a></b><ul compact><li>Configure a transactional get operation to have degree 2 isolation (the
read is not repeatable).</ul>
<b><a name="DB_READ_UNCOMMITTED">DB_READ_UNCOMMITTED</a></b><ul compact><li>Configure a transactional get operation to have degree 1 isolation,
reading modified but not yet committed data. Silently ignored if the
<a href="../../db4-devel-4.7.25/api_c/db_open.html#DB_READ_UNCOMMITTED">DB_READ_UNCOMMITTED</a> flag was not specified when the underlying
database was opened.</ul>
<b><a name="DB_RMW">DB_RMW</a></b><ul compact><li>Acquire write locks instead of read locks when doing the read, if
locking is configured. Setting this flag can eliminate deadlock during
a read-modify-write cycle by acquiring the write lock during the read
part of the cycle so that another thread of control acquiring a read
lock for the same item, in its own read-modify-write cycle, will not
result in deadlock.
<p>Because the DB->get method will not hold locks across
Berkeley DB calls in non-transactional operations, the <a href="../../db4-devel-4.7.25/api_c/dbc_get.html#DB_RMW">DB_RMW</a> flag
to the DB->get call is meaningful only in the presence of
transactions.</p></ul>
<br></ul>
<b>key</b><ul compact><li>The key <a href="../../db4-devel-4.7.25/api_c/dbt_class.html">DBT</a> operated on.</ul>
<b>pkey</b><ul compact><li>The <b>pkey</b> parameter is the return key from the primary database.</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_c/txn_begin.html">DB_ENV->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_c/env_cdsgroup_begin.html">DB_ENV->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.
</ul>
<br>
<br><b>Errors</b>
<p>The DB->get method
may fail and return one of the following non-zero errors:</p>
<br>
<b>DB_BUFFER_SMALL</b><ul compact><li>The requested item could not be returned due to undersized buffer.</ul>
<br>
<br>
<b>DB_LOCK_DEADLOCK</b><ul compact><li>A transactional database environment operation was selected to resolve
a deadlock.</ul>
<b>DB_LOCK_NOTGRANTED</b><ul compact><li>A Berkeley DB Concurrent Data Store database environment configured for lock timeouts was unable
to grant a lock in the allowed time.</ul>
<br>
<br>
<b>DB_LOCK_NOTGRANTED</b><ul compact><li>The DB_CONSUME_WAIT flag was specified, lock or transaction
timers were configured and the lock could not be granted before the wait-time expired.</ul>
<br>
<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_LEASE_EXPIRED</b><ul compact><li>The operation failed because the site's replication master lease has expired.</ul>
<br>
<br>
<b>DB_REP_LOCKOUT</b><ul compact><li>The operation was blocked by client/master synchronization.</ul>
<br>
<br>
<b>DB_SECONDARY_BAD</b><ul compact><li>A secondary index references a nonexistent primary key.</ul>
<br>
<br>
<b>EINVAL</b><ul compact><li>If a record number of 0 was specified;
the <a href="../../db4-devel-4.7.25/api_c/env_open.html#DB_THREAD">DB_THREAD</a> flag was specified to the <a href="../../db4-devel-4.7.25/api_c/db_open.html">DB->open</a> method and
none of the <a href="../../db4-devel-4.7.25/api_c/dbt_class.html#DB_DBT_MALLOC">DB_DBT_MALLOC</a>, <a href="../../db4-devel-4.7.25/api_c/dbt_class.html#DB_DBT_REALLOC">DB_DBT_REALLOC</a> or
<a href="../../db4-devel-4.7.25/api_c/dbt_class.html#DB_DBT_USERMEM">DB_DBT_USERMEM</a> flags were set in the <a href="../../db4-devel-4.7.25/api_c/dbt_class.html">DBT</a>;
the DB->pget method was called with a <a href="../../db4-devel-4.7.25/api_c/db_class.html">DB</a> handle that does not
refer to a secondary index; or if an
invalid flag value or parameter was specified.</ul>
<br>
<hr size=1 noshade>
<br><b>Class</b>
<a href="../../db4-devel-4.7.25/api_c/db_class.html">DB</a>
<br><b>See Also</b>
<a href="../../db4-devel-4.7.25/api_c/db_list.html">Databases and Related Methods</a>
</tt>
<table width="100%"><tr><td><br></td><td align=right>
<a href="../../db4-devel-4.7.25/api_c/api_core.html"><img src="../../db4-devel-4.7.25/images/api.gif" alt="API"></a><a href="../../db4-devel-4.7.25/ref/toc.html"><img src="../../db4-devel-4.7.25/images/ref.gif" alt="Ref"></a>
</td></tr></table>
<p><font size=1>Copyright (c) 1996,2008 Oracle. All rights reserved.</font>
</body>
</html>
Copyright 2K16 - 2K18 Indonesian Hacker Rulez
;?>)