mirror of
https://github.com/MariaDB/server.git
synced 2025-08-09 22:24:09 +03:00
206 lines
12 KiB
HTML
206 lines
12 KiB
HTML
<!--$Id: env_open.so,v 10.61 2000/12/01 15:50:31 bostic Exp $-->
|
|
<!--Copyright 1997, 1998, 1999, 2000 by Sleepycat Software, Inc.-->
|
|
<!--All rights reserved.-->
|
|
<html>
|
|
<head>
|
|
<title>Berkeley DB: DBENV->open</title>
|
|
<meta name="description" content="Berkeley DB: An embedded database programmatic toolkit.">
|
|
<meta name="keywords" content="embedded,database,programmatic,toolkit,b+tree,btree,hash,hashing,transaction,transactions,locking,logging,access method,access methods,java,C,C++">
|
|
</head>
|
|
<body bgcolor=white>
|
|
<a name="2"><!--meow--></a>
|
|
<table><tr valign=top>
|
|
<td>
|
|
<h1>DBENV->open</h1>
|
|
</td>
|
|
<td width="1%">
|
|
<a href="../api_c/c_index.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>
|
|
<h3><pre>
|
|
#include <db.h>
|
|
<p>
|
|
int
|
|
DBENV->open(DB_ENV *, char *db_home, u_int32_t flags, int mode);
|
|
</pre></h3>
|
|
<h1>Description</h1>
|
|
<p>The DBENV->open function is the interface for opening the Berkeley DB
|
|
environment. It provides a structure for creating a consistent
|
|
environment for processes using one or more of the features of Berkeley DB.
|
|
<p>The <b>db_home</b> argument to DBENV->open (and file name
|
|
resolution in general) is described in
|
|
<a href="../ref/env/naming.html">Berkeley DB File Naming</a>.
|
|
<p>The <b>flags</b> argument specifies the subsystems that are initialized
|
|
and how the application's environment affects Berkeley DB file naming, among
|
|
other things.
|
|
<p>The <b>flags</b> value must be set to 0 or by bitwise inclusively <b>OR</b>'ing together one or more
|
|
of the following values.
|
|
<p>As there are a large number of flags that can be specified, they have been
|
|
grouped together by functionality. The first group of flags indicate
|
|
which of the Berkeley DB subsystems should be initialized:
|
|
<p><dl compact>
|
|
<p><dt><a name="DB_JOINENV">DB_JOINENV</a><dd>Join an existing environment. This option allows applications to
|
|
join an existing environment without knowing which Berkeley DB subsystems
|
|
the environment supports.
|
|
<p><dt><a name="DB_INIT_CDB">DB_INIT_CDB</a><dd>Initialize locking for the <a href="../ref/cam/intro.html">Berkeley DB Concurrent Data Store</a>
|
|
product. In this mode, Berkeley DB provides multiple reader/single writer
|
|
access. The only other subsystem that should be specified with the
|
|
DB_INIT_CDB flag is DB_INIT_MPOOL.
|
|
<p>Access method calls are largely unchanged when using this flag, although
|
|
any cursors through which update operations (e.g., <a href="../api_c/dbc_put.html">DBcursor->c_put</a>,
|
|
<a href="../api_c/dbc_del.html">DBcursor->c_del</a>) will be made must have the <a href="../api_c/db_cursor.html#DB_WRITECURSOR">DB_WRITECURSOR</a> value
|
|
set in the flags parameter to the cursor call that creates the cursor.
|
|
See <a href="../api_c/db_cursor.html">DB->cursor</a> for more information.
|
|
<p><dt><a name="DB_INIT_LOCK">DB_INIT_LOCK</a><dd>Initialize the locking subsystem. This subsystem should be used when
|
|
multiple processes or threads are going to be reading and writing a Berkeley DB
|
|
database, so that they do not interfere with each other. If all threads
|
|
are accessing the database(s) read-only, then locking is unnecessary.
|
|
When the DB_INIT_LOCK flag is specified, it is usually necessary to run
|
|
the deadlock detector, as well. See <a href="../utility/db_deadlock.html">db_deadlock</a> and
|
|
<a href="../api_c/lock_detect.html">lock_detect</a> for more information.
|
|
<p><dt><a name="DB_INIT_LOG">DB_INIT_LOG</a><dd>Initialize the logging subsystem. This subsystem is used when recovery
|
|
from application or system failure is necessary.
|
|
<p>The log is stored in one or more files in the environment directory.
|
|
Each file is named using the format <i>log.NNNNNNNNNN</i>, where
|
|
<i>NNNNNNNNNN</i> is the sequence number of the file within the log.
|
|
For further information, see
|
|
<a href="../ref/log/limits.html">Log File Limits</a>.
|
|
<p>If the log region is being created and log files are already present, the
|
|
log files are reviewed and subsequent log writes are appended
|
|
to the end of the log, rather than overwriting current log entries.
|
|
<p><dt><a name="DB_INIT_MPOOL">DB_INIT_MPOOL</a><dd>Initialize the shared memory buffer pool subsystem. This subsystem is
|
|
used whenever the application is using any Berkeley DB access method.
|
|
<p><dt><a name="DB_INIT_TXN">DB_INIT_TXN</a><dd>Initialize the transaction subsystem. This subsystem is used when
|
|
recovery and atomicity of multiple operations and recovery are important.
|
|
The DB_INIT_TXN flag implies the DB_INIT_LOG flag.
|
|
</dl>
|
|
<p>The second group of flags govern what recovery, if any, is performed when
|
|
the environment is initialized:
|
|
<p><dl compact>
|
|
<p><dt><a name="DB_RECOVER">DB_RECOVER</a><dd>Run normal recovery on this environment before opening it for normal use.
|
|
If this flag is set, the DB_CREATE flag must also be set since the regions
|
|
will be removed and recreated.
|
|
<p><dt><a name="DB_RECOVER_FATAL">DB_RECOVER_FATAL</a><dd>Run catastrophic recovery on this environment before opening it for normal
|
|
use. If this flag is set, the DB_CREATE flag must also be set since the
|
|
regions will be removed and recreated.
|
|
</dl>
|
|
<p>A standard part of the recovery process is to remove the existing Berkeley DB
|
|
environment and create a new one in which to perform recovery. If the
|
|
thread of control performing recovery does not specify the correct region
|
|
initialization information (e.g., the correct memory pool cache size),
|
|
the result can be an application running in an environment with incorrect
|
|
cache and other subsystem sizes. For this reason, the thread of control
|
|
performing recovery should either specify correct configuration
|
|
information before calling the DBENV->open function, or it should remove
|
|
the environment after recovery is completed, leaving creation of the
|
|
correctly sized environment to a subsequent call to DBENV->open.
|
|
<p>All Berkeley DB recovery processing must be single-threaded, that is, only a
|
|
single thread of control may perform recovery or access a Berkeley DB
|
|
environment while recovery is being performed. As it is not an error to
|
|
specify DB_RECOVER for an environment for which no recovery is
|
|
required, it is reasonable programming practice for the thread of control
|
|
responsible for performing recovery and creating the environment to always
|
|
specify the DB_RECOVER flag during startup.
|
|
<p>The DBENV->open function returns successfully if DB_RECOVER
|
|
or DB_RECOVER_FATAL is specified and no log files exist, so it is
|
|
necessary to ensure all necessary log files are present before running
|
|
recovery. For further information, consult <a href="../utility/db_archive.html">db_archive</a> and
|
|
<a href="../utility/db_recover.html">db_recover</a>.
|
|
<p>The third group of flags govern file naming extensions in the environment:
|
|
<p><dl compact>
|
|
<!--$Id: m4.env_flags,v 10.9 2000/06/29 22:54:10 bostic Exp $-->
|
|
<p><dt><a name="DB_USE_ENVIRON">DB_USE_ENVIRON</a><dd>The Berkeley DB process' environment may be permitted to specify information to
|
|
be used when naming files; see <a href="../ref/env/naming.html">Berkeley DB
|
|
File Naming</a>. As permitting users to specify which files are used can
|
|
create security problems, environment information will be used in file
|
|
naming for all users only if the DB_USE_ENVIRON flag is set.
|
|
<p><dt><a name="DB_USE_ENVIRON_ROOT">DB_USE_ENVIRON_ROOT</a><dd>The Berkeley DB process' environment may be permitted to specify information to
|
|
be used when naming files; see <a href="../ref/env/naming.html">Berkeley DB
|
|
File Naming</a>. As permitting users to specify which files are used can
|
|
create security problems, if the DB_USE_ENVIRON_ROOT flag is set,
|
|
environment information will be used for file naming only for users with
|
|
appropriate permissions (e.g., on UNIX systems, users with a user-ID of 0).
|
|
</dl>
|
|
<p>Finally, there are a few additional, unrelated flags:
|
|
<p><dl compact>
|
|
<p><dt><a name="DB_CREATE">DB_CREATE</a><dd>Cause Berkeley DB subsystems to create any underlying files, as necessary.
|
|
<p><dt><a name="DB_LOCKDOWN">DB_LOCKDOWN</a><dd>Lock shared Berkeley DB environment files and memory mapped databases into memory.
|
|
<p><dt><a name="DB_PRIVATE">DB_PRIVATE</a><dd>Specify that the environment will only be accessed by a single process
|
|
(although that process may be multi-threaded). This flag has two effects
|
|
on the Berkeley DB environment. First, all underlying data structures are
|
|
allocated from per-process memory instead of from shared memory that is
|
|
potentially accessible to more than a single process. Second, mutexes
|
|
are only configured to work between threads.
|
|
<p>This flag should not be specified if more than a single process is
|
|
accessing the environment, as it is likely to cause database corruption
|
|
and unpredictable behavior, e.g., if both a server application and the
|
|
Berkeley DB utility <a href="../utility/db_stat.html">db_stat</a> will access the environment, the
|
|
DB_PRIVATE flag should not be specified.
|
|
<p><dt><a name="DB_SYSTEM_MEM">DB_SYSTEM_MEM</a><dd>Allocate memory from system shared memory instead of from memory backed
|
|
by the filesystem. See <a href="../ref/env/region.html">Shared Memory
|
|
Regions</a> for more information.
|
|
<p><dt><a name="DB_THREAD">DB_THREAD</a><dd>Cause the DB_ENV handle returned by DBENV->open to be
|
|
<i>free-threaded</i>, that is, useable by multiple threads within a
|
|
single address space.
|
|
</dl>
|
|
<p>On UNIX systems, or in IEEE/ANSI Std 1003.1 (POSIX) environments, all files created by Berkeley DB
|
|
are created with mode <b>mode</b> (as described in <b>chmod</b>(2)) and
|
|
modified by the process' umask value at the time of creation (see
|
|
<b>umask</b>(2)). The group ownership of created files is based on
|
|
the system and directory defaults, and is not further specified by Berkeley DB.
|
|
If <b>mode</b> is 0, files are created readable and writeable by both
|
|
owner and group. On Windows systems, the mode argument is ignored.
|
|
<p>The DBENV->open function returns a non-zero error value on failure and 0 on success.
|
|
<h1>Environment Variables</h1>
|
|
<p><dl compact>
|
|
<p><dt>DB_HOME<dd>The environment variable <b>DB_HOME</b> may be used as the path of
|
|
the database home as described in
|
|
<a href="../ref/env/naming.html">Berkeley DB File Naming</a>.
|
|
</dl>
|
|
<h1>Errors</h1>
|
|
<p>The DBENV->open function may fail and return a non-zero error for the following conditions:
|
|
<p><dl compact>
|
|
<p><dt>EAGAIN<dd>The shared memory region was locked and (repeatedly) unavailable.
|
|
</dl>
|
|
<p><dl compact>
|
|
<p><dt>EINVAL<dd>An invalid flag value or parameter was specified.
|
|
<p>
|
|
The DB_THREAD flag was specified and spinlocks are not
|
|
implemented for this architecture.
|
|
<p>The DB_HOME or TMPDIR environment variables were set but empty.
|
|
<p>An incorrectly formatted <b>NAME VALUE</b> entry or line was found.
|
|
</dl>
|
|
<p><dl compact>
|
|
<p><dt>ENOSPC<dd>HP-UX only: a previously created Berkeley DB environment for this process still
|
|
exists.
|
|
</dl>
|
|
<p>The DBENV->open function may fail and return a non-zero error for errors specified for other Berkeley DB and C library or system functions.
|
|
If a catastrophic error has occurred, the DBENV->open function may fail and return
|
|
<a href="../ref/program/errorret.html#DB_RUNRECOVERY">DB_RUNRECOVERY</a>, in which case all subsequent Berkeley DB calls will fail
|
|
in the same way.
|
|
<h1>See Also</h1>
|
|
<a href="../api_c/env_close.html">DBENV->close</a>,
|
|
<a href="../api_c/env_create.html">db_env_create</a>,
|
|
<a href="../api_c/env_open.html">DBENV->open</a>,
|
|
<a href="../api_c/env_remove.html">DBENV->remove</a>,
|
|
<a href="../api_c/db_err.html">DBENV->err</a>,
|
|
<a href="../api_c/env_strerror.html">db_strerror</a>,
|
|
<a href="../api_c/env_version.html">db_version</a>,
|
|
<a href="../api_c/env_set_cachesize.html">DBENV->set_cachesize</a>,
|
|
<a href="../api_c/env_set_errcall.html">DBENV->set_errcall</a>,
|
|
<a href="../api_c/env_set_errfile.html">DBENV->set_errfile</a>,
|
|
<a href="../api_c/env_set_errpfx.html">DBENV->set_errpfx</a>,
|
|
<a href="../api_c/env_set_flags.html">DBENV->set_flags</a>,
|
|
<a href="../api_c/env_set_mutexlocks.html">DBENV->set_mutexlocks</a>,
|
|
<a href="../api_c/env_set_paniccall.html">DBENV->set_paniccall</a>,
|
|
and
|
|
<a href="../api_c/env_set_verbose.html">DBENV->set_verbose</a>.
|
|
</tt>
|
|
<table><tr><td><br></td><td width="1%">
|
|
<a href="../api_c/c_index.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><a href="http://www.sleepycat.com">Copyright Sleepycat Software</a></font>
|
|
</body>
|
|
</html>
|