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berkdb env
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<pre>berkdb env
	[-cachesize {gbytes bytes ncache}]
	[-create]
	[-data_dir dirname]
	[-encryptaes passwd]
	[-encryptany passwd]
	[-errfile filename]
	[-home directory]
	[-log_dir dirname]
	[-mode mode]
	[-private]
	[-recover]
	[-recover_fatal]
	[-shm_key shmid]
	[-system_mem]
	[-tmp_dir dirname]
	[-txn [nosync]]
	[-txn_max max]
	[-use_environ]
	[-use_environ_root]
</pre>
Description(berkdb env)
The berkdb env command opens and optionally creates a database
environment. The returned environment handle is bound to a Tcl command
of the form envN, where N is an integer starting at 0 (for
example, env0 and env1). It is through this Tcl command that the script
accesses the environment methods. The command automatically initializes
the Shared Memory Buffer Pool subsystem. This subsystem is used
whenever the application is using any Berkeley DB access method.
The options are as follows:
 
-cachesize {gbytes bytes ncache}<ul compact><li>Set the size of the database's shared memory buffer pool (that is, the
cache), to gbytes gigabytes plus bytes. The cache
should be the size of the normal working data set of the application,
with some small amount of additional memory for unusual situations.
(Note: The working set is not the same as the number of simultaneously
referenced pages, and should be quite a bit larger!)
The default cache size is 256KB, and may not be specified as less than
20KB. Any cache size less than 500MB is automatically increased by 25%
to account for buffer pool overhead; cache sizes larger than 500MB are
used as specified.
It is possible to specify caches to Berkeley DB that are large enough so that
they cannot be allocated contiguously on some architectures; for example,
some releases of Solaris limit the amount of memory that may be
allocated contiguously by a process. If ncache is 0 or 1, the
cache will be allocated contiguously in memory. If it is greater than
1, the cache will be broken up into ncache equally sized
separate pieces of memory.
For information on tuning the Berkeley DB cache size, see
<a href="../../db4-devel-4.7.25/ref/am_conf/cachesize.html">Selecting a cache size</a>.</ul>
-create<ul compact><li>Cause Berkeley DB subsystems to create any underlying files, as necessary.</ul>
-data_dir dirname<ul compact><li>Specify the environment's data directory as described in
<a href="../../db4-devel-4.7.25/ref/env/naming.html">Berkeley DB File Naming</a>.</ul>
-encryptaes passwd<ul compact><li>Specify the database should be encrypted with the given password
using the Rijndael/AES (also known as the Advanced Encryption Standard
and Federal Information Processing Standard (FIPS) 197) algorithm.</ul>
-encryptany passwd<ul compact><li>Specify the already existing environment should be opened
with the given password. This option is used if the environment is
known to be encrypted, but the specific algorithm used is not known.</ul>
-errfile filename<ul compact><li>When an error occurs in the Berkeley DB library, a Berkeley DB error or an error
return value is returned by the function. In some cases, however, the
errno value may be insufficient to completely describe the cause of the
error especially during initial application debugging.
The -errfile argument is used to enhance the mechanism for
reporting error messages to the application by specifying a file to be
used for displaying additional Berkeley DB error messages. In some cases, when
an error occurs, Berkeley DB will output an additional error message to the
specified file reference.
consist of the environment command name (for example, env0) and a colon
(":"), an error string, and a trailing &lt;newline&gt;
character.
This error-logging enhancement does not slow performance or significantly
increase application size, and may be run during normal operation as well
as during application debugging.</ul>
-home directory<ul compact><li>The -home argument is described in
<a href="../../db4-devel-4.7.25/ref/env/naming.html">Berkeley DB File Naming</a>.</ul>
-log_dir dirname<ul compact><li>Specify the environment's logging file directory as described in
<a href="../../db4-devel-4.7.25/ref/env/naming.html">Berkeley DB File Naming</a>.</ul>
-mode mode<ul compact><li>On UNIX systems, or in IEEE/ANSI Std 1003.1 (POSIX) environments, all files created by Berkeley DB
are created with mode mode (as described in chmod(2)) and
modified by the process' umask value at the time of creation (see
umask(2)). The group ownership of created files is based on
the system and directory defaults, and is not further specified by Berkeley DB.
If mode is 0, files are created readable and writable by both
owner and group. On Windows systems, the mode argument is ignored.</ul>
-private<ul compact><li>Specify that the environment will only be accessed by a single process
(although that process may be multithreaded). 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.
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. For example, if both a server application
and the Berkeley DB utility <a href="../../db4-utils-4.7.25/utility/db_stat.html">db_stat</a> will access the environment, the
-private option should not be specified.</ul>
-recover<ul compact><li>Run normal recovery on this environment before opening it for normal use.
If this flag is set, the -create option must also be set because
the regions will be removed and re-created.</ul>
-recover_fatal<ul compact><li>Run catastrophic recovery on this environment before opening it for
normal use. If this flag is set, the -create option must also be
set since the regions will be removed and re-created.</ul>
-shm_key key<ul compact><li>Specify a base segment ID for Berkeley DB environment shared memory regions
created in system memory on systems supporting X/Open-style shared
memory interfaces, for example, UNIX systems supporting shmget(2) and
related System V IPC interfaces. See <a href="../../db4-devel-4.7.25/ref/env/region.html">Shared Memory Regions</a> for more information.</ul>
-system_mem<ul compact><li>Allocate memory from system shared memory instead of memory backed by the
filesystem. See <a href="../../db4-devel-4.7.25/ref/env/region.html">Shared Memory Regions</a>
for more information.</ul>
-tmp_dir dirname<ul compact><li>Specify the environment's tmp directory, as described in
<a href="../../db4-devel-4.7.25/ref/env/naming.html">Berkeley DB File Naming</a>.</ul>
-txn [nosync]<ul compact><li>Initialize the Transaction subsystem. This subsystem is used when
recovery and atomicity of multiple operations and recovery are important.
The -txn option implies the initialization of the logging
and locking subsystems as well.
If the optional nosync argument is specified, the log will not
be synchronously flushed on transaction commit. This means that
transactions exhibit the ACI (atomicity, consistency, and isolation)
properties, but not D (durability); that is, database integrity will be
maintained, but it is possible that some number of the most recently
committed transactions may be undone during recovery instead of being
redone.
The number of transactions that are potentially at risk is governed by
how often the log is checkpointed (see <a href="../../db4-utils-4.7.25/utility/db_checkpoint.html">db_checkpoint</a> for more
information) and how many log updates can fit on a single log page.</ul>
-txn_max max<ul compact><li>Set the maximum number of simultaneous transactions that are supported
by the environment, which bounds the size of backing files. When there
are more than the specified number of concurrent transactions, calls to
env txn will fail (until some active transactions complete).</ul>
-use_environ<ul compact><li>The Berkeley DB process' environment may be permitted to specify information
to be used when naming files; see
<a href="../../db4-devel-4.7.25/ref/env/naming.html">Berkeley DB File Naming</a>.
Because 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 -use_environ flag is set.</ul>
-use_environ_root<ul compact><li>The Berkeley DB process' environment may be permitted to specify information
to be used when naming files; see
<a href="../../db4-devel-4.7.25/ref/env/naming.html">Berkeley DB File Naming</a>.
As permitting users to specify which files are used can create security
problems, if the -use_environ_root flag is set, environment
information will be used for file naming only for users with appropriate
permissions (for example, users with a user-ID of 0 on IEEE/ANSI Std 1003.1 (POSIX)
systems).</ul>
 
The berkdb env command returns an environment handle on success.
In the case of error, a Tcl error is thrown.
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