1<!--$Id: env_open.so,v 11.29 2002/12/22 21:11:07 bostic Exp $--> 2<!--$Id: m4.tcl,v 11.28 2004/12/16 19:13:05 bostic Exp $--> 3<!--Copyright (c) 1997,2008 Oracle. All rights reserved.--> 4<!--See the file LICENSE for redistribution information.--> 5<html> 6<head> 7<title>Berkeley DB: berkdb env</title> 8<meta name="description" content="Berkeley DB: An embedded database programmatic toolkit."> 9<meta name="keywords" content="embedded,database,programmatic,toolkit,btree,hash,hashing,transaction,transactions,locking,logging,access method,access methods,Java,C,C++"> 10</head> 11<body bgcolor=white> 12<table width="100%"><tr valign=top> 13<td> 14<b><b>berkdb env</b></b> 15</td> 16<td align=right> 17<a href="../api_tcl/api_tcl.html"><img src="../images/api.gif" alt="API"></a> 18<a href="../ref/toc.html"><img src="../images/ref.gif" alt="Ref"></a></td> 19</tr></table> 20<hr size=1 noshade> 21<tt> 22<b><pre>berkdb env 23 [-cachesize {gbytes bytes ncache}] 24 [-create] 25 [-data_dir dirname] 26 [-encryptaes passwd] 27 [-encryptany passwd] 28 [-errfile filename] 29 [-home directory] 30 [-log_dir dirname] 31 [-mode mode] 32 [-private] 33 [-recover] 34 [-recover_fatal] 35 [-shm_key shmid] 36 [-system_mem] 37 [-tmp_dir dirname] 38 [-txn [nosync]] 39 [-txn_max max] 40 [-use_environ] 41 [-use_environ_root] 42</pre></b> 43<b>Description(berkdb env)</b> 44<p>The <b>berkdb env</b> command opens and optionally creates a database 45environment. The returned environment handle is bound to a Tcl command 46of the form <b>envN</b>, where N is an integer starting at 0 (for 47example, env0 and env1). It is through this Tcl command that the script 48accesses the environment methods. The command automatically initializes 49the Shared Memory Buffer Pool subsystem. This subsystem is used 50whenever the application is using any Berkeley DB access method.</p> 51<p>The options are as follows:</p> 52<br> 53<b>-cachesize {gbytes bytes ncache}</b><ul compact><li>Set the size of the database's shared memory buffer pool (that is, the 54cache), to <b>gbytes</b> gigabytes plus <b>bytes</b>. The cache 55should be the size of the normal working data set of the application, 56with some small amount of additional memory for unusual situations. 57(Note: The working set is not the same as the number of simultaneously 58referenced pages, and should be quite a bit larger!) 59<p>The default cache size is 256KB, and may not be specified as less than 6020KB. Any cache size less than 500MB is automatically increased by 25% 61to account for buffer pool overhead; cache sizes larger than 500MB are 62used as specified.</p> 63<p>It is possible to specify caches to Berkeley DB that are large enough so that 64they cannot be allocated contiguously on some architectures; for example, 65some releases of Solaris limit the amount of memory that may be 66allocated contiguously by a process. If <b>ncache</b> is 0 or 1, the 67cache will be allocated contiguously in memory. If it is greater than 681, the cache will be broken up into <b>ncache</b> equally sized 69separate pieces of memory.</p> 70<p>For information on tuning the Berkeley DB cache size, see 71<a href="../ref/am_conf/cachesize.html">Selecting a cache size</a>.</p></ul> 72<b>-create</b><ul compact><li>Cause Berkeley DB subsystems to create any underlying files, as necessary.</ul> 73<b>-data_dir dirname</b><ul compact><li>Specify the environment's data directory as described in 74<a href="../ref/env/naming.html">Berkeley DB File Naming</a>.</ul> 75<b>-encryptaes passwd</b><ul compact><li>Specify the database should be encrypted with the given password 76using the Rijndael/AES (also known as the Advanced Encryption Standard 77and Federal Information Processing Standard (FIPS) 197) algorithm.</ul> 78<b>-encryptany passwd</b><ul compact><li>Specify the already existing environment should be opened 79with the given password. This option is used if the environment is 80known to be encrypted, but the specific algorithm used is not known.</ul> 81<b>-errfile filename</b><ul compact><li><p>When an error occurs in the Berkeley DB library, a Berkeley DB error or an error 82return value is returned by the function. In some cases, however, the 83errno value may be insufficient to completely describe the cause of the 84error especially during initial application debugging.</p> 85<p>The <b>-errfile</b> argument is used to enhance the mechanism for 86reporting error messages to the application by specifying a file to be 87used for displaying additional Berkeley DB error messages. In some cases, when 88an error occurs, Berkeley DB will output an additional error message to the 89specified file reference.</p> 90<p>consist of the environment command name (for example, env0) and a colon 91(":"), an error string, and a trailing <newline> 92character.</p> 93<p>This error-logging enhancement does not slow performance or significantly 94increase application size, and may be run during normal operation as well 95as during application debugging.</p></ul> 96<b>-home directory</b><ul compact><li>The <b>-home</b> argument is described in 97<a href="../ref/env/naming.html">Berkeley DB File Naming</a>.</ul> 98<b>-log_dir dirname</b><ul compact><li>Specify the environment's logging file directory as described in 99<a href="../ref/env/naming.html">Berkeley DB File Naming</a>.</ul> 100<b>-mode mode</b><ul compact><li><p>On UNIX systems, or in IEEE/ANSI Std 1003.1 (POSIX) environments, all files created by Berkeley DB 101are created with mode <b>mode</b> (as described in <b>chmod</b>(2)) and 102modified by the process' umask value at the time of creation (see 103<b>umask</b>(2)). The group ownership of created files is based on 104the system and directory defaults, and is not further specified by Berkeley DB. 105If <b>mode</b> is 0, files are created readable and writable by both 106owner and group. On Windows systems, the mode argument is ignored.</p></ul> 107<b>-private</b><ul compact><li>Specify that the environment will only be accessed by a single process 108(although that process may be multithreaded). This flag has two effects 109on the Berkeley DB environment. First, all underlying data structures are 110allocated from per-process memory instead of from shared memory that is 111potentially accessible to more than a single process. Second, mutexes 112are only configured to work between threads. 113<p>This flag should not be specified if more than a single process is 114accessing the environment, as it is likely to cause database corruption 115and unpredictable behavior. For example, if both a server application 116and the Berkeley DB utility <a href="../utility/db_stat.html">db_stat</a> will access the environment, the 117<b>-private</b> option should not be specified.</p></ul> 118<b>-recover</b><ul compact><li>Run normal recovery on this environment before opening it for normal use. 119If this flag is set, the <b>-create</b> option must also be set because 120the regions will be removed and re-created.</ul> 121<b>-recover_fatal</b><ul compact><li>Run catastrophic recovery on this environment before opening it for 122normal use. If this flag is set, the <b>-create</b> option must also be 123set since the regions will be removed and re-created.</ul> 124<b>-shm_key key</b><ul compact><li>Specify a base segment ID for Berkeley DB environment shared memory regions 125created in system memory on systems supporting X/Open-style shared 126memory interfaces, for example, UNIX systems supporting shmget(2) and 127related System V IPC interfaces. See <a href="../ref/env/region.html">Shared Memory Regions</a> for more information.</ul> 128<b>-system_mem</b><ul compact><li>Allocate memory from system shared memory instead of memory backed by the 129filesystem. See <a href="../ref/env/region.html">Shared Memory Regions</a> 130for more information.</ul> 131<b>-tmp_dir dirname</b><ul compact><li>Specify the environment's tmp directory, as described in 132<a href="../ref/env/naming.html">Berkeley DB File Naming</a>.</ul> 133<b>-txn [nosync]</b><ul compact><li>Initialize the Transaction subsystem. This subsystem is used when 134recovery and atomicity of multiple operations and recovery are important. 135The <b>-txn</b> option implies the initialization of the logging 136and locking subsystems as well. 137<p>If the optional <b>nosync</b> argument is specified, the log will not 138be synchronously flushed on transaction commit. This means that 139transactions exhibit the ACI (atomicity, consistency, and isolation) 140properties, but not D (durability); that is, database integrity will be 141maintained, but it is possible that some number of the most recently 142committed transactions may be undone during recovery instead of being 143redone.</p> 144<p>The number of transactions that are potentially at risk is governed by 145how often the log is checkpointed (see <a href="../utility/db_checkpoint.html">db_checkpoint</a> for more 146information) and how many log updates can fit on a single log page.</p></ul> 147<b>-txn_max max</b><ul compact><li>Set the maximum number of simultaneous transactions that are supported 148by the environment, which bounds the size of backing files. When there 149are more than the specified number of concurrent transactions, calls to 150<i>env</i> <b>txn</b> will fail (until some active transactions complete).</ul> 151<b>-use_environ</b><ul compact><li>The Berkeley DB process' environment may be permitted to specify information 152to be used when naming files; see 153<a href="../ref/env/naming.html">Berkeley DB File Naming</a>. 154Because permitting users to specify which files are used can create 155security problems, environment information will be used in file naming 156for all users only if the <b>-use_environ</b> flag is set.</ul> 157<b>-use_environ_root</b><ul compact><li>The Berkeley DB process' environment may be permitted to specify information 158to be used when naming files; see 159<a href="../ref/env/naming.html">Berkeley DB File Naming</a>. 160As permitting users to specify which files are used can create security 161problems, if the <b>-use_environ_root</b> flag is set, environment 162information will be used for file naming only for users with appropriate 163permissions (for example, users with a user-ID of 0 on IEEE/ANSI Std 1003.1 (POSIX) 164systems).</ul> 165<br> 166<p>The <b>berkdb env</b> command returns an environment handle on success.</p> 167<p>In the case of error, a Tcl error is thrown.</p> 168</tt> 169<table width="100%"><tr><td><br></td><td align=right> 170<a href="../api_tcl/api_tcl.html"><img src="../images/api.gif" alt="API"></a><a href="../ref/toc.html"><img src="../images/ref.gif" alt="Ref"></a> 171</td></tr></table> 172<p><font size=1>Copyright (c) 1996,2008 Oracle. All rights reserved.</font> 173</body> 174</html> 175