1<?xml version="1.0" encoding="UTF-8" standalone="no"?> 2<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> 3<html xmlns="http://www.w3.org/1999/xhtml"> 4 <head> 5 <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /> 6 <title>berkdb env</title> 7 <link rel="stylesheet" href="apiReference.css" type="text/css" /> 8 <meta name="generator" content="DocBook XSL Stylesheets V1.73.2" /> 9 <link rel="start" href="index.html" title="Berkeley DB TCL API Reference" /> 10 <link rel="up" href="tclapi.html" title="Chapter��1.�� Berkeley DB Tcl APIs" /> 11 <link rel="prev" href="env_dbrename.html" title="env dbrename" /> 12 <link rel="next" href="env_remove.html" title="berkdb envremove" /> 13 </head> 14 <body> 15 <div class="navheader"> 16 <table width="100%" summary="Navigation header"> 17 <tr> 18 <th colspan="3" align="center">berkdb env</th> 19 </tr> 20 <tr> 21 <td width="20%" align="left"><a accesskey="p" href="env_dbrename.html">Prev</a>��</td> 22 <th width="60%" align="center">Chapter��1.�� 23 Berkeley DB Tcl APIs 24 </th> 25 <td width="20%" align="right">��<a accesskey="n" href="env_remove.html">Next</a></td> 26 </tr> 27 </table> 28 <hr /> 29 </div> 30 <div class="sect1" lang="en" xml:lang="en"> 31 <div class="titlepage"> 32 <div> 33 <div> 34 <h2 class="title" style="clear: both"><a id="env_open"></a>berkdb env</h2> 35 </div> 36 </div> 37 </div> 38 <pre class="programlisting">berkdb env 39 [-cachesize {gbytes bytes ncache}] 40 [-create] 41 [-data_dir dirname] 42 [-encryptaes passwd] 43 [-encryptany passwd] 44 [-errfile filename] 45 [-home directory] 46 [-log_dir dirname] 47 [-mode mode] 48 [-private] 49 [-recover] 50 [-recover_fatal] 51 [-shm_key shmid] 52 [-system_mem] 53 [-tmp_dir dirname] 54 [-txn [nosync]] 55 [-txn_max max] 56 [-use_environ] 57 [-use_environ_root] </pre> 58 <p> 59 The <span class="bold"><strong>berkdb env</strong></span> command opens and 60 optionally creates a database environment. The returned environment 61 handle is bound to a Tcl command of the form <span class="bold"><strong>envN</strong></span>, where N is an integer starting at 0 (for 62 example, env0 and env1). It is through this Tcl command that the 63 script accesses the environment methods. The command automatically 64 initializes the Shared Memory Buffer Pool subsystem. This subsystem 65 is used whenever the application is using any Berkeley DB access 66 method. 67 </p> 68 <p> 69 The options are as follows: 70 </p> 71 <div class="itemizedlist"> 72 <ul type="disc"> 73 <li> 74 <p> 75 <span class="bold"><strong>-cachesize {gbytes bytes ncache}</strong></span> 76 </p> 77 <p> 78 Set the size of the database's shared memory buffer pool (that is, the 79 cache), to <span class="bold"><strong>gbytes</strong></span> gigabytes plus 80 <span class="bold"><strong>bytes</strong></span>. The cache should be the size 81 of the normal working data set of the application, with some small 82 amount of additional memory for unusual situations. (Note: The working 83 set is not the same as the number of simultaneously referenced pages, 84 and should be quite a bit larger!) 85 </p> 86 <p> 87 The default cache size is 256KB, and may not be specified as less than 88 20KB. Any cache size less than 500MB is automatically increased by 89 25% to account for buffer pool overhead; cache sizes larger than 500MB 90 are used as specified. 91 </p> 92 <p> 93 It is possible to specify caches to Berkeley DB that are large enough 94 so that they cannot be allocated contiguously on some architectures; 95 for example, some releases of Solaris limit the amount of memory that 96 may be allocated contiguously by a process. If <span class="bold"><strong>ncache</strong></span> is 0 or 1, the cache will be allocated 97 contiguously in memory. If it is greater than 1, the cache will be 98 broken up into <span class="bold"><strong>ncache</strong></span> equally sized 99 separate pieces of memory. 100 </p> 101 <p> 102 For information on tuning the Berkeley DB cache size, see 103 <a href="../../programmer_reference/general_am_conf.html#am_conf_cachesize" class="olink">Selecting a Cache Size</a> 104 in the <em class="citetitle">Berkeley DB Programmer's Reference Guide</em>. 105 </p> 106 </li> 107 <li> 108 <p> 109 <span class="bold"><strong>-create</strong></span> 110 </p> 111 <p> 112 Cause Berkeley DB subsystems to create any underlying files, as 113 necessary. 114 </p> 115 </li> 116 <li> 117 <p> 118 <span class="bold"><strong>-data_dir dirname</strong></span> 119 </p> 120 <p> 121 Specify the environment's data directory as described in 122 <a href="../../programmer_reference/env_naming.html" class="olink">Berkeley DB File Naming</a> 123 in the <em class="citetitle">Berkeley DB Programmer's Reference Guide</em>. 124 </p> 125 </li> 126 <li> 127 <p> 128 <span class="bold"><strong>-encryptaes passwd</strong></span> 129 </p> 130 <p> 131 Specify the database should be encrypted with the given password using 132 the Rijndael/AES (also known as the Advanced Encryption Standard and 133 Federal Information Processing Standard (FIPS) 197) algorithm. 134 </p> 135 </li> 136 <li> 137 <p> 138 <span class="bold"><strong>-encryptany passwd</strong></span> 139 </p> 140 <p> 141 Specify the already existing environment should be opened with the 142 given password. This option is used if the environment is known to be 143 encrypted, but the specific algorithm used is not known. 144 </p> 145 </li> 146 <li> 147 <p> 148 <span class="bold"><strong>-errfile filename</strong></span> 149 </p> 150 <p> 151 When an error occurs in the Berkeley DB library, a Berkeley DB error 152 or an error return value is returned by the function. In some cases, 153 however, the errno value may be insufficient to completely describe 154 the cause of the error especially during initial application 155 debugging. 156 </p> 157 <p> 158 The <span class="bold"><strong>-errfile</strong></span> argument is used to 159 enhance the mechanism for reporting error messages to the application 160 by specifying a file to be used for displaying additional Berkeley DB 161 error messages. In some cases, when an error occurs, Berkeley DB will 162 output an additional error message to the specified file reference. 163 </p> 164 <p> 165 consist of the environment command name (for example, env0) and a 166 colon (":"), an error string, and a trailing <newline> 167 character. 168 </p> 169 <p> 170 This error-logging enhancement does not slow performance or 171 significantly increase application size, and may be run during normal 172 operation as well as during application debugging. 173 </p> 174 </li> 175 <li> 176 <p> 177 <span class="bold"><strong>-home directory</strong></span> 178 </p> 179 <p> 180 The <span class="bold"><strong>-home</strong></span> argument is described in 181 <a href="../../programmer_reference/env_naming.html" class="olink">Berkeley DB File Naming</a> 182 in the <em class="citetitle">Berkeley DB Programmer's Reference Guide</em>. 183 </p> 184 </li> 185 <li> 186 <p> 187 <span class="bold"><strong>-log_dir dirname</strong></span> 188 </p> 189 <p> 190 Specify the environment's logging file directory as described in 191 <a href="../../programmer_reference/env_naming.html" class="olink">Berkeley DB File Naming</a> 192 in the <em class="citetitle">Berkeley DB Programmer's Reference Guide</em>. 193 </p> 194 </li> 195 <li> 196 <p> 197 <span class="bold"><strong>-mode mode</strong></span> 198 </p> 199 <p> 200 On UNIX systems, or in IEEE/ANSI Std 1003.1 (POSIX) environments, all 201 files created by Berkeley DB are created with mode <span class="bold"><strong>mode</strong></span> (as described in <span class="bold"><strong>chmod</strong></span>(2)) and modified by the process' umask 202 value at the time of creation (see <span class="bold"><strong>umask</strong></span>(2)). The group ownership of created 203 files is based on the system and directory defaults, and is not 204 further specified by Berkeley DB. If <span class="bold"><strong>mode</strong></span> is 0, files are created readable and 205 writable by both owner and group. On Windows systems, the mode 206 argument is ignored. 207 </p> 208 </li> 209 <li> 210 <p> 211 <span class="bold"><strong>-private</strong></span> 212 </p> 213 <p> 214 Specify that the environment will only be accessed by a single process 215 (although that process may be multithreaded). This flag has two 216 effects on the Berkeley DB environment. First, all underlying data 217 structures are allocated from per-process memory instead of from 218 shared memory that is potentially accessible to more than a single 219 process. Second, mutexes are only configured to work between threads. 220 </p> 221 <p> 222 This flag should not be specified if more than a single process is 223 accessing the environment, as it is likely to cause database 224 corruption and unpredictable behavior. For example, if both a server 225 application and the Berkeley DB utility 226 <a href="../C/db_stat.html" class="olink">db_stat</a> 227 will access the environment, the <span class="bold"><strong>-private</strong></span> option 228 should not be specified. 229 </p> 230 </li> 231 <li> 232 <p> 233 <span class="bold"><strong>-recover</strong></span> 234 </p> 235 <p> 236 Run normal recovery on this environment before opening it for normal 237 use. If this flag is set, the <span class="bold"><strong>-create</strong></span> 238 option must also be set because the regions will be removed and 239 re-created. 240 </p> 241 </li> 242 <li> 243 <p> 244 <span class="bold"><strong>-recover_fatal</strong></span> 245 </p> 246 <p> 247 Run catastrophic recovery on this environment before opening it for 248 normal use. If this flag is set, the <span class="bold"><strong>-create</strong></span> option must also be set since the 249 regions will be removed and re-created. 250 </p> 251 </li> 252 <li> 253 <p> 254 <span class="bold"><strong>-shm_key key</strong></span> 255 </p> 256 <p> 257 Specify a base segment ID for Berkeley DB environment shared memory 258 regions created in system memory on systems supporting X/Open-style 259 shared memory interfaces, for example, UNIX systems supporting 260 shmget(2) and related System V IPC interfaces. See 261 <a href="../../programmer_reference/env_region.html" class="olink">Shared Memory Regions</a> 262 in the <em class="citetitle">Berkeley DB Programmer's Reference Guide</em> for more information. 263 </p> 264 </li> 265 <li> 266 <p> 267 <span class="bold"><strong>-system_mem</strong></span> 268 </p> 269 <p> 270 Allocate memory from system shared memory instead of memory backed by 271 the filesystem. See 272 <a href="../../programmer_reference/env_region.html" class="olink">Shared Memory Regions</a> 273 in the <em class="citetitle">Berkeley DB Programmer's Reference Guide</em> for more information. 274 </p> 275 </li> 276 <li> 277 <p> 278 <span class="bold"><strong>-tmp_dir dirname</strong></span> 279 </p> 280 <p> 281 Specify the environment's tmp directory, as described in 282 <a href="../../programmer_reference/env_naming.html" class="olink">Berkeley DB File Naming</a> 283 in the <em class="citetitle">Berkeley DB Programmer's Reference Guide</em>. 284 </p> 285 </li> 286 <li> 287 <p> 288 <span class="bold"><strong>-txn [nosync]</strong></span> 289 </p> 290 <p> 291 Initialize the Transaction subsystem. This subsystem is used when 292 recovery and atomicity of multiple operations and recovery are 293 important. The <span class="bold"><strong>-txn</strong></span> option implies 294 the initialization of the logging and locking subsystems as well. 295 </p> 296 <p> 297 If the optional <span class="bold"><strong>nosync</strong></span> argument is 298 specified, the log will not be synchronously flushed on transaction 299 commit. This means that transactions exhibit the ACI (atomicity, 300 consistency, and isolation) properties, but not D (durability); that 301 is, database integrity will be maintained, but it is possible that 302 some number of the most recently committed transactions may be undone 303 during recovery instead of being redone. 304 </p> 305 <p> 306 The number of transactions that are potentially at risk is governed by 307 how often the log is checkpointed (see 308 <a href="../C/db_checkpoint.html" class="olink">db_checkpoint</a> 309 in the <em class="citetitle">Berkeley DB C API</em> guide for more information) and how many 310 log updates can fit on a single log page. 311 </p> 312 </li> 313 <li> 314 <p> 315 <span class="bold"><strong>-txn_max max</strong></span> 316 </p> 317 <p> 318 Set the maximum number of simultaneous transactions that are supported 319 by the environment, which bounds the size of backing files. When 320 there are more than the specified number of concurrent transactions, 321 calls to <span class="emphasis"><em>env</em></span> <span class="bold"><strong>txn</strong></span> 322 will fail (until some active transactions complete). 323 </p> 324 </li> 325 <li> 326 <p> 327 <span class="bold"><strong>-use_environ</strong></span> 328 </p> 329 <p> 330 The Berkeley DB process' environment may be permitted to specify 331 information to be used when naming files; see 332 <a href="../../programmer_reference/env_naming.html" class="olink">Berkeley DB File Naming</a> 333 in the <em class="citetitle">Berkeley DB Programmer's Reference Guide</em>. Because 334 permitting users to specify which files are used can create security 335 problems, environment information will be used in file naming for all 336 users only if the <span class="bold"><strong>-use_environ</strong></span> flag 337 is set. 338 </p> 339 </li> 340 <li> 341 <p> 342 <span class="bold"><strong>-use_environ_root</strong></span> 343 </p> 344 <p> 345 The Berkeley DB process' environment may be permitted to specify 346 information to be used when naming files; see 347 <a href="../../programmer_reference/env_naming.html" class="olink">Berkeley DB File Naming</a> 348 in the <em class="citetitle">Berkeley DB Programmer's Reference Guide</em>. As 349 permitting users to specify which files are used can create security 350 problems, if the <span class="bold"><strong>-use_environ_root</strong></span> 351 flag is set, environment information will be used for file naming only 352 for users with appropriate permissions (for example, users with a 353 user-ID of 0 on IEEE/ANSI Std 1003.1 (POSIX) systems). 354 </p> 355 </li> 356 </ul> 357 </div> 358 <p> 359 The <span class="bold"><strong>berkdb env</strong></span> command returns an 360 environment handle on success. 361 </p> 362 <p> 363 In the case of error, a Tcl error is thrown. 364 </p> 365 </div> 366 <div class="navfooter"> 367 <hr /> 368 <table width="100%" summary="Navigation footer"> 369 <tr> 370 <td width="40%" align="left"><a accesskey="p" href="env_dbrename.html">Prev</a>��</td> 371 <td width="20%" align="center"> 372 <a accesskey="u" href="tclapi.html">Up</a> 373 </td> 374 <td width="40%" align="right">��<a accesskey="n" href="env_remove.html">Next</a></td> 375 </tr> 376 <tr> 377 <td width="40%" align="left" valign="top"><span class="emphasis"><em>env</em></span> dbrename��</td> 378 <td width="20%" align="center"> 379 <a accesskey="h" href="index.html">Home</a> 380 </td> 381 <td width="40%" align="right" valign="top">��berkdb envremove</td> 382 </tr> 383 </table> 384 </div> 385 </body> 386</html> 387