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>DB->get()</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 C API Reference" /> 10 <link rel="up" href="db.html" title="Chapter��2.�� The DB Handle" /> 11 <link rel="prev" href="dbfd.html" title="DB->fd()" /> 12 <link rel="next" href="dbget_bt_minkey.html" title="DB->get_bt_minkey()" /> 13 </head> 14 <body> 15 <div class="navheader"> 16 <table width="100%" summary="Navigation header"> 17 <tr> 18 <th colspan="3" align="center">DB->get()</th> 19 </tr> 20 <tr> 21 <td width="20%" align="left"><a accesskey="p" href="dbfd.html">Prev</a>��</td> 22 <th width="60%" align="center">Chapter��2.�� 23 The DB Handle 24 </th> 25 <td width="20%" align="right">��<a accesskey="n" href="dbget_bt_minkey.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="dbget"></a>DB->get()</h2> 35 </div> 36 </div> 37 </div> 38 <pre class="programlisting">#include <db.h> 39 40int 41DB->get(DB *db, 42 DB_TXN *txnid, DBT *key, DBT *data, u_int32_t flags); 43 44int 45DB->pget(DB *db, 46 DB_TXN *txnid, DBT *key, DBT *pkey, DBT *data, u_int32_t flags); </pre> 47 <p> 48 The <code class="methodname">DB->get()</code> method retrieves key/data pairs from the database. The 49 address and length of the data associated with the specified <span class="bold"><strong>key</strong></span> are returned in the structure to which 50 <span class="bold"><strong>data</strong></span> refers. 51 </p> 52 <p> 53 In the presence of duplicate key values, 54 <code class="methodname">DB->get()</code> will return the first data 55 item for the designated key. Duplicates are sorted by: 56 </p> 57 <div class="itemizedlist"> 58 <ul type="disc"> 59 <li> 60 <p> 61 Their sort order, if a duplicate sort function was specified. 62 </p> 63 </li> 64 <li> 65 <p> 66 Any explicit cursor designated insertion. 67 </p> 68 </li> 69 <li> 70 <p> 71 By insert order. This is the default behavior. 72 </p> 73 </li> 74 </ul> 75 </div> 76 <p> 77 <span class="bold"><strong>Retrieval of duplicates requires the 78 use of cursor operations.</strong></span> See 79 <a class="xref" href="dbcget.html" title="DBcursor->get()">DBcursor->get()</a> for details. 80 </p> 81 <p> 82 When called on a database that has been made into a secondary index 83 using the <a class="xref" href="dbassociate.html" title="DB->associate()">DB->associate()</a> 84 method, the <code class="methodname">DB->get()</code> and <code class="methodname">DB->pget()</code> 85 methods return the key from the secondary 86 index and the data item from the primary database. In addition, the 87 <code class="methodname">DB->pget()</code> method returns the key from the primary database. In 88 databases that are not secondary indices, the <code class="methodname">DB->pget()</code> method will 89 always fail. 90 </p> 91 <p> 92 The <code class="methodname">DB->get()</code> method will return <a href="../../programmer_reference/program_errorret.html#program_errorret.DB_NOTFOUND" class="olink">DB_NOTFOUND</a> if 93 the specified key is not in the database. The <code class="methodname">DB->get()</code> method will 94 return <a href="../../programmer_reference/program_errorret.html#program_errorret.DB_KEYEMPTY" class="olink">DB_KEYEMPTY</a> if 95 the database is a Queue or Recno database and the specified key 96 exists, but was never explicitly created by the application or was 97 later deleted. Unless otherwise specified, the 98 <code class="methodname">DB->get()</code> <span> 99 <span> 100 method returns a non-zero error value on failure and 0 on success. 101 </span> 102 103 </span> 104 </p> 105 <div class="sect2" lang="en" xml:lang="en"> 106 <div class="titlepage"> 107 <div> 108 <div> 109 <h3 class="title"><a id="id1634398"></a>Parameters</h3> 110 </div> 111 </div> 112 </div> 113 <div class="sect3" lang="en" xml:lang="en"> 114 <div class="titlepage"> 115 <div> 116 <div> 117 <h4 class="title"><a id="id1634708"></a>data</h4> 118 </div> 119 </div> 120 </div> 121 <p> 122 The data <a class="link" href="dbt.html" title="Chapter��4.�� The DBT Handle">DBT</a> operated on. 123 </p> 124 </div> 125 <div class="sect3" lang="en" xml:lang="en"> 126 <div class="titlepage"> 127 <div> 128 <div> 129 <h4 class="title"><a id="id1634754"></a>flags</h4> 130 </div> 131 </div> 132 </div> 133 <p> 134 The <span class="bold"><strong>flags</strong></span> parameter must be set to 0 135 or one of the following values: 136 </p> 137 <div class="itemizedlist"> 138 <ul type="disc"> 139 <li> 140 <p><a id="dbget_DB_CONSUME"></a> 141 <code class="literal">DB_CONSUME</code> 142 </p> 143 <p> 144 Return the record number and data from the available record closest to 145 the head of the queue, and delete the record. The record number will 146 be returned in <span class="bold"><strong>key</strong></span>, as described in 147 <a class="link" href="dbt.html" title="Chapter��4.�� The DBT Handle">DBT</a>. The data will be 148 returned in the <span class="bold"><strong>data</strong></span> parameter. A 149 record is available if it is not deleted and is not currently locked. 150 The underlying database must be of type Queue for DB_CONSUME to be 151 specified. 152 </p> 153 </li> 154 <li> 155 <p><a id="dbget_DB_CONSUME_WAIT"></a> 156 <code class="literal">DB_CONSUME_WAIT</code> 157 </p> 158 <p> 159 The DB_CONSUME_WAIT flag is the same as the DB_CONSUME flag, except 160 that if the Queue database is empty, the thread of control will wait 161 until there is data in the queue before returning. The underlying 162 database must be of type Queue for DB_CONSUME_WAIT to be specified. 163 </p> 164 <p> 165 If lock or transaction timeouts have been specified, the <code class="methodname">DB->get()</code> 166 method with the DB_CONSUME_WAIT flag may return <a href="../../programmer_reference/program_errorret.html#program_errorret.DB_LOCK_NOTGRANTED" class="olink">DB_LOCK_NOTGRANTED</a>. 167 This failure, by itself, does not require the enclosing transaction be 168 aborted. 169 </p> 170 </li> 171 <li> 172 <p><a id="get_DB_GET_BOTH"></a> 173 <code class="literal">DB_GET_BOTH</code> 174 </p> 175 <p> 176 Retrieve the key/data pair only if both the key and data match the 177 arguments. 178 </p> 179 <p> 180 When using a secondary index handle, the <code class="literal">DB_GET_BOTH</code>: 181 flag causes: 182 </p> 183 <div class="itemizedlist"> 184 <ul type="circle"> 185 <li> 186 <p> 187 the <code class="methodname">DB->pget()</code> version of 188 this method to retun the secondary key/primary 189 key/data tuple only if both the primary and 190 secondary keys match the arguments. 191 </p> 192 </li> 193 <li> 194 <p> 195 the <code class="methodname">DB->get()</code> version of this method 196 to result in an error. 197 </p> 198 </li> 199 </ul> 200 </div> 201 </li> 202 <li> 203 <p><a id="dbget_DB_SET_RECNO"></a> 204 <code class="literal">DB_SET_RECNO</code> 205 </p> 206 <p> 207 Retrieve the specified numbered key/data pair from a database. Upon 208 return, both the <span class="bold"><strong>key</strong></span> and <span class="bold"><strong>data</strong></span> items will have been filled in. 209 </p> 210 <p> 211 The <span class="bold"><strong>data</strong></span> field of the specified 212 <span class="bold"><strong>key</strong></span> must be a pointer to a logical 213 record number (that is, a <span class="bold"><strong>db_recno_t</strong></span>). This record number determines the 214 record to be retrieved. 215 </p> 216 <p> 217 For DB_SET_RECNO to be specified, the underlying database must be of 218 type Btree, and it must have been created with the DB_RECNUM flag. 219 </p> 220 </li> 221 </ul> 222 </div> 223 <p> 224 In addition, the following flags may be set by bitwise inclusively 225 <span class="bold"><strong>OR</strong></span>'ing them into the <span class="bold"><strong>flags</strong></span> parameter: 226 </p> 227 <div class="itemizedlist"> 228 <ul type="disc"> 229 <li> 230 <p><a id="get_DB_IGNORE_LEASE"></a> 231 <code class="literal">DB_IGNORE_LEASE</code> 232 </p> 233 <p> 234 Return the data item irrespective of the state of master leases. The 235 item will be returned under all conditions: if master leases are not 236 configured, if the request is made to a client, if the request is made 237 to a master with a valid lease, or if the request is made to a master 238 without a valid lease. 239 </p> 240 </li> 241 <li> 242 <p><a id="get_DB_MULTIPLE"></a> 243 <code class="literal">DB_MULTIPLE</code> 244 </p> 245 <p> 246 Return multiple data items in the buffer to which the <span class="bold"><strong>data</strong></span> parameter refers. 247 </p> 248 <p> 249 In the case of Btree or Hash databases, all of the data items 250 associated with the specified key are entered into the buffer. In the 251 case of Queue or Recno databases, all of the data items in the 252 database, starting at, and subsequent to, the specified key, are 253 entered into the buffer. 254 </p> 255 <p> 256 The buffer to which the <span class="bold"><strong>data</strong></span> 257 parameter refers must be provided from user memory (see 258 <a class="link" href="dbt.html#dbt_DB_DBT_USERMEM">DB_DBT_USERMEM</a>). 259 The buffer must be at least as large as the page size of the 260 underlying database, aligned for unsigned integer access, and be a 261 multiple of 1024 bytes in size. If the buffer size is insufficient, 262 then upon return from the call the size field of the <span class="bold"><strong>data</strong></span> parameter will have been set to an 263 estimated buffer size, and the error DB_BUFFER_SMALL is returned. 264 (The size is an estimate as the exact size needed may not be known 265 until all entries are read. It is best to initially provide a 266 relatively large buffer, but applications should be prepared to resize 267 the buffer as necessary and repeatedly call the method.) 268 </p> 269 <p> 270 The DB_MULTIPLE flag may only be used alone, or with the DB_GET_BOTH 271 and DB_SET_RECNO options. The DB_MULTIPLE flag may not be used when 272 accessing databases made into secondary indices using the 273 <a class="xref" href="dbassociate.html" title="DB->associate()">DB->associate()</a> method. 274 </p> 275 <p> 276 See the <a class="xref" href="dbt.html#dbtlist" title="DBT and Bulk Operations">DBT and Bulk Operations</a> 277 for more information on working with bulk get. 278 </p> 279 </li> 280 <li> 281 <p><a id="get_DB_READ_COMMITTED"></a> 282 <code class="literal">DB_READ_COMMITTED</code> 283 </p> 284 <p> 285 Configure a transactional get operation to have degree 2 isolation 286 (the read is not repeatable). 287 </p> 288 </li> 289 <li> 290 <p><a id="get_DB_READ_UNCOMMITTED"></a> 291 <code class="literal">DB_READ_UNCOMMITTED</code> 292 </p> 293 <p> 294 Configure a transactional get operation to have degree 1 isolation, 295 reading modified but not yet committed data. Silently ignored if the 296 <a class="link" href="dbopen.html#dbopen_DB_READ_UNCOMMITTED">DB_READ_UNCOMMITTED</a> 297 flag was not specified when the underlying database was opened. 298 </p> 299 </li> 300 <li> 301 <p><a id="get_DB_RMW"></a> 302 <code class="literal">DB_RMW</code> 303 </p> 304 <p> 305 Acquire write locks instead of read locks when doing the read, if 306 locking is configured. Setting this flag can eliminate deadlock 307 during a read-modify-write cycle by acquiring the write lock during 308 the read part of the cycle so that another thread of control acquiring 309 a read lock for the same item, in its own read-modify-write cycle, 310 will not result in deadlock. 311 </p> 312 <p> 313 Because the <code class="methodname">DB->get()</code> method will not hold locks across Berkeley DB 314 calls in non-transactional operations, the 315 <a class="link" href="dbcget.html#dbcget_DB_RMW">DB_RMW</a> flag to the 316 <code class="methodname">DB->get()</code> call is meaningful only in the presence of transactions. 317 </p> 318 </li> 319 </ul> 320 </div> 321 </div> 322 <div class="sect3" lang="en" xml:lang="en"> 323 <div class="titlepage"> 324 <div> 325 <div> 326 <h4 class="title"><a id="id1635213"></a>key</h4> 327 </div> 328 </div> 329 </div> 330 <p> 331 The key <a class="link" href="dbt.html" title="Chapter��4.�� The DBT Handle">DBT</a> operated on. 332 </p> 333 </div> 334 <div class="sect3" lang="en" xml:lang="en"> 335 <div class="titlepage"> 336 <div> 337 <div> 338 <h4 class="title"><a id="id1634709"></a>pkey</h4> 339 </div> 340 </div> 341 </div> 342 <p> 343 The <span class="bold"><strong>pkey</strong></span> parameter is the return key 344 from the primary database. 345 </p> 346 </div> 347 <div class="sect3" lang="en" xml:lang="en"> 348 <div class="titlepage"> 349 <div> 350 <div> 351 <h4 class="title"><a id="id1635117"></a>txnid</h4> 352 </div> 353 </div> 354 </div> 355 <p> 356 If the operation is part of an application-specified transaction, the 357 <span class="bold"><strong>txnid</strong></span> parameter is a transaction 358 handle returned from <a class="xref" href="txnbegin.html" title="DB_ENV->txn_begin()">DB_ENV->txn_begin()</a>; 359 if the operation is part of a Berkeley DB Concurrent Data Store group, the 360 <span class="bold"><strong>txnid</strong></span> parameter is a handle returned 361 from <a class="xref" href="envcdsgroup_begin.html" title="DB_ENV->cdsgroup_begin()">DB_ENV->cdsgroup_begin()</a>; 362 otherwise NULL. If no transaction handle is specified, but the 363 operation occurs in a transactional database, the operation will be 364 implicitly transaction protected. 365 </p> 366 </div> 367 </div> 368 <div class="sect2" lang="en" xml:lang="en"> 369 <div class="titlepage"> 370 <div> 371 <div> 372 <h3 class="title"><a id="id1634360"></a>Errors</h3> 373 </div> 374 </div> 375 </div> 376 <p> 377 The <code class="methodname">DB->get()</code> <span> 378 <span> 379 method may fail and return one of the following non-zero errors: 380 </span> 381 382 </span> 383 </p> 384 <div class="sect3" lang="en" xml:lang="en"> 385 <div class="titlepage"> 386 <div> 387 <div> 388 <h4 class="title"><a id="id1635426"></a>DB_BUFFER_SMALL</h4> 389 </div> 390 </div> 391 </div> 392 <p> 393 The requested item could not be returned due to undersized buffer. 394 </p> 395 </div> 396 <div class="sect3" lang="en" xml:lang="en"> 397 <div class="titlepage"> 398 <div> 399 <div> 400 <h4 class="title"><a id="id1635125"></a>DB_LOCK_DEADLOCK</h4> 401 </div> 402 </div> 403 </div> 404 <p> 405 A transactional database environment operation was selected to resolve 406 a deadlock. 407 </p> 408 </div> 409 <div class="sect3" lang="en" xml:lang="en"> 410 <div class="titlepage"> 411 <div> 412 <div> 413 <h4 class="title"><a id="id1635087"></a>DB_LOCK_NOTGRANTED</h4> 414 </div> 415 </div> 416 </div> 417 <p> 418 A Berkeley DB Concurrent Data Store database environment configured 419 for lock timeouts was unable to grant a lock in the allowed time. 420 </p> 421 </div> 422 <div class="sect3" lang="en" xml:lang="en"> 423 <div class="titlepage"> 424 <div> 425 <div> 426 <h4 class="title"><a id="id1635112"></a>DB_LOCK_NOTGRANTED</h4> 427 </div> 428 </div> 429 </div> 430 <p> 431 The <code class="literal">DB_CONSUME_WAIT</code> flag was specified, lock or transaction timers 432 were configured and the lock could not be granted before the wait-time 433 expired. 434 </p> 435 </div> 436 <div class="sect3" lang="en" xml:lang="en"> 437 <div class="titlepage"> 438 <div> 439 <div> 440 <h4 class="title"><a id="id1634745"></a> DB_REP_HANDLE_DEAD</h4> 441 </div> 442 </div> 443 </div> 444 <p> 445 When a client synchronizes with the master, it is possible for committed 446 transactions to be rolled back. This invalidates all the database and cursor 447 handles opened in the replication environment. Once this occurs, an attempt to use 448 such a handle will 449 450 return <code class="literal">DB_REP_HANDLE_DEAD</code>. 451 The application will need to discard the handle and open a new one in order to 452 continue processing. 453 </p> 454 </div> 455 <div class="sect3" lang="en" xml:lang="en"> 456 <div class="titlepage"> 457 <div> 458 <div> 459 <h4 class="title"><a id="id1635405"></a>DB_REP_LEASE_EXPIRED</h4> 460 </div> 461 </div> 462 </div> 463 <p> 464 The operation failed because the site's replication master lease has expired. 465 </p> 466 </div> 467 <div class="sect3" lang="en" xml:lang="en"> 468 <div class="titlepage"> 469 <div> 470 <div> 471 <h4 class="title"><a id="id1635202"></a>DB_REP_LOCKOUT</h4> 472 </div> 473 </div> 474 </div> 475 <p> 476 The operation was blocked by client/master synchronization. 477 </p> 478 </div> 479 <div class="sect3" lang="en" xml:lang="en"> 480 <div class="titlepage"> 481 <div> 482 <div> 483 <h4 class="title"><a id="id1634888"></a>DB_SECONDARY_BAD</h4> 484 </div> 485 </div> 486 </div> 487 <p> 488 A secondary index references a nonexistent primary key. 489 </p> 490 </div> 491 <div class="sect3" lang="en" xml:lang="en"> 492 <div class="titlepage"> 493 <div> 494 <div> 495 <h4 class="title"><a id="id1635167"></a>EINVAL</h4> 496 </div> 497 </div> 498 </div> 499 <p> 500 If a record number of 0 was specified; the 501 <a class="link" href="envopen.html#envopen_DB_THREAD">DB_THREAD</a> flag was 502 specified to the <a class="xref" href="dbopen.html" title="DB->open()">DB->open()</a> method and none of the 503 <a class="link" href="dbt.html#dbt_DB_DBT_MALLOC">DB_DBT_MALLOC</a>, 504 <a class="link" href="dbt.html#dbt_DB_DBT_REALLOC">DB_DBT_REALLOC</a> or 505 <a class="link" href="dbt.html#dbt_DB_DBT_USERMEM">DB_DBT_USERMEM</a> 506 flags were set in the <a class="link" href="dbt.html" title="Chapter��4.�� The DBT Handle">DBT</a>; 507 the <code class="methodname">DB->pget()</code> method was called with a 508 <a class="link" href="db.html" title="Chapter��2.�� The DB Handle">DB</a> handle 509 that does not refer to a secondary index; or if an invalid flag value 510 or parameter was specified. 511 </p> 512 </div> 513 </div> 514 <div class="sect2" lang="en" xml:lang="en"> 515 <div class="titlepage"> 516 <div> 517 <div> 518 <h3 class="title"><a id="id1635252"></a>Class</h3> 519 </div> 520 </div> 521 </div> 522 <p> 523 <a class="link" href="db.html" title="Chapter��2.�� The DB Handle">DB</a> 524 </p> 525 </div> 526 <div class="sect2" lang="en" xml:lang="en"> 527 <div class="titlepage"> 528 <div> 529 <div> 530 <h3 class="title"><a id="id1634720"></a>See Also</h3> 531 </div> 532 </div> 533 </div> 534 <p> 535 <a class="xref" href="db.html#dblist" title="Database and Related Methods">Database and Related Methods</a> 536 </p> 537 </div> 538 </div> 539 <div class="navfooter"> 540 <hr /> 541 <table width="100%" summary="Navigation footer"> 542 <tr> 543 <td width="40%" align="left"><a accesskey="p" href="dbfd.html">Prev</a>��</td> 544 <td width="20%" align="center"> 545 <a accesskey="u" href="db.html">Up</a> 546 </td> 547 <td width="40%" align="right">��<a accesskey="n" href="dbget_bt_minkey.html">Next</a></td> 548 </tr> 549 <tr> 550 <td width="40%" align="left" valign="top">DB->fd()��</td> 551 <td width="20%" align="center"> 552 <a accesskey="h" href="index.html">Home</a> 553 </td> 554 <td width="40%" align="right" valign="top">��DB->get_bt_minkey()</td> 555 </tr> 556 </table> 557 </div> 558 </body> 559</html> 560