1 .\" Copyright (c) 1990, 1993
2 .\" The Regents of the University of California. All rights reserved.
4 .\" Redistribution and use in source and binary forms, with or without
5 .\" modification, are permitted provided that the following conditions
7 .\" 1. Redistributions of source code must retain the above copyright
8 .\" notice, this list of conditions and the following disclaimer.
9 .\" 2. Redistributions in binary form must reproduce the above copyright
10 .\" notice, this list of conditions and the following disclaimer in the
11 .\" documentation and/or other materials provided with the distribution.
12 .\" 3. Neither the name of the University nor the names of its contributors
13 .\" may be used to endorse or promote products derived from this software
14 .\" without specific prior written permission.
16 .\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
17 .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
18 .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
19 .\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
20 .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
21 .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
22 .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
23 .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
24 .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
25 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
28 .\" @(#)dbopen.3 8.5 (Berkeley) 1/2/94
29 .\" $FreeBSD: src/lib/libc/db/man/dbopen.3,v 1.3.2.3 2003/02/23 19:45:52 trhodes Exp $
30 .\" $DragonFly: src/lib/libc/db/man/dbopen.3,v 1.6 2007/08/18 20:48:47 swildner Exp $
32 .Dd September 19, 2005
37 .Nd "database access methods"
46 .Fn dbopen "const char *file" "int flags" "mode_t mode" "DBTYPE type" "const void *openinfo"
51 is the library interface to database files.
52 The supported file formats are btree, hashed and
55 The btree format is a representation of a sorted, balanced tree structure.
56 The hashed format is an extensible, dynamic hashing scheme.
57 The flat-file format is a byte stream file with fixed or variable length
59 The formats and file format specific information are described in detail
60 in their respective manual pages
71 for reading and/or writing.
72 Files never intended to be preserved on disk may be created by setting
83 are as specified to the
85 routine, however, only the
86 .Dv O_CREAT , O_EXCL , O_EXLOCK , O_NONBLOCK ,
87 .Dv O_RDONLY , O_RDWR , O_SHLOCK
91 (Note, opening a database file
94 .\"Three additional options may be specified by
99 .\".Bl -tag -width indent
101 .\"Do the necessary locking in the database to support concurrent access.
102 .\"If concurrent access isn't needed or the database is read-only this
103 .\"flag should not be set, as it tends to have an associated performance
106 .\"Place the underlying memory pool used by the database in shared
108 .\"Necessary for concurrent access.
110 .\"Support transactions in the database.
115 .\"flags must be set as well.
126 .Dv DB_BTREE , DB_HASH
132 argument is a pointer to an access method specific structure described
133 in the access method's manual page.
138 each access method will use defaults appropriate for the system
139 and the access method.
144 returns a pointer to a
146 structure on success and
151 structure is defined in the
153 include file, and contains at
154 least the following fields:
158 int (*close)(const DB *db);
159 int (*del)(const DB *db, const DBT *key, u_int flags);
160 int (*fd)(const DB *db);
161 int (*get)(const DB *db, DBT *key, DBT *data, u_int flags);
162 int (*put)(const DB *db, DBT *key, const DBT *data,
164 int (*sync)(const DB *db, u_int flags);
165 int (*seq)(const DB *db, DBT *key, DBT *data, u_int flags);
169 These elements describe a database type and a set of functions performing
171 These functions take a pointer to a structure as returned by
173 and sometimes one or more pointers to key/data structures and a flag value.
174 .Bl -tag -width indent
176 The type of the underlying access method (and file format).
178 A pointer to a routine to flush any cached information to disk, free any
179 allocated resources, and close the underlying file(s).
180 Since key/data pairs may be cached in memory, failing to sync the file
185 function may result in inconsistent or lost information.
187 routines return -1 on error (setting
191 A pointer to a routine to remove key/data pairs from the database.
196 may be set to the following value:
197 .Bl -tag -width indent
199 Delete the record referenced by the cursor.
200 The cursor must have previously been initialized.
204 routines return -1 on error (setting
206 0 on success, and 1 if the specified
210 A pointer to a routine which returns a file descriptor representative
211 of the underlying database.
212 A file descriptor referencing the same file will be returned to all
218 This file descriptor may be safely used as an argument to the
223 The file descriptor is not necessarily associated with any of the
224 underlying files used by the access method.
225 No file descriptor is available for in memory databases.
227 routines return -1 on error (setting
229 and the file descriptor on success.
231 A pointer to a routine which is the interface for keyed retrieval from
233 The address and length of the data associated with the specified
235 are returned in the structure referenced by
238 routines return -1 on error (setting
240 0 on success, and 1 if the
244 A pointer to a routine to store key/data pairs in the database.
249 may be set to one of the following values:
250 .Bl -tag -width indent
252 Replace the key/data pair referenced by the cursor.
253 The cursor must have previously been initialized.
255 Append the data immediately after the data referenced by
257 creating a new key/data pair.
258 The record number of the appended key/data pair is returned in the
261 (Applicable only to the
265 Insert the data immediately before the data referenced by
267 creating a new key/data pair.
268 The record number of the inserted key/data pair is returned in the
271 (Applicable only to the
275 Enter the new key/data pair only if the key does not previously exist.
277 Store the key/data pair, setting or initializing the position of the
278 cursor to reference it.
279 (Applicable only to the
287 is available only for the
292 methods because it implies that the keys have an inherent order
293 which does not change.
298 are available only for the
300 access method because they each imply that the access method is able to
302 This is only true if the keys are ordered and independent, record numbers
305 The default behavior of the
307 routines is to enter the new key/data pair, replacing any previously
311 routines return -1 on error (setting
313 0 on success, and 1 if the
316 was set and the key already exists in the file.
318 A pointer to a routine which is the interface for sequential
319 retrieval from the database.
320 The address and length of the key are returned in the structure
323 and the address and length of the data are returned in the
328 Sequential key/data pair retrieval may begin at any time, and the
331 is not affected by calls to the
338 Modifications to the database during a sequential scan will be reflected
339 in the scan, i.e. records inserted behind the cursor will not be returned
340 while records inserted in front of the cursor will be returned.
346 be set to one of the following values:
347 .Bl -tag -width indent
349 The data associated with the specified key is returned.
350 This differs from the
352 routines in that it sets or initializes the cursor to the location of
356 access method, the returned key is not necessarily an
357 exact match for the specified key.
358 The returned key is the smallest key greater than or equal to the specified
359 key, permitting partial key matches and range searches.)
361 The first key/data pair of the database is returned, and the cursor
362 is set or initialized to reference it.
364 The last key/data pair of the database is returned, and the cursor
365 is set or initialized to reference it.
366 (Applicable only to the
372 Retrieve the key/data pair immediately after the cursor.
373 If the cursor is not yet set, this is the same as the
377 Retrieve the key/data pair immediately before the cursor.
378 If the cursor is not yet set, this is the same as the
381 (Applicable only to the
391 are available only for the
395 access methods because they each imply that the keys have an inherent
396 order which does not change.
399 routines return -1 on error (setting
401 0 on success and 1 if there are no key/data pairs less than or greater
402 than the specified or current key.
405 access method is being used, and if the database file
406 is a character special file and no complete key/data pairs are currently
411 A pointer to a routine to flush any cached information to disk.
412 If the database is in memory only, the
414 routine has no effect and will always succeed.
418 argument may be set to the following value:
419 .Bl -tag -width indent
423 access method is being used, this flag causes
426 routine to apply to the btree file which underlies the
427 recno file, not the recno file itself.
432 manual page for more information.)
436 routines return -1 on error (setting
441 Access to all file types is based on key/data pairs.
442 Both keys and data are represented by the following data structure:
452 structure are defined as follows:
453 .Bl -tag -width "data"
455 A pointer to a byte string.
457 The length of the byte string.
460 Key and data byte strings may reference strings of essentially unlimited
461 length although any two of them must fit into available memory at the same
463 It should be noted that the access methods provide no guarantees about
464 byte string alignment.
468 routine may fail and set
470 for any of the errors specified for the library routines
477 A file is incorrectly formatted.
479 An argument has been specified (hash function, pad byte etc.) that is
480 incompatible with the current file specification or which is not
481 meaningful for the function (for example, use of the cursor without
482 prior initialization) or there is a mismatch between the version
483 number of file and the software.
488 routines may fail and set
490 for any of the errors specified for the library routines
504 routines may fail and set
506 for any of the errors specified for the library routines
515 routines will fail and set
519 for in memory databases.
523 routines may fail and set
525 for any of the errors specified for the library routine
533 .%T "LIBTP: Portable, Modular Transactions for UNIX"
536 .%R "USENIX proceedings"
543 .Dq "data base thang" ,
545 because noone could think of a reasonable name that wasn't already used.
547 The file descriptor interface is a kluge and will be deleted in a
548 future version of the interface.
550 None of the access methods provide any form of concurrent access,
551 locking, or transactions.