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32 .\" @(#)dbopen.3 8.5 (Berkeley) 1/2/94
34 .TH DBOPEN 3 2012-04-23 "" "Linux Programmer's Manual"
37 dbopen \- database access methods
40 .B #include <sys/types.h>
41 .B #include <limits.h>
44 .BI "DB *dbopen(const char *" file ", int " flags ", int " mode \
46 .BI " const void *" openinfo );
50 This page documents interfaces provided in glibc up until version 2.1.
51 Since version 2.2, glibc no longer provides these interfaces.
52 Probably, you are looking for the APIs provided by the
57 is the library interface to database files.
58 The supported file formats are btree, hashed and UNIX file oriented.
59 The btree format is a representation of a sorted, balanced tree structure.
60 The hashed format is an extensible, dynamic hashing scheme.
61 The flat-file format is a byte stream file with fixed or variable length
63 The formats and file format specific information are described in detail
64 in their respective manual pages
73 for reading and/or writing.
74 Files never intended to be preserved on disk may be created by setting
83 arguments are as specified to the
85 routine, however, only the
96 (Note, opening a database file
99 .\"Three additional options may be specified by ORing
105 .\"Do the necessary locking in the database to support concurrent access.
106 .\"If concurrent access isn't needed or the database is read-only this
107 .\"flag should not be set, as it tends to have an associated performance
111 .\"Place the underlying memory pool used by the database in shared
113 .\"Necessary for concurrent access.
116 .\"Support transactions in the database.
117 .\"The DB_LOCK and DB_SHMEM flags must be set as well.
134 argument is a pointer to an access method specific structure described
135 in the access method's manual page.
138 is NULL, each access method will use defaults appropriate for the system
139 and the access method.
142 returns a pointer to a
144 structure on success and NULL on error.
147 structure is defined in the
149 include file, and contains at
150 least the following fields:
156 int (*close)(const DB *db);
157 int (*del)(const DB *db, const DBT *key, unsigned int flags);
158 int (*fd)(const DB *db);
159 int (*get)(const DB *db, DBT *key, DBT *data,
161 int (*put)(const DB *db, DBT *key, const DBT *data,
163 int (*sync)(const DB *db, unsigned int flags);
164 int (*seq)(const DB *db, DBT *key, DBT *data,
170 These elements describe a database type and a set of functions performing
172 These functions take a pointer to a structure as returned by
174 and sometimes one or more pointers to key/data structures and a flag value.
177 The type of the underlying access method (and file format).
180 A pointer to a routine to flush any cached information to disk, free any
181 allocated resources, and close the underlying file(s).
182 Since key/data pairs may be cached in memory, failing to sync the file
187 function may result in inconsistent or lost information.
189 routines return \-1 on error (setting
194 A pointer to a routine to remove key/data pairs from the database.
198 may be set to the following value:
202 Delete the record referenced by the cursor.
203 The cursor must have previously been initialized.
207 routines return \-1 on error (setting
209 0 on success, and 1 if the specified
214 A pointer to a routine which returns a file descriptor representative
215 of the underlying database.
216 A file descriptor referencing the same file will be returned to all
222 This file descriptor may be safely used as an argument to the
227 The file descriptor is not necessarily associated with any of the
228 underlying files used by the access method.
229 No file descriptor is available for in memory databases.
231 routines return \-1 on error (setting
233 and the file descriptor on success.
236 A pointer to a routine which is the interface for keyed retrieval from
238 The address and length of the data associated with the specified
240 are returned in the structure referenced by
243 routines return \-1 on error (setting
245 0 on success, and 1 if the
250 A pointer to a routine to store key/data pairs in the database.
254 may be set to one of the following values:
258 Replace the key/data pair referenced by the cursor.
259 The cursor must have previously been initialized.
262 Append the data immediately after the data referenced by
264 creating a new key/data pair.
265 The record number of the appended key/data pair is returned in the
268 (Applicable only to the
273 Insert the data immediately before the data referenced by
275 creating a new key/data pair.
276 The record number of the inserted key/data pair is returned in the
279 (Applicable only to the
284 Enter the new key/data pair only if the key does not previously exist.
287 Store the key/data pair, setting or initializing the position of the
288 cursor to reference it.
289 (Applicable only to the
297 is available only for the
302 methods because it implies that the keys have an inherent order
303 which does not change.
308 are available only for the
310 access method because they each imply that the access method is able to
312 This is only true if the keys are ordered and independent, record numbers
315 The default behavior of the
317 routines is to enter the new key/data pair, replacing any previously
321 routines return \-1 on error (setting
323 0 on success, and 1 if the
326 was set and the key already exists in the file.
329 A pointer to a routine which is the interface for sequential
330 retrieval from the database.
331 The address and length of the key are returned in the structure
334 and the address and length of the data are returned in the
339 Sequential key/data pair retrieval may begin at any time, and the
340 position of the "cursor" is not affected by calls to the
347 Modifications to the database during a sequential scan will be reflected
348 in the scan, that is,
349 records inserted behind the cursor will not be returned
350 while records inserted in front of the cursor will be returned.
354 be set to one of the following values:
358 The data associated with the specified key is returned.
359 This differs from the
361 routines in that it sets or initializes the cursor to the location of
365 access method, the returned key is not necessarily an
366 exact match for the specified key.
367 The returned key is the smallest key greater than or equal to the specified
368 key, permitting partial key matches and range searches.)
371 The first key/data pair of the database is returned, and the cursor
372 is set or initialized to reference it.
375 The last key/data pair of the database is returned, and the cursor
376 is set or initialized to reference it.
377 (Applicable only to the
384 Retrieve the key/data pair immediately after the cursor.
385 If the cursor is not yet set, this is the same as the
390 Retrieve the key/data pair immediately before the cursor.
391 If the cursor is not yet set, this is the same as the
394 (Applicable only to the
404 are available only for the
408 access methods because they each imply that the keys have an inherent
409 order which does not change.
412 routines return \-1 on error (setting
414 0 on success and 1 if there are no key/data pairs less than or greater
415 than the specified or current key.
418 access method is being used, and if the database file
419 is a character special file and no complete key/data pairs are currently
425 A pointer to a routine to flush any cached information to disk.
426 If the database is in memory only, the
428 routine has no effect and will always succeed.
430 The flag value may be set to the following value:
436 access method is being used, this flag causes
437 the sync routine to apply to the btree file which underlies the
438 recno file, not the recno file itself.
443 manual page for more information.)
447 routines return \-1 on error (setting
451 Access to all file types is based on key/data pairs.
452 Both keys and data are represented by the following data structure:
465 structure are defined as follows:
468 A pointer to a byte string.
471 The length of the byte string.
473 Key and data byte strings may reference strings of essentially unlimited
474 length although any two of them must fit into available memory at the same
476 It should be noted that the access methods provide no guarantees about
477 byte string alignment.
481 routine may fail and set
483 for any of the errors specified for the library routines
490 A file is incorrectly formatted.
493 A parameter has been specified (hash function, pad byte etc.) that is
494 incompatible with the current file specification or which is not
495 meaningful for the function (for example, use of the cursor without
496 prior initialization) or there is a mismatch between the version
497 number of file and the software.
501 routines may fail and set
503 for any of the errors specified for the library routines
517 routines may fail and set
519 for any of the errors specified for the library routines
528 routines will fail and set
532 for in memory databases.
536 routines may fail and set
538 for any of the errors specified for the library routine
543 is a mnemonic for "data base thang", and was used
544 because no-one could think of a reasonable name that wasn't already used.
546 The file descriptor interface is a kludge and will be deleted in a
547 future version of the interface.
549 None of the access methods provide any form of concurrent access,
550 locking, or transactions.
557 .IR "LIBTP: Portable, Modular Transactions for UNIX" ,
558 Margo Seltzer, Michael Olson, USENIX proceedings, Winter 1992.