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32 .\" @(#)dbopen.3 8.5 (Berkeley) 1/2/94
34 .TH DBOPEN 3 1994-01-02 "" "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 is the library interface to database files.
51 The supported file formats are btree, hashed and UNIX file oriented.
52 The btree format is a representation of a sorted, balanced tree structure.
53 The hashed format is an extensible, dynamic hashing scheme.
54 The flat-file format is a byte stream file with fixed or variable length
56 The formats and file format specific information are described in detail
57 in their respective manual pages
66 for reading and/or writing.
67 Files never intended to be preserved on disk may be created by setting
76 arguments are as specified to the
78 routine, however, only the
89 (Note, opening a database file
92 .\"Three additional options may be specified by ORing
98 .\"Do the necessary locking in the database to support concurrent access.
99 .\"If concurrent access isn't needed or the database is read-only this
100 .\"flag should not be set, as it tends to have an associated performance
104 .\"Place the underlying memory pool used by the database in shared
106 .\"Necessary for concurrent access.
109 .\"Support transactions in the database.
110 .\"The DB_LOCK and DB_SHMEM flags must be set as well.
127 argument is a pointer to an access method specific structure described
128 in the access method's manual page.
131 is NULL, each access method will use defaults appropriate for the system
132 and the access method.
135 returns a pointer to a
137 structure on success and NULL on error.
140 structure is defined in the
142 include file, and contains at
143 least the following fields:
149 int (*close)(const DB *db);
150 int (*del)(const DB *db, const DBT *key, unsigned int flags);
151 int (*fd)(const DB *db);
152 int (*get)(const DB *db, DBT *key, DBT *data,
154 int (*put)(const DB *db, DBT *key, const DBT *data,
156 int (*sync)(const DB *db, unsigned int flags);
157 int (*seq)(const DB *db, DBT *key, DBT *data,
163 These elements describe a database type and a set of functions performing
165 These functions take a pointer to a structure as returned by
167 and sometimes one or more pointers to key/data structures and a flag value.
170 The type of the underlying access method (and file format).
173 A pointer to a routine to flush any cached information to disk, free any
174 allocated resources, and close the underlying file(s).
175 Since key/data pairs may be cached in memory, failing to sync the file
180 function may result in inconsistent or lost information.
182 routines return \-1 on error (setting
187 A pointer to a routine to remove key/data pairs from the database.
191 may be set to the following value:
195 Delete the record referenced by the cursor.
196 The cursor must have previously been initialized.
200 routines return \-1 on error (setting
202 0 on success, and 1 if the specified
207 A pointer to a routine which returns a file descriptor representative
208 of the underlying database.
209 A file descriptor referencing the same file will be returned to all
215 This file descriptor may be safely used as an argument to the
220 The file descriptor is not necessarily associated with any of the
221 underlying files used by the access method.
222 No file descriptor is available for in memory databases.
224 routines return \-1 on error (setting
226 and the file descriptor on success.
229 A pointer to a routine which is the interface for keyed retrieval from
231 The address and length of the data associated with the specified
233 are returned in the structure referenced by
236 routines return \-1 on error (setting
238 0 on success, and 1 if the
243 A pointer to a routine to store key/data pairs in the database.
247 may be set to one of the following values:
251 Replace the key/data pair referenced by the cursor.
252 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
266 Insert the data immediately before the data referenced by
268 creating a new key/data pair.
269 The record number of the inserted key/data pair is returned in the
272 (Applicable only to the
277 Enter the new key/data pair only if the key does not previously exist.
280 Store the key/data pair, setting or initializing the position of the
281 cursor to reference it.
282 (Applicable only to the
290 is available only for the
295 methods because it implies that the keys have an inherent order
296 which does not change.
301 are available only for the
303 access method because they each imply that the access method is able to
305 This is only true if the keys are ordered and independent, record numbers
308 The default behavior of the
310 routines is to enter the new key/data pair, replacing any previously
314 routines return \-1 on error (setting
316 0 on success, and 1 if the
319 was set and the key already exists in the file.
322 A pointer to a routine which is the interface for sequential
323 retrieval from the database.
324 The address and length of the key are returned in the structure
327 and the address and length of the data are returned in the
332 Sequential key/data pair retrieval may begin at any time, and the
333 position of the "cursor" is not affected by calls to the
340 Modifications to the database during a sequential scan will be reflected
341 in the scan, that is,
342 records inserted behind the cursor will not be returned
343 while records inserted in front of the cursor will be returned.
347 be set to one of the following values:
351 The data associated with the specified key is returned.
352 This differs from the
354 routines in that it sets or initializes the cursor to the location of
358 access method, the returned key is not necessarily an
359 exact match for the specified key.
360 The returned key is the smallest key greater than or equal to the specified
361 key, permitting partial key matches and range searches.)
364 The first key/data pair of the database is returned, and the cursor
365 is set or initialized to reference it.
368 The last key/data pair of the database is returned, and the cursor
369 is set or initialized to reference it.
370 (Applicable only to the
377 Retrieve the key/data pair immediately after the cursor.
378 If the cursor is not yet set, this is the same as the
383 Retrieve the key/data pair immediately before the cursor.
384 If the cursor is not yet set, this is the same as the
387 (Applicable only to the
397 are available only for the
401 access methods because they each imply that the keys have an inherent
402 order which does not change.
405 routines return \-1 on error (setting
407 0 on success and 1 if there are no key/data pairs less than or greater
408 than the specified or current key.
411 access method is being used, and if the database file
412 is a character special file and no complete key/data pairs are currently
418 A pointer to a routine to flush any cached information to disk.
419 If the database is in memory only, the
421 routine has no effect and will always succeed.
423 The flag value may be set to the following value:
429 access method is being used, this flag causes
430 the sync routine to apply to the btree file which underlies the
431 recno file, not the recno file itself.
436 manual page for more information.)
440 routines return \-1 on error (setting
444 Access to all file types is based on key/data pairs.
445 Both keys and data are represented by the following data structure:
458 structure are defined as follows:
461 A pointer to a byte string.
464 The length of the byte string.
466 Key and data byte strings may reference strings of essentially unlimited
467 length although any two of them must fit into available memory at the same
469 It should be noted that the access methods provide no guarantees about
470 byte string alignment.
474 routine may fail and set
476 for any of the errors specified for the library routines
483 A file is incorrectly formatted.
486 A parameter has been specified (hash function, pad byte etc.) that is
487 incompatible with the current file specification or which is not
488 meaningful for the function (for example, use of the cursor without
489 prior initialization) or there is a mismatch between the version
490 number of file and the software.
494 routines may fail and set
496 for any of the errors specified for the library routines
510 routines may fail and set
512 for any of the errors specified for the library routines
521 routines will fail and set
525 for in memory databases.
529 routines may fail and set
531 for any of the errors specified for the library routine
536 is a mnemonic for "data base thang", and was used
537 because no-one could think of a reasonable name that wasn't already used.
539 The file descriptor interface is a kludge and will be deleted in a
540 future version of the interface.
542 None of the access methods provide any form of concurrent access,
543 locking, or transactions.
550 .IR "LIBTP: Portable, Modular Transactions for UNIX" ,
551 Margo Seltzer, Michael Olson, USENIX proceedings, Winter 1992.