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32 .\" @(#)dbopen.3 8.5 (Berkeley) 1/2/94
35 .TH DBOPEN 3 "January 2, 1994"
38 dbopen \- database access methods
42 #include <sys/types.h>
47 dbopen(const char *file, int flags, int mode, DBTYPE type,
49 const void *openinfo);
54 is the library interface to database files.
55 The supported file formats are btree, hashed and UNIX file oriented.
56 The btree format is a representation of a sorted, balanced tree structure.
57 The hashed format is an extensible, dynamic hashing scheme.
58 The flat-file format is a byte stream file with fixed or variable length
60 The formats and file format specific information are described in detail
61 in their respective manual pages
69 for reading and/or writing.
70 Files never intended to be preserved on disk may be created by setting
71 the file parameter to NULL.
77 are as specified to the
79 routine, however, only the O_CREAT, O_EXCL, O_EXLOCK, O_NONBLOCK,
80 O_RDONLY, O_RDWR, O_SHLOCK and O_TRUNC flags are meaningful.
81 (Note, opening a database file O_WRONLY is not possible.)
82 .\"Three additional options may be specified by
89 .\"Do the necessary locking in the database to support concurrent access.
90 .\"If concurrent access isn't needed or the database is read-only this
91 .\"flag should not be set, as it tends to have an associated performance
95 .\"Place the underlying memory pool used by the database in shared
97 .\"Necessary for concurrent access.
100 .\"Support transactions in the database.
101 .\"The DB_LOCK and DB_SHMEM flags must be set as well.
105 argument is of type DBTYPE (as defined in the <db.h> include file) and
106 may be set to DB_BTREE, DB_HASH or DB_RECNO.
110 argument is a pointer to an access method specific structure described
111 in the access method's manual page.
114 is NULL, each access method will use defaults appropriate for the system
115 and the access method.
118 returns a pointer to a DB structure on success and NULL on error.
119 The DB structure is defined in the <db.h> include file, and contains at
120 least the following fields:
126 int (*close)(const DB *db);
127 int (*del)(const DB *db, const DBT *key, u_int flags);
128 int (*fd)(const DB *db);
129 int (*get)(const DB *db, DBT *key, DBT *data, u_int flags);
130 int (*put)(const DB *db, DBT *key, const DBT *data,
133 int (*sync)(const DB *db, u_int flags);
134 int (*seq)(const DB *db, DBT *key, DBT *data, u_int flags);
139 These elements describe a database type and a set of functions performing
141 These functions take a pointer to a structure as returned by
143 and sometimes one or more pointers to key/data structures and a flag value.
146 The type of the underlying access method (and file format).
149 A pointer to a routine to flush any cached information to disk, free any
150 allocated resources, and close the underlying file(s).
151 Since key/data pairs may be cached in memory, failing to sync the file
156 function may result in inconsistent or lost information.
158 routines return -1 on error (setting
163 A pointer to a routine to remove key/data pairs from the database.
167 may be set to the following value:
171 Delete the record referenced by the cursor.
172 The cursor must have previously been initialized.
176 routines return -1 on error (setting
178 0 on success, and 1 if the specified
183 A pointer to a routine which returns a file descriptor representative
184 of the underlying database.
185 A file descriptor referencing the same file will be returned to all
191 This file descriptor may be safely used as an argument to the
196 The file descriptor is not necessarily associated with any of the
197 underlying files used by the access method.
198 No file descriptor is available for in memory databases.
200 routines return -1 on error (setting
202 and the file descriptor on success.
205 A pointer to a routine which is the interface for keyed retrieval from
207 The address and length of the data associated with the specified
209 are returned in the structure referenced by
212 routines return -1 on error (setting
214 0 on success, and 1 if the
219 A pointer to a routine to store key/data pairs in the database.
223 may be set to one of the following values:
227 Replace the key/data pair referenced by the cursor.
228 The cursor must have previously been initialized.
231 Append the data immediately after the data referenced by
233 creating a new key/data pair.
234 The record number of the appended key/data pair is returned in the
237 (Applicable only to the DB_RECNO access method.)
240 Insert the data immediately before the data referenced by
242 creating a new key/data pair.
243 The record number of the inserted key/data pair is returned in the
246 (Applicable only to the DB_RECNO access method.)
249 Enter the new key/data pair only if the key does not previously exist.
252 Store the key/data pair, setting or initializing the position of the
253 cursor to reference it.
254 (Applicable only to the DB_BTREE and DB_RECNO access methods.)
257 R_SETCURSOR is available only for the DB_BTREE and DB_RECNO access
258 methods because it implies that the keys have an inherent order
259 which does not change.
261 R_IAFTER and R_IBEFORE are available only for the DB_RECNO
262 access method because they each imply that the access method is able to
264 This is only true if the keys are ordered and independent, record numbers
267 The default behavior of the
269 routines is to enter the new key/data pair, replacing any previously
273 routines return -1 on error (setting
275 0 on success, and 1 if the R_NOOVERWRITE
277 was set and the key already exists in the file.
280 A pointer to a routine which is the interface for sequential
281 retrieval from the database.
282 The address and length of the key are returned in the structure
285 and the address and length of the data are returned in the
290 Sequential key/data pair retrieval may begin at any time, and the
291 position of the ``cursor'' is not affected by calls to the
298 Modifications to the database during a sequential scan will be reflected
299 in the scan, i.e. records inserted behind the cursor will not be returned
300 while records inserted in front of the cursor will be returned.
304 be set to one of the following values:
308 The data associated with the specified key is returned.
309 This differs from the
311 routines in that it sets or initializes the cursor to the location of
313 (Note, for the DB_BTREE access method, the returned key is not necessarily an
314 exact match for the specified key.
315 The returned key is the smallest key greater than or equal to the specified
316 key, permitting partial key matches and range searches.)
319 The first key/data pair of the database is returned, and the cursor
320 is set or initialized to reference it.
323 The last key/data pair of the database is returned, and the cursor
324 is set or initialized to reference it.
325 (Applicable only to the DB_BTREE and DB_RECNO access methods.)
328 Retrieve the key/data pair immediately after the cursor.
329 If the cursor is not yet set, this is the same as the R_FIRST flag.
332 Retrieve the key/data pair immediately before the cursor.
333 If the cursor is not yet set, this is the same as the R_LAST flag.
334 (Applicable only to the DB_BTREE and DB_RECNO access methods.)
337 R_LAST and R_PREV are available only for the DB_BTREE and DB_RECNO
338 access methods because they each imply that the keys have an inherent
339 order which does not change.
342 routines return -1 on error (setting
344 0 on success and 1 if there are no key/data pairs less than or greater
345 than the specified or current key.
346 If the DB_RECNO access method is being used, and if the database file
347 is a character special file and no complete key/data pairs are currently
353 A pointer to a routine to flush any cached information to disk.
354 If the database is in memory only, the
356 routine has no effect and will always succeed.
358 The flag value may be set to the following value:
362 If the DB_RECNO access method is being used, this flag causes
363 the sync routine to apply to the btree file which underlies the
364 recno file, not the recno file itself.
369 manual page for more information.)
373 routines return -1 on error (setting
377 Access to all file types is based on key/data pairs.
378 Both keys and data are represented by the following data structure:
388 The elements of the DBT structure are defined as follows:
391 A pointer to a byte string.
394 The length of the byte string.
396 Key and data byte strings may reference strings of essentially unlimited
397 length although any two of them must fit into available memory at the same
399 It should be noted that the access methods provide no guarantees about
400 byte string alignment.
404 routine may fail and set
406 for any of the errors specified for the library routines
413 A file is incorrectly formatted.
416 A parameter has been specified (hash function, pad byte etc.) that is
417 incompatible with the current file specification or which is not
418 meaningful for the function (for example, use of the cursor without
419 prior initialization) or there is a mismatch between the version
420 number of file and the software.
424 routines may fail and set
426 for any of the errors specified for the library routines
440 routines may fail and set
442 for any of the errors specified for the library routines
451 routines will fail and set
453 to ENOENT for in memory databases.
457 routines may fail and set
459 for any of the errors specified for the library routine
467 .IR "LIBTP: Portable, Modular Transactions for UNIX" ,
468 Margo Seltzer, Michael Olson, USENIX proceedings, Winter 1992.
470 The typedef DBT is a mnemonic for ``data base thang'', and was used
471 because noone could think of a reasonable name that wasn't already used.
473 The file descriptor interface is a kluge and will be deleted in a
474 future version of the interface.
476 None of the access methods provide any form of concurrent access,
477 locking, or transactions.