diff options
Diffstat (limited to 'man3/dbopen.3')
| -rw-r--r-- | man3/dbopen.3 | 476 |
1 files changed, 476 insertions, 0 deletions
diff --git a/man3/dbopen.3 b/man3/dbopen.3 new file mode 100644 index 000000000..47277c874 --- /dev/null +++ b/man3/dbopen.3 @@ -0,0 +1,476 @@ +.\" Copyright (c) 1990, 1993 +.\" The Regents of the University of California. All rights reserved. +.\" +.\" Redistribution and use in source and binary forms, with or without +.\" modification, are permitted provided that the following conditions +.\" are met: +.\" 1. Redistributions of source code must retain the above copyright +.\" notice, this list of conditions and the following disclaimer. +.\" 2. Redistributions in binary form must reproduce the above copyright +.\" notice, this list of conditions and the following disclaimer in the +.\" documentation and/or other materials provided with the distribution. +.\" 3. All advertising materials mentioning features or use of this software +.\" must display the following acknowledgement: +.\" This product includes software developed by the University of +.\" California, Berkeley and its contributors. +.\" 4. Neither the name of the University nor the names of its contributors +.\" may be used to endorse or promote products derived from this software +.\" without specific prior written permission. +.\" +.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND +.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE +.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE +.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE +.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL +.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS +.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) +.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT +.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY +.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF +.\" SUCH DAMAGE. +.\" +.\" @(#)dbopen.3 8.5 (Berkeley) 1/2/94 +.\" +.TH DBOPEN 3 1994-01-02 +.UC 7 +.SH NAME +dbopen \- database access methods +.SH SYNOPSIS +.nf +.ft B +#include <sys/types.h> +#include <limits.h> +#include <db.h> + +DB * +dbopen(const char *file, int flags, int mode, DBTYPE type, +.ti +5 +const void *openinfo); +.ft R +.fi +.SH DESCRIPTION +.IR Dbopen +is the library interface to database files. +The supported file formats are btree, hashed and UNIX file oriented. +The btree format is a representation of a sorted, balanced tree structure. +The hashed format is an extensible, dynamic hashing scheme. +The flat-file format is a byte stream file with fixed or variable length +records. +The formats and file format specific information are described in detail +in their respective manual pages +.IR btree (3), +.IR hash (3) +and +.IR recno (3). +.PP +Dbopen opens +.I file +for reading and/or writing. +Files never intended to be preserved on disk may be created by setting +the file parameter to NULL. +.PP +The +.I flags +and +.I mode +arguments are as specified to the +.IR open (2) +routine, however, only the O_CREAT, O_EXCL, O_EXLOCK, O_NONBLOCK, +O_RDONLY, O_RDWR, O_SHLOCK and O_TRUNC flags are meaningful. +(Note, opening a database file O_WRONLY is not possible.) +.\"Three additional options may be specified by +.\".IR or 'ing +.\"them into the +.\".I flags +.\"argument. +.\".TP +.\"DB_LOCK +.\"Do the necessary locking in the database to support concurrent access. +.\"If concurrent access isn't needed or the database is read-only this +.\"flag should not be set, as it tends to have an associated performance +.\"penalty. +.\".TP +.\"DB_SHMEM +.\"Place the underlying memory pool used by the database in shared +.\"memory. +.\"Necessary for concurrent access. +.\".TP +.\"DB_TXN +.\"Support transactions in the database. +.\"The DB_LOCK and DB_SHMEM flags must be set as well. +.PP +The +.I type +argument is of type DBTYPE (as defined in the <db.h> include file) and +may be set to DB_BTREE, DB_HASH or DB_RECNO. +.PP +The +.I openinfo +argument is a pointer to an access method specific structure described +in the access method's manual page. +If +.I openinfo +is NULL, each access method will use defaults appropriate for the system +and the access method. +.PP +.I Dbopen +returns a pointer to a DB structure on success and NULL on error. +The DB structure is defined in the <db.h> include file, and contains at +least the following fields: +.sp +.nf +typedef struct { +.RS +DBTYPE type; +int (*close)(const DB *db); +int (*del)(const DB *db, const DBT *key, u_int flags); +int (*fd)(const DB *db); +int (*get)(const DB *db, DBT *key, DBT *data, u_int flags); +int (*put)(const DB *db, DBT *key, const DBT *data, +.ti +5 +u_int flags); +int (*sync)(const DB *db, u_int flags); +int (*seq)(const DB *db, DBT *key, DBT *data, u_int flags); +.RE +} DB; +.fi +.PP +These elements describe a database type and a set of functions performing +various actions. +These functions take a pointer to a structure as returned by +.IR dbopen , +and sometimes one or more pointers to key/data structures and a flag value. +.TP +type +The type of the underlying access method (and file format). +.TP +close +A pointer to a routine to flush any cached information to disk, free any +allocated resources, and close the underlying file(s). +Since key/data pairs may be cached in memory, failing to sync the file +with a +.I close +or +.I sync +function may result in inconsistent or lost information. +.I Close +routines return \-1 on error (setting +.IR errno ) +and 0 on success. +.TP +del +A pointer to a routine to remove key/data pairs from the database. +.IP +The parameter +.I flag +may be set to the following value: +.RS +.TP +R_CURSOR +Delete the record referenced by the cursor. +The cursor must have previously been initialized. +.RE +.IP +.I Delete +routines return \-1 on error (setting +.IR errno ), +0 on success, and 1 if the specified +.I key +was not in the file. +.TP +fd +A pointer to a routine which returns a file descriptor representative +of the underlying database. +A file descriptor referencing the same file will be returned to all +processes which call +.I dbopen +with the same +.I file +name. +This file descriptor may be safely used as an argument to the +.IR fcntl (2) +and +.IR flock (2) +locking functions. +The file descriptor is not necessarily associated with any of the +underlying files used by the access method. +No file descriptor is available for in memory databases. +.I Fd +routines return \-1 on error (setting +.IR errno ), +and the file descriptor on success. +.TP +get +A pointer to a routine which is the interface for keyed retrieval from +the database. +The address and length of the data associated with the specified +.I key +are returned in the structure referenced by +.IR data . +.I Get +routines return \-1 on error (setting +.IR errno ), +0 on success, and 1 if the +.I key +was not in the file. +.TP +put +A pointer to a routine to store key/data pairs in the database. +.IP +The parameter +.I flag +may be set to one of the following values: +.RS +.TP +R_CURSOR +Replace the key/data pair referenced by the cursor. +The cursor must have previously been initialized. +.TP +R_IAFTER +Append the data immediately after the data referenced by +.IR key , +creating a new key/data pair. +The record number of the appended key/data pair is returned in the +.I key +structure. +(Applicable only to the DB_RECNO access method.) +.TP +R_IBEFORE +Insert the data immediately before the data referenced by +.IR key , +creating a new key/data pair. +The record number of the inserted key/data pair is returned in the +.I key +structure. +(Applicable only to the DB_RECNO access method.) +.TP +R_NOOVERWRITE +Enter the new key/data pair only if the key does not previously exist. +.TP +R_SETCURSOR +Store the key/data pair, setting or initializing the position of the +cursor to reference it. +(Applicable only to the DB_BTREE and DB_RECNO access methods.) +.RE +.IP +R_SETCURSOR is available only for the DB_BTREE and DB_RECNO access +methods because it implies that the keys have an inherent order +which does not change. +.IP +R_IAFTER and R_IBEFORE are available only for the DB_RECNO +access method because they each imply that the access method is able to +create new keys. +This is only true if the keys are ordered and independent, record numbers +for example. +.IP +The default behavior of the +.I put +routines is to enter the new key/data pair, replacing any previously +existing key. +.IP +.I Put +routines return \-1 on error (setting +.IR errno ), +0 on success, and 1 if the R_NOOVERWRITE +.I flag +was set and the key already exists in the file. +.TP +seq +A pointer to a routine which is the interface for sequential +retrieval from the database. +The address and length of the key are returned in the structure +referenced by +.IR key , +and the address and length of the data are returned in the +structure referenced +by +.IR data . +.IP +Sequential key/data pair retrieval may begin at any time, and the +position of the ``cursor'' is not affected by calls to the +.IR del , +.IR get , +.IR put , +or +.I sync +routines. +Modifications to the database during a sequential scan will be reflected +in the scan, i.e. records inserted behind the cursor will not be returned +while records inserted in front of the cursor will be returned. +.IP +The flag value +.B must +be set to one of the following values: +.RS +.TP +R_CURSOR +The data associated with the specified key is returned. +This differs from the +.I get +routines in that it sets or initializes the cursor to the location of +the key as well. +(Note, for the DB_BTREE access method, the returned key is not necessarily an +exact match for the specified key. +The returned key is the smallest key greater than or equal to the specified +key, permitting partial key matches and range searches.) +.TP +R_FIRST +The first key/data pair of the database is returned, and the cursor +is set or initialized to reference it. +.TP +R_LAST +The last key/data pair of the database is returned, and the cursor +is set or initialized to reference it. +(Applicable only to the DB_BTREE and DB_RECNO access methods.) +.TP +R_NEXT +Retrieve the key/data pair immediately after the cursor. +If the cursor is not yet set, this is the same as the R_FIRST flag. +.TP +R_PREV +Retrieve the key/data pair immediately before the cursor. +If the cursor is not yet set, this is the same as the R_LAST flag. +(Applicable only to the DB_BTREE and DB_RECNO access methods.) +.RE +.IP +R_LAST and R_PREV are available only for the DB_BTREE and DB_RECNO +access methods because they each imply that the keys have an inherent +order which does not change. +.IP +.I Seq +routines return \-1 on error (setting +.IR errno ), +0 on success and 1 if there are no key/data pairs less than or greater +than the specified or current key. +If the DB_RECNO access method is being used, and if the database file +is a character special file and no complete key/data pairs are currently +available, the +.I seq +routines return 2. +.TP +sync +A pointer to a routine to flush any cached information to disk. +If the database is in memory only, the +.I sync +routine has no effect and will always succeed. +.IP +The flag value may be set to the following value: +.RS +.TP +R_RECNOSYNC +If the DB_RECNO access method is being used, this flag causes +the sync routine to apply to the btree file which underlies the +recno file, not the recno file itself. +(See the +.I bfname +field of the +.IR recno (3) +manual page for more information.) +.RE +.IP +.I Sync +routines return \-1 on error (setting +.IR errno ) +and 0 on success. +.SH "KEY/DATA PAIRS" +Access to all file types is based on key/data pairs. +Both keys and data are represented by the following data structure: +.PP +typedef struct { +.RS +void *data; +.br +size_t size; +.RE +} DBT; +.PP +The elements of the DBT structure are defined as follows: +.TP +data +A pointer to a byte string. +.TP +size +The length of the byte string. +.PP +Key and data byte strings may reference strings of essentially unlimited +length although any two of them must fit into available memory at the same +time. +It should be noted that the access methods provide no guarantees about +byte string alignment. +.SH ERRORS +The +.I dbopen +routine may fail and set +.I errno +for any of the errors specified for the library routines +.IR open (2) +and +.IR malloc (3) +or the following: +.TP +[EFTYPE] +A file is incorrectly formatted. +.TP +[EINVAL] +A parameter has been specified (hash function, pad byte etc.) that is +incompatible with the current file specification or which is not +meaningful for the function (for example, use of the cursor without +prior initialization) or there is a mismatch between the version +number of file and the software. +.PP +The +.I close +routines may fail and set +.I errno +for any of the errors specified for the library routines +.IR close (2), +.IR read (2), +.IR write (2), +.IR free (3), +or +.IR fsync (2). +.PP +The +.IR del , +.IR get , +.I put +and +.I seq +routines may fail and set +.I errno +for any of the errors specified for the library routines +.IR read (2), +.IR write (2), +.IR free (3) +or +.IR malloc (3). +.PP +The +.I fd +routines will fail and set +.I errno +to ENOENT for in memory databases. +.PP +The +.I sync +routines may fail and set +.I errno +for any of the errors specified for the library routine +.IR fsync (2). +.SH "SEE ALSO" +.IR btree (3), +.IR hash (3), +.IR mpool (3), +.IR recno (3) +.sp +.IR "LIBTP: Portable, Modular Transactions for UNIX" , +Margo Seltzer, Michael Olson, USENIX proceedings, Winter 1992. +.SH BUGS +The typedef DBT is a mnemonic for ``data base thang'', and was used +because noone could think of a reasonable name that wasn't already used. +.PP +The file descriptor interface is a kludge and will be deleted in a +future version of the interface. +.PP +None of the access methods provide any form of concurrent access, +locking, or transactions. |