535 lines
14 KiB
Groff
535 lines
14 KiB
Groff
.\" $NetBSD: dbopen.3,v 1.18 2010/03/22 19:30:53 joerg Exp $
|
|
.\"
|
|
.\" 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. 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
|
|
.\"
|
|
.Dd April 17, 2003
|
|
.Dt DBOPEN 3
|
|
.Os
|
|
.Sh NAME
|
|
.Nm dbopen ,
|
|
.Nm db
|
|
.Nd database access methods
|
|
.Sh SYNOPSIS
|
|
.In sys/types.h
|
|
.In limits.h
|
|
.In db.h
|
|
.In fcntl.h
|
|
.Ft DB *
|
|
.Fn dbopen "const char *file" "int flags" "mode_t mode" \
|
|
"DBTYPE type" "const void *openinfo"
|
|
.Sh DESCRIPTION
|
|
.Nm
|
|
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
|
|
.Xr btree 3 ,
|
|
.Xr hash 3 ,
|
|
and
|
|
.Xr recno 3 .
|
|
.Pp
|
|
.Nm
|
|
opens
|
|
.Fa file
|
|
for reading and/or writing.
|
|
Files never intended to be preserved on disk may be created by setting
|
|
the file parameter to
|
|
.Dv NULL .
|
|
.Pp
|
|
The
|
|
.Fa flags
|
|
and
|
|
.Fa mode
|
|
arguments are as specified to the
|
|
.Xr open 2
|
|
routine, however, only the
|
|
.Dv O_CREAT ,
|
|
.Dv O_EXCL ,
|
|
.Dv O_EXLOCK ,
|
|
.Dv O_NONBLOCK ,
|
|
.Dv O_RDONLY ,
|
|
.Dv O_RDWR ,
|
|
.Dv O_SHLOCK ,
|
|
and
|
|
.Dv O_TRUNC
|
|
flags are meaningful.
|
|
(Note, opening a database file
|
|
.Dv O_WRONLY
|
|
is not possible.)
|
|
.\"Three additional options may be specified by or'ing
|
|
.\"them into the
|
|
.\".Fa flags
|
|
.\"argument.
|
|
.\".Pp
|
|
.\".Dv 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.
|
|
.\".Pp
|
|
.\".Dv DB_SHMEM
|
|
.\"Place the underlying memory pool used by the database in shared
|
|
.\"memory.
|
|
.\"Necessary for concurrent access.
|
|
.\".Pp
|
|
.\".Dv DB_TXN
|
|
.\"Support transactions in the database.
|
|
.\"The
|
|
.\".Dv DB_LOCK
|
|
.\"and
|
|
.\".Dv DB_SHMEM
|
|
.\"flags must be set as well.
|
|
.Pp
|
|
The
|
|
.Fa type
|
|
argument is of type
|
|
.Vt DBTYPE
|
|
(as defined in the
|
|
.In db.h
|
|
include file) and may be set to
|
|
.Dv DB_BTREE ,
|
|
.Dv DB_HASH ,
|
|
or
|
|
.Dv DB_RECNO .
|
|
.Pp
|
|
The
|
|
.Fa openinfo
|
|
argument is a pointer to an access method specific structure described
|
|
in the access method's manual page.
|
|
If
|
|
.Fa openinfo
|
|
is
|
|
.Dv NULL ,
|
|
each access method will use defaults appropriate for the system and
|
|
the access method.
|
|
.Pp
|
|
.Nm
|
|
returns a pointer to a DB structure on success and
|
|
.Dv NULL
|
|
on error.
|
|
The DB structure is defined in the
|
|
.In db.h
|
|
include file, and contains at least the following fields:
|
|
.Bd -literal
|
|
typedef struct {
|
|
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,
|
|
u_int flags);
|
|
int (*sync)(const DB *db, u_int flags);
|
|
int (*seq)(const DB *db, DBT *key, DBT *data, u_int flags);
|
|
} DB;
|
|
.Ed
|
|
.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
|
|
.Nm ,
|
|
and sometimes one or more pointers to key/data structures and a flag
|
|
value.
|
|
.Bl -tag -width closex
|
|
.It Fa type
|
|
The type of the underlying access method (and file format).
|
|
.It Fa 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
|
|
.Fa close
|
|
or
|
|
.Fa sync
|
|
function may result in inconsistent or lost information.
|
|
.Fa close
|
|
routines return \-1 on error (setting
|
|
.Va errno )
|
|
and 0 on success.
|
|
.It Fa del
|
|
A pointer to a routine to remove key/data pairs from the database.
|
|
.Pp
|
|
The parameter
|
|
.Fa flag
|
|
may be set to the following value:
|
|
.Bl -tag -width R_CURSORX
|
|
.It Dv R_CURSOR
|
|
Delete the record referenced by the cursor.
|
|
The cursor must have previously been initialized.
|
|
.El
|
|
.Pp
|
|
.Fa delete
|
|
routines return \-1 on error (setting
|
|
.Va errno ) ,
|
|
0 on success, and 1 if the specified
|
|
.Fa key
|
|
was not in the file.
|
|
.It Fa 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
|
|
.Nm
|
|
with the same
|
|
.Fa file
|
|
name.
|
|
This file descriptor may be safely used as an argument to the
|
|
.Xr fcntl 2
|
|
and
|
|
.Xr 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.
|
|
.Fa fd
|
|
routines return \-1 on error (setting
|
|
.Va errno ) ,
|
|
and the file descriptor on success.
|
|
.It Fa 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
|
|
.Fa key
|
|
are returned in the structure referenced by
|
|
.Fa data .
|
|
.Fa get
|
|
routines return \-1 on error (setting
|
|
.Va errno ) ,
|
|
0 on success, and 1 if the
|
|
.Fa key
|
|
was not in the file.
|
|
.It Fa put
|
|
A pointer to a routine to store key/data pairs in the database.
|
|
.Pp
|
|
The parameter
|
|
.Fa flag
|
|
may be set to one of the following values:
|
|
.Bl -tag -width R_NOOVERWRITEX
|
|
.It Dv R_CURSOR
|
|
Replace the key/data pair referenced by the cursor.
|
|
The cursor must have previously been initialized.
|
|
.It Dv R_IAFTER
|
|
Append the data immediately after the data referenced by
|
|
.Fa key ,
|
|
creating a new key/data pair.
|
|
The record number of the appended key/data pair is returned in the
|
|
.Fa key
|
|
structure.
|
|
(Applicable only to the
|
|
.Dv DB_RECNO
|
|
access method.)
|
|
.It Dv R_IBEFORE
|
|
Insert the data immediately before the data referenced by
|
|
.Fa key ,
|
|
creating a new key/data pair.
|
|
The record number of the inserted key/data pair is returned in the
|
|
.Fa key
|
|
structure.
|
|
(Applicable only to the
|
|
.Dv DB_RECNO
|
|
access method.)
|
|
.It Dv R_NOOVERWRITE
|
|
Enter the new key/data pair only if the key does not previously
|
|
exist.
|
|
.It Dv R_SETCURSOR
|
|
Store the key/data pair, setting or initializing the position of the
|
|
cursor to reference it.
|
|
(Applicable only to the
|
|
.Dv DB_BTREE
|
|
and
|
|
.Dv DB_RECNO
|
|
access methods.)
|
|
.El
|
|
.Pp
|
|
.Dv R_SETCURSOR
|
|
is available only for the
|
|
.Dv DB_BTREE
|
|
and
|
|
.Dv DB_RECNO
|
|
access methods because it implies that the keys have an inherent order
|
|
which does not change.
|
|
.Pp
|
|
.Dv R_IAFTER
|
|
and
|
|
.Dv R_IBEFORE
|
|
are available only for the
|
|
.Dv 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.
|
|
.Pp
|
|
The default behavior of the
|
|
.Fa put
|
|
routines is to enter the new key/data pair, replacing any previously
|
|
existing key.
|
|
.Pp
|
|
.Fa put
|
|
routines return \-1 on error (setting
|
|
.Va errno ) ,
|
|
0 on success, and 1 if the
|
|
.Dv R_NOOVERWRITE
|
|
.Fa flag
|
|
was set and the key already exists in the file.
|
|
.It Fa 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
|
|
.Fa key ,
|
|
and the address and length of the data are returned in the
|
|
structure referenced by
|
|
.Fa data .
|
|
.Pp
|
|
Sequential key/data pair retrieval may begin at any time, and the
|
|
position of the
|
|
.Dq cursor
|
|
is not affected by calls to the
|
|
.Fa del ,
|
|
.Fa get ,
|
|
.Fa put ,
|
|
or
|
|
.Fa 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.
|
|
.Pp
|
|
The flag value
|
|
.Em must
|
|
be set to one of the following values:
|
|
.Bl -tag -width R_CURSORX
|
|
.It Dv R_CURSOR
|
|
The data associated with the specified key is returned.
|
|
This differs from the
|
|
.Fa get
|
|
routines in that it sets or initializes the cursor to the location of
|
|
the key as well.
|
|
(Note, for the
|
|
.Dv 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.)
|
|
.It Dv R_FIRST
|
|
The first key/data pair of the database is returned, and the cursor
|
|
is set or initialized to reference it.
|
|
.It Dv 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
|
|
.Dv DB_BTREE
|
|
and
|
|
.Dv DB_RECNO
|
|
access methods.)
|
|
.It Dv R_NEXT
|
|
Retrieve the key/data pair immediately after the cursor.
|
|
If the cursor is not yet set, this is the same as the
|
|
.Dv R_FIRST
|
|
flag.
|
|
.It Dv R_PREV
|
|
Retrieve the key/data pair immediately before the cursor.
|
|
If the cursor is not yet set, this is the same as the
|
|
.Dv R_LAST
|
|
flag.
|
|
(Applicable only to the
|
|
.Dv DB_BTREE
|
|
and
|
|
.Dv DB_RECNO
|
|
access methods.)
|
|
.El
|
|
.Pp
|
|
.Dv R_LAST
|
|
and
|
|
.Dv R_PREV
|
|
are available only for the
|
|
.Dv DB_BTREE
|
|
and
|
|
.Dv DB_RECNO
|
|
access methods because they each imply that the keys have an inherent
|
|
order which does not change.
|
|
.Pp
|
|
.Fa seq
|
|
routines return \-1 on error (setting
|
|
.Va 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
|
|
.Dv 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
|
|
.Fa seq
|
|
routines return 2.
|
|
.It Fa sync
|
|
A pointer to a routine to flush any cached information to disk.
|
|
If the database is in memory only, the
|
|
.Fa sync
|
|
routine has no effect and will always succeed.
|
|
.Pp
|
|
The flag value may be set to the following value:
|
|
.Bl -tag -width ".Dv R_RECNOSYNC"
|
|
.It Dv R_RECNOSYNC
|
|
If the
|
|
.Dv 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
|
|
.Fa bfname
|
|
field of the
|
|
.Xr recno 3
|
|
manual page for more information.)
|
|
.El
|
|
.Pp
|
|
.Fa sync
|
|
routines return \-1 on error (setting
|
|
.Va errno )
|
|
and 0 on success.
|
|
.El
|
|
.Ss 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:
|
|
.Bd -literal
|
|
typedef struct {
|
|
void *data;
|
|
size_t size;
|
|
} DBT;
|
|
.Ed
|
|
.Pp
|
|
The elements of the DBT structure are defined as follows:
|
|
.Bl -tag -width datax
|
|
.It Fa data
|
|
A pointer to a byte string.
|
|
.It Fa size
|
|
The length of the byte string.
|
|
.El
|
|
.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
|
|
.Nm
|
|
routine may fail and set
|
|
.Va errno
|
|
for any of the errors specified for the library routines
|
|
.Xr open 2
|
|
and
|
|
.Xr malloc 3
|
|
or the following:
|
|
.Bl -tag -width Er
|
|
.It Er EFTYPE
|
|
A file is incorrectly formatted.
|
|
.It Er 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.
|
|
.It Er EFBIG
|
|
The key could not be inserted due to limitations in the DB file format
|
|
(e.g., a hash database was out of overflow pages).
|
|
.El
|
|
.Pp
|
|
The
|
|
.Fa close
|
|
routines may fail and set
|
|
.Va errno
|
|
for any of the errors specified for the library routines
|
|
.Xr close 2 ,
|
|
.Xr read 2 ,
|
|
.Xr write 2 ,
|
|
.Xr free 3 ,
|
|
or
|
|
.Xr fsync 2 .
|
|
.Pp
|
|
The
|
|
.Fa del ,
|
|
.Fa get ,
|
|
.Fa put ,
|
|
and
|
|
.Fa seq
|
|
routines may fail and set
|
|
.Va errno
|
|
for any of the errors specified for the library routines
|
|
.Xr read 2 ,
|
|
.Xr write 2 ,
|
|
.Xr free 3 ,
|
|
or
|
|
.Xr malloc 3 .
|
|
.Pp
|
|
The
|
|
.Fa fd
|
|
routines will fail and set
|
|
.Va errno
|
|
to
|
|
.Er ENOENT
|
|
for in memory databases.
|
|
.Pp
|
|
The
|
|
.Fa sync
|
|
routines may fail and set
|
|
.Va errno
|
|
for any of the errors specified for the library routine
|
|
.Xr fsync 2 .
|
|
.Sh SEE ALSO
|
|
.Xr btree 3 ,
|
|
.Xr hash 3 ,
|
|
.Xr mpool 3 ,
|
|
.Xr recno 3
|
|
.Pp
|
|
.Rs
|
|
.%T "LIBTP: Portable, Modular Transactions for UNIX"
|
|
.%A Margo Seltzer
|
|
.%A Michael Olson
|
|
.%J USENIX proceedings
|
|
.%D Winter 1992
|
|
.Re
|
|
.Sh BUGS
|
|
The typedef DBT is a mnemonic for
|
|
.Dq data base thang ,
|
|
and was used because no one 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.
|