fbbd9655e5
Renumber cluase 4 to 3, per what everybody else did when BSD granted them permission to remove clause 3. My insistance on keeping the same numbering for legal reasons is too pedantic, so give up on that point. Submitted by: Jan Schaumann <jschauma@stevens.edu> Pull Request: https://github.com/freebsd/freebsd/pull/96
547 lines
14 KiB
Groff
547 lines
14 KiB
Groff
.\" Copyright (c) 1990, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)dbopen.3 8.5 (Berkeley) 1/2/94
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.\" $FreeBSD$
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.\"
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.Dd September 10, 2010
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.Dt DBOPEN 3
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.Os
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.Sh NAME
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.Nm dbopen
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.Nd "database access methods"
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.Sh SYNOPSIS
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.In sys/types.h
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.In db.h
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.In fcntl.h
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.In limits.h
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.Ft DB *
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.Fn dbopen "const char *file" "int flags" "int mode" "DBTYPE type" "const void *openinfo"
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.Sh DESCRIPTION
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The
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.Fn dbopen
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function
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is the library interface to database files.
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The supported file formats are btree, hashed and UNIX file oriented.
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The btree format is a representation of a sorted, balanced tree structure.
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The hashed format is an extensible, dynamic hashing scheme.
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The flat-file format is a byte stream file with fixed or variable length
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records.
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The formats and file format specific information are described in detail
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in their respective manual pages
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.Xr btree 3 ,
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.Xr hash 3
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and
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.Xr recno 3 .
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.Pp
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The
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.Fn dbopen
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function
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opens
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.Fa file
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for reading and/or writing.
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Files never intended to be preserved on disk may be created by setting
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the
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.Fa file
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argument to
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.Dv NULL .
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.Pp
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The
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.Fa flags
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and
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.Fa mode
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arguments
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are as specified to the
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.Xr open 2
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routine, however, only the
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.Dv O_CREAT , O_EXCL , O_EXLOCK , O_NOFOLLOW , O_NONBLOCK ,
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.Dv O_RDONLY , O_RDWR , O_SHLOCK , O_SYNC
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and
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.Dv O_TRUNC
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flags are meaningful.
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(Note, opening a database file
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.Dv O_WRONLY
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is not possible.)
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.\"Three additional options may be specified by
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.\".Em or Ns 'ing
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.\"them into the
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.\".Fa flags
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.\"argument.
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.\".Bl -tag -width indent
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.\".It Dv DB_LOCK
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.\"Do the necessary locking in the database to support concurrent access.
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.\"If concurrent access is not needed or the database is read-only this
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.\"flag should not be set, as it tends to have an associated performance
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.\"penalty.
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.\".It Dv DB_SHMEM
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.\"Place the underlying memory pool used by the database in shared
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.\"memory.
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.\"Necessary for concurrent access.
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.\".It Dv DB_TXN
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.\"Support transactions in the database.
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.\"The
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.\".Dv DB_LOCK
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.\"and
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.\".Dv DB_SHMEM
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.\"flags must be set as well.
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.\".El
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.Pp
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The
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.Fa type
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argument is of type
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.Ft DBTYPE
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(as defined in the
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.In db.h
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include file) and
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may be set to
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.Dv DB_BTREE , DB_HASH
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or
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.Dv DB_RECNO .
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.Pp
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The
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.Fa openinfo
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argument is a pointer to an access method specific structure described
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in the access method's manual page.
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If
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.Fa openinfo
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is
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.Dv NULL ,
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each access method will use defaults appropriate for the system
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and the access method.
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.Pp
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The
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.Fn dbopen
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function
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returns a pointer to a
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.Ft DB
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structure on success and
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.Dv NULL
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on error.
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The
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.Ft DB
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structure is defined in the
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.In db.h
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include file, and contains at
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least the following fields:
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.Bd -literal
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typedef struct {
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DBTYPE type;
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int (*close)(DB *db);
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int (*del)(const DB *db, const DBT *key, u_int flags);
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int (*fd)(const DB *db);
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int (*get)(const DB *db, const DBT *key, DBT *data, u_int flags);
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int (*put)(const DB *db, DBT *key, const DBT *data,
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u_int flags);
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int (*sync)(const DB *db, u_int flags);
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int (*seq)(const DB *db, DBT *key, DBT *data, u_int flags);
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} DB;
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.Ed
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.Pp
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These elements describe a database type and a set of functions performing
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various actions.
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These functions take a pointer to a structure as returned by
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.Fn dbopen ,
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and sometimes one or more pointers to key/data structures and a flag value.
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.Bl -tag -width indent
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.It Va type
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The type of the underlying access method (and file format).
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.It Va close
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A pointer to a routine to flush any cached information to disk, free any
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allocated resources, and close the underlying file(s).
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Since key/data pairs may be cached in memory, failing to sync the file
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with a
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.Va close
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or
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.Va sync
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function may result in inconsistent or lost information.
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.Va close
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routines return -1 on error (setting
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.Va errno )
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and 0 on success.
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.It Va del
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A pointer to a routine to remove key/data pairs from the database.
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.Pp
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The
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.Fa flags
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argument
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may be set to the following value:
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.Bl -tag -width indent
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.It Dv R_CURSOR
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Delete the record referenced by the cursor.
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The cursor must have previously been initialized.
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.El
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.Pp
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.Va delete
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routines return -1 on error (setting
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.Va errno ) ,
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0 on success, and 1 if the specified
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.Fa key
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was not in the file.
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.It Va fd
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A pointer to a routine which returns a file descriptor representative
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of the underlying database.
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A file descriptor referencing the same file will be returned to all
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processes which call
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.Fn dbopen
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with the same
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.Fa file
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name.
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This file descriptor may be safely used as an argument to the
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.Xr fcntl 2
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and
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.Xr flock 2
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locking functions.
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The file descriptor is not necessarily associated with any of the
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underlying files used by the access method.
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No file descriptor is available for in memory databases.
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.Va \&Fd
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routines return -1 on error (setting
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.Va errno ) ,
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and the file descriptor on success.
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.It Va get
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A pointer to a routine which is the interface for keyed retrieval from
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the database.
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The address and length of the data associated with the specified
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.Fa key
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are returned in the structure referenced by
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.Fa data .
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.Va get
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routines return -1 on error (setting
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.Va errno ) ,
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0 on success, and 1 if the
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.Fa key
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was not in the file.
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.It Va put
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A pointer to a routine to store key/data pairs in the database.
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.Pp
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The
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.Fa flags
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argument
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may be set to one of the following values:
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.Bl -tag -width indent
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.It Dv R_CURSOR
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Replace the key/data pair referenced by the cursor.
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The cursor must have previously been initialized.
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.It Dv R_IAFTER
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Append the data immediately after the data referenced by
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.Fa key ,
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creating a new key/data pair.
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The record number of the appended key/data pair is returned in the
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.Fa key
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structure.
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(Applicable only to the
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.Dv DB_RECNO
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access method.)
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.It Dv R_IBEFORE
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Insert the data immediately before the data referenced by
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.Fa key ,
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creating a new key/data pair.
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The record number of the inserted key/data pair is returned in the
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.Fa key
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structure.
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(Applicable only to the
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.Dv DB_RECNO
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access method.)
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.It Dv R_NOOVERWRITE
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Enter the new key/data pair only if the key does not previously exist.
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.It Dv R_SETCURSOR
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Store the key/data pair, setting or initializing the position of the
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cursor to reference it.
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(Applicable only to the
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.Dv DB_BTREE
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and
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.Dv DB_RECNO
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access methods.)
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.El
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.Pp
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.Dv R_SETCURSOR
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is available only for the
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.Dv DB_BTREE
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and
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.Dv DB_RECNO
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access
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methods because it implies that the keys have an inherent order
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which does not change.
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.Pp
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.Dv R_IAFTER
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and
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.Dv R_IBEFORE
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are available only for the
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.Dv DB_RECNO
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access method because they each imply that the access method is able to
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create new keys.
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This is only true if the keys are ordered and independent, record numbers
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for example.
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.Pp
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The default behavior of the
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.Va put
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routines is to enter the new key/data pair, replacing any previously
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existing key.
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.Pp
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.Va put
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routines return -1 on error (setting
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.Va errno ) ,
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0 on success, and 1 if the
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.Dv R_NOOVERWRITE
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flag
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was set and the key already exists in the file.
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.It Va seq
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A pointer to a routine which is the interface for sequential
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retrieval from the database.
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The address and length of the key are returned in the structure
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referenced by
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.Fa key ,
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and the address and length of the data are returned in the
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structure referenced
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by
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.Fa data .
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.Pp
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Sequential key/data pair retrieval may begin at any time, and the
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position of the
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.Dq cursor
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is not affected by calls to the
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.Va del ,
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.Va get ,
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.Va put ,
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or
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.Va sync
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routines.
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Modifications to the database during a sequential scan will be reflected
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in the scan, i.e., records inserted behind the cursor will not be returned
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while records inserted in front of the cursor will be returned.
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.Pp
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The
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.Fa flags
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argument
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.Em must
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be set to one of the following values:
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.Bl -tag -width indent
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.It Dv R_CURSOR
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The data associated with the specified key is returned.
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This differs from the
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.Va get
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routines in that it sets or initializes the cursor to the location of
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the key as well.
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(Note, for the
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.Dv DB_BTREE
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access method, the returned key is not necessarily an
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exact match for the specified key.
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The returned key is the smallest key greater than or equal to the specified
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key, permitting partial key matches and range searches.)
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.It Dv R_FIRST
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The first key/data pair of the database is returned, and the cursor
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is set or initialized to reference it.
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.It Dv R_LAST
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The last key/data pair of the database is returned, and the cursor
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is set or initialized to reference it.
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(Applicable only to the
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.Dv DB_BTREE
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and
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.Dv DB_RECNO
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access methods.)
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.It Dv R_NEXT
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Retrieve the key/data pair immediately after the cursor.
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If the cursor is not yet set, this is the same as the
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.Dv R_FIRST
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flag.
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.It Dv R_PREV
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Retrieve the key/data pair immediately before the cursor.
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If the cursor is not yet set, this is the same as the
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.Dv R_LAST
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flag.
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(Applicable only to the
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.Dv DB_BTREE
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and
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.Dv DB_RECNO
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access methods.)
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.El
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.Pp
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.Dv R_LAST
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and
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.Dv R_PREV
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are available only for the
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.Dv DB_BTREE
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and
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.Dv DB_RECNO
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access methods because they each imply that the keys have an inherent
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order which does not change.
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.Pp
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.Va seq
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routines return -1 on error (setting
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.Va errno ) ,
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0 on success and 1 if there are no key/data pairs less than or greater
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than the specified or current key.
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If the
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.Dv DB_RECNO
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access method is being used, and if the database file
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is a character special file and no complete key/data pairs are currently
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available, the
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.Va seq
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routines return 2.
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.It Va sync
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A pointer to a routine to flush any cached information to disk.
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If the database is in memory only, the
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.Va sync
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routine has no effect and will always succeed.
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.Pp
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The
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.Fa flags
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argument may be set to the following value:
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.Bl -tag -width indent
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.It Dv R_RECNOSYNC
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|
If the
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.Dv DB_RECNO
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access method is being used, this flag causes
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the
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.Va sync
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routine to apply to the btree file which underlies the
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recno file, not the recno file itself.
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(See the
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.Va bfname
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field of the
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.Xr recno 3
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manual page for more information.)
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.El
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.Pp
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.Va sync
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routines return -1 on error (setting
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.Va errno )
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and 0 on success.
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.El
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.Sh "KEY/DATA PAIRS"
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Access to all file types is based on key/data pairs.
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Both keys and data are represented by the following data structure:
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.Bd -literal
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typedef struct {
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void *data;
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size_t size;
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} DBT;
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.Ed
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.Pp
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The elements of the
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.Ft DBT
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structure are defined as follows:
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.Bl -tag -width "data"
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.It Va data
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|
A pointer to a byte string.
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.It Va size
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|
The length of the byte string.
|
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.El
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.Pp
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Key and data byte strings may reference strings of essentially unlimited
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length although any two of them must fit into available memory at the same
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time.
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It should be noted that the access methods provide no guarantees about
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byte string alignment.
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.Sh ERRORS
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|
The
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.Fn dbopen
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routine may fail and set
|
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.Va errno
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|
for any of the errors specified for the library routines
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|
.Xr open 2
|
|
and
|
|
.Xr malloc 3
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|
or the following:
|
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.Bl -tag -width Er
|
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.It Bq Er EFTYPE
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|
A file is incorrectly formatted.
|
|
.It Bq Er EINVAL
|
|
An argument 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.
|
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.El
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|
.Pp
|
|
The
|
|
.Va close
|
|
routines may fail and set
|
|
.Va errno
|
|
for any of the errors specified for the library routines
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.Xr close 2 ,
|
|
.Xr read 2 ,
|
|
.Xr write 2 ,
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|
.Xr free 3 ,
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|
or
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|
.Xr fsync 2 .
|
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.Pp
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|
The
|
|
.Va del ,
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|
.Va get ,
|
|
.Va put
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|
and
|
|
.Va seq
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|
routines may fail and set
|
|
.Va errno
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|
for any of the errors specified for the library routines
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.Xr read 2 ,
|
|
.Xr write 2 ,
|
|
.Xr free 3
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|
or
|
|
.Xr malloc 3 .
|
|
.Pp
|
|
The
|
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.Va fd
|
|
routines will fail and set
|
|
.Va errno
|
|
to
|
|
.Er ENOENT
|
|
for in memory databases.
|
|
.Pp
|
|
The
|
|
.Va 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 ,
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|
.Xr mpool 3 ,
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|
.Xr recno 3
|
|
.Rs
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|
.%T "LIBTP: Portable, Modular Transactions for UNIX"
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|
.%A Margo Seltzer
|
|
.%A Michael Olson
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|
.%R "USENIX proceedings"
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|
.%D Winter 1992
|
|
.Re
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|
.Sh BUGS
|
|
The typedef
|
|
.Ft DBT
|
|
is a mnemonic for
|
|
.Dq "data base thang" ,
|
|
and was used
|
|
because noone could think of a reasonable name that was not already used.
|
|
.Pp
|
|
The file descriptor interface is a kluge 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.
|