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229 lines
6.6 KiB
Groff
229 lines
6.6 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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.\" 4. 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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.\" @(#)recno.3 8.5 (Berkeley) 8/18/94
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.\" $FreeBSD$
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.\"
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.Dd August 18, 1994
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.Dt RECNO 3
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.Os
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.Sh NAME
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.Nm recno
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.Nd "record number database access method"
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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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.Sh DESCRIPTION
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The routine
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.Fn dbopen
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is the library interface to database files.
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One of the supported file formats is record number files.
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The general description of the database access methods is in
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.Xr dbopen 3 ,
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this manual page describes only the
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.Nm
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specific information.
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.Pp
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The record number data structure is either variable or fixed-length
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records stored in a flat-file format, accessed by the logical record
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number.
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The existence of record number five implies the existence of records
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one through four, and the deletion of record number one causes
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record number five to be renumbered to record number four, as well
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as the cursor, if positioned after record number one, to shift down
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one record.
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.Pp
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The
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.Nm
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access method specific data structure provided to
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.Fn dbopen
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is defined in the
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.In db.h
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include file as follows:
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.Bd -literal
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typedef struct {
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u_long flags;
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u_int cachesize;
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u_int psize;
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int lorder;
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size_t reclen;
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u_char bval;
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char *bfname;
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} RECNOINFO;
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.Ed
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.Pp
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The elements of this structure are defined as follows:
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.Bl -tag -width indent
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.It Va flags
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The flag value is specified by
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.Em or Ns 'ing
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any of the following values:
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.Bl -tag -width indent
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.It Dv R_FIXEDLEN
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The records are fixed-length, not byte delimited.
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The structure element
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.Va reclen
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specifies the length of the record, and the structure element
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.Va bval
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is used as the pad character.
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Any records, inserted into the database, that are less than
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.Va reclen
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bytes long are automatically padded.
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.It Dv R_NOKEY
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In the interface specified by
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.Fn dbopen ,
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the sequential record retrieval fills in both the caller's key and
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data structures.
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If the
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.Dv R_NOKEY
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flag is specified, the
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.Em cursor
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routines are not required to fill in the key structure.
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This permits applications to retrieve records at the end of files without
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reading all of the intervening records.
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.It Dv R_SNAPSHOT
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This flag requires that a snapshot of the file be taken when
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.Fn dbopen
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is called, instead of permitting any unmodified records to be read from
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the original file.
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.El
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.It Va cachesize
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A suggested maximum size, in bytes, of the memory cache.
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This value is
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.Em only
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advisory, and the access method will allocate more memory rather than fail.
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If
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.Va cachesize
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is 0 (no size is specified) a default cache is used.
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.It Va psize
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The
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.Nm
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access method stores the in-memory copies of its records
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in a btree.
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This value is the size (in bytes) of the pages used for nodes in that tree.
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If
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.Va psize
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is 0 (no page size is specified) a page size is chosen based on the
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underlying file system I/O block size.
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See
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.Xr btree 3
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for more information.
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.It Va lorder
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The byte order for integers in the stored database metadata.
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The number should represent the order as an integer; for example,
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big endian order would be the number 4,321.
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If
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.Va lorder
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is 0 (no order is specified) the current host order is used.
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.It Va reclen
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The length of a fixed-length record.
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.It Va bval
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The delimiting byte to be used to mark the end of a record for
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variable-length records, and the pad character for fixed-length
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records.
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If no value is specified, newlines
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.Pq Dq \en
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are used to mark the end
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of variable-length records and fixed-length records are padded with
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spaces.
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.It Va bfname
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The
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.Nm
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access method stores the in-memory copies of its records
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in a btree.
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If
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.Va bfname
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is
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.No non\- Ns Dv NULL ,
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it specifies the name of the btree file,
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as if specified as the file name for a
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.Fn dbopen
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of a btree file.
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.El
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.Pp
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The data part of the key/data pair used by the
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.Nm
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access method
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is the same as other access methods.
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The key is different.
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The
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.Va data
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field of the key should be a pointer to a memory location of type
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.Ft recno_t ,
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as defined in the
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.In db.h
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include file.
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This type is normally the largest unsigned integral type available to
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the implementation.
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The
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.Va size
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field of the key should be the size of that type.
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.Pp
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Because there can be no meta-data associated with the underlying
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.Nm
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access method files, any changes made to the default values
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(e.g.\& fixed record length or byte separator value) must be explicitly
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specified each time the file is opened.
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.Pp
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In the interface specified by
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.Fn dbopen ,
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using the
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.Va put
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interface to create a new record will cause the creation of multiple,
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empty records if the record number is more than one greater than the
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largest record currently in the database.
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.Sh ERRORS
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The
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.Nm
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access method routines may fail and set
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.Va errno
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for any of the errors specified for the library routine
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.Xr dbopen 3
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or the following:
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.Bl -tag -width Er
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.It Bq Er EINVAL
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An attempt was made to add a record to a fixed-length database that
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was too large to fit.
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.El
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.Sh SEE ALSO
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.Xr btree 3 ,
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.Xr dbopen 3 ,
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.Xr hash 3 ,
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.Xr mpool 3
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.Rs
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.%T "Document Processing in a Relational Database System"
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.%A Michael Stonebraker
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.%A Heidi Stettner
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.%A Joseph Kalash
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.%A Antonin Guttman
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.%A Nadene Lynn
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.%R "Memorandum No. UCB/ERL M82/32"
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.%D May 1982
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.Re
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.Sh BUGS
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Only big and little endian byte order is supported.
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