RECNO(3) UNIX System V (August 18, 1994) RECNO(3)
NAME
recno - record number database access method
SYNOPSIS
#include <sys/types.h>
#include <db.h>
DESCRIPTION
The routine dbopen is the library interface to database
files. One of the supported file formats is record number
files. The general description of the database access
methods is in dbopen(3), this manual page describes only the
recno specific information.
The record number data structure is either variable or
fixed-length records stored in a flat-file format, accessed
by the logical record number. The existence of record
number five implies the existence of records one through
four, and the deletion of record number one causes record
number five to be renumbered to record number four, as well
as the cursor, if positioned after record number one, to
shift down one record.
The recno access method specific data structure provided to
dbopen is defined in the <db.h> include file as follows:
typedef struct {
u_long flags;
u_int cachesize;
u_int psize;
int lorder;
size_t reclen;
u_char bval;
char *bfname;
} RECNOINFO;
The elements of this structure are defined as follows:
flags
The flag value is specified by or'ing any of the
following values:
R_FIXEDLEN
The records are fixed-length, not byte delimited.
The structure element reclen specifies the length
of the record, and the structure element bval is
used as the pad character. Any records, inserted
into the database, that are less than reclen bytes
long are automatically padded.
R_NOKEY
In the interface specified by dbopen, the
sequential record retrieval fills in both the
caller's key and data structures. If the R_NOKEY
flag is specified, the cursor routines are not
required to fill in the key structure. This
permits applications to retrieve records at the
end of files without reading all of the
intervening records.
R_SNAPSHOT
This flag requires that a snapshot of the file be
taken when dbopen is called, instead of permitting
any unmodified records to be read from the
original file.
cachesize
A suggested maximum size, in bytes, of the memory
cache. This value is only advisory, and the access
method will allocate more memory rather than fail. If
cachesize is 0 (no size is specified) a default cache
is used.
psize
The recno access method stores the in-memory copies of
its records in a btree. This value is the size (in
bytes) of the pages used for nodes in that tree. If
psize is 0 (no page size is specified) a page size is
chosen based on the underlying file system I/O block
size. See btree(3) for more information.
lorder
The byte order for integers in the stored database
metadata. The number should represent the order as an
integer; for example, big endian order would be the
number 4,321. If lorder is 0 (no order is specified)
the current host order is used.
reclen
The length of a fixed-length record.
bval The delimiting byte to be used to mark the end of a
record for variable-length records, and the pad
character for fixed-length records. If no value is
specified, newlines (``\n'') are used to mark the end
of variable-length records and fixed-length records are
padded with spaces.
bfname
The recno access method stores the in-memory copies of
its records in a btree. If bfname is non-NULL, it
specifies the name of the btree file, as if specified
as the file name for a dbopen of a btree file.
The data part of the key/data pair used by the recno access
method is the same as other access methods. The key is
different. The data field of the key should be a pointer to
a memory location of type recno_t, as defined in the <db.h>
include file. This type is normally the largest unsigned
integral type available to the implementation. The size
field of the key should be the size of that type.
Because there can be no meta-data associated with the
underlying recno access method files, any changes made to
the default values (e.g. fixed record length or byte
separator value) must be explicitly specified each time the
file is opened.
In the interface specified by dbopen, using the put
interface to create a new record will cause the creation of
multiple, empty records if the record number is more than
one greater than the largest record currently in the
database.
ERRORS
The recno access method routines may fail and set errno for
any of the errors specified for the library routine
dbopen(3) or the following:
[EINVAL]
An attempt was made to add a record to a fixed-length
database that was too large to fit.
SEE ALSO
btree(3) dbopen(3), hash(3), mpool(3),
Document Processing in a Relational Database System, Michael
Stonebraker, Heidi Stettner, Joseph Kalash, Antonin Guttman,
Nadene Lynn, Memorandum No. UCB/ERL M82/32, May 1982.
BUGS
Only big and little endian byte order is supported.
Page 3 (printed 4/30/98)