RECNO(3)RECNO(3)NAMErecno - 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 fol-
lows:
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
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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
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RECNO(3)RECNO(3)
largest unsigned integral type available to the implemen-
tation. 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 sepa-
rator value) must be explicitly specified each time the
file is opened.
In the interface specified by dbopen, using the put inter-
face 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 ALSObtree(3)dbopen(3), hash(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.
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