recno - record number database access method
#include <sys/types.h>
#include <db.h>
The dbopen() routine 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 (`0)
are used to
mark the end of variable-length records and fixedlength 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.
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 fixedlength database
that was too large to fit.
btree(3), dbopen(3), hash(3), mpool(3)
Michael Stonebraker, Heidi Stettner, Joseph Kalash, Antonin
Guttman, and
Nadene Lynn, "Document Processing in a Relational Database
System",
Memorandum No. UCB/ERL M82/32, May 1982.
Only big and little endian byte order is supported.
OpenBSD 3.6 August 18, 1994
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