RECNO(3) BSD Programmer's Manual RECNO(3)NAMErecno - record number database access method
SYNOPSIS
#include <sys/types.h>
#include <db.h>
DESCRIPTION
The dbopen() routine is the library interface to database files. One of
the supported file formats is record number files. The general descrip-
tion 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 {
unsigned long flags;
unsigned int cachesize;
unsigned int psize;
int lorder;
size_t reclen;
unsigned 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 data-
base, that are less than reclen bytes long are au-
tomatically padded.
R_NOKEY In the interface specified by dbopen(), the sequen-
tial record retrieval fills in both the caller's key
and data structures. If the R_NOKEY flag is speci-
fied, the cursor routines are not required to fill in
the key structure. This permits applications to re-
trieve 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(3) file, as if specified as the file name for a
dbopen(3) of a btree(3) 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 loca-
tion 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 ex-
plicitly 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 ALSObtree(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.
BUGS
Only big and little endian byte order is supported.
MirOS BSD #10-current August 18, 1994 1
