NAME
recno - record number database access method
SYNOPSIS
#include <sys/types.h>
#include <db.h>
DESCRIPTION
The routine dbopen(3) 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(3)
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 database, that
are less than reclen bytes long are automatically padded.
R_NOKEY
In the interface specified by dbopen(3), 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(3) 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 filename for a
dbopen(3) 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 th <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 metadata 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(3), 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.
BUGS
Only big and little endian byte order is supported.
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.
COLOPHON
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