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RECNO(3) Linux Programmer's Manual RECNO(3)
recno - record number database access method
#include <sys/types.h>
#include <db.h>
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.
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.
Only big and little endian byte order is supported.
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.
This page is part of release 3.32 of the Linux man-pages project. A
description of the project, and information about reporting bugs, can be found
at http://www.kernel.org/doc/man-pages/.
4.4 Berkeley Distribution 1994-08-18 RECNO(3)
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