recno - record number database access method
#include <sys/types.h>
#include <db.h>
Note well: This page documents interfaces provided in glibc up until
version 2.1. Since version 2.2, glibc no longer provides these interfaces.
Probably, you are looking for the APIs provided by the
libdb library
instead.
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 ORing 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 filesystem 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 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 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.