recno - record number database access method
#include <sys/types.h> #include <db.h>
The routine dbopen() is the library interface to database
files. One of the supported file formats is record number
(recno) 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: The
flag value is specified by ORing any of the following values:
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.
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.
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. 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. 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. 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. The length of a fixed-length
record. 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.
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 metadata associated with the
underlying recno access method files, any changes made to
the default values (for example, 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.
Only big and little endian byte order is supported.
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: An attempt was made to add a
record to a fixed-length database that was too large to
fit.
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.
recno(3)
[ Back ] |
