recno(3)recno(3)NAMErecno - record number database access method
SYNOPSIS
#include <sys/types.h> #include <db.h>
DESCRIPTION
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 speci‐
fies 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 per‐
mitting 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 char‐
acter 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 exam‐
ple, 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 cre‐
ate a new record will cause the creation of multiple, empty records if
the record number is more than one greater than the largest record cur‐
rently in the database.
RESTRICTIONS
Only big and little endian byte order is supported.
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: 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)
Document Processing in a Relational Database System, Michael Stone‐
braker, Heidi Stettner, Joseph Kalash, Antonin Guttman, Nadene Lynn,
Memorandum No. UCB/ERL M82/32, May 1982.
recno(3)