4.4BSD/usr/share/man/cat3/recno.0
RECNO(3) BSD Programmer's Manual RECNO(3)
NNAAMMEE
recno - record number database access method
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DDEESSCCRRIIPPTTIIOONN
The routine _d_b_o_p_e_n 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 _d_b_o_p_e_n(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 _d_b_o_p_e_n is defined in the <db.h> include file as fol-
lows:
typedef struct {
u_long flags;
u_int cachesize;
int psize;
int lorder;
size_t reclen;
u_char bval;
char *bfname;
} RECNOINFO;
The elements of this structure are defined as follows:
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.
cachesize
A suggested maximum size, in bytes, of the memory
cache. This value is oonnllyy advisory, and the access
method will allocate more memory rather than fail.
If _c_a_c_h_e_s_i_z_e is 0 (no size is specified) a default
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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 _p_s_i_z_e is 0 (no page size is specified) a
page size is chosen based on the underlying file
system I/O block size. See _b_t_r_e_e(3) for more
information.
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 file name for a dbopen of a btree
file.
flags The flag value is specified by _o_r'ing any of the
following values:
R_FIXEDLEN
The records are fixed-length, not byte
delimited. The structure element _r_e_c_l_e_n
specifies the length of the record, and the
structure element _b_v_a_l is used as the pad
character.
R_NOKEY
In the interface specified by _d_b_o_p_e_n, the
sequential record retrieval fills in both
the caller's key and data structures. If
the R_NOKEY flag is specified, the _c_u_r_s_o_r
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 _d_b_o_p_e_n is called, instead
of permitting any unmodified records to be
read from the original file.
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 _l_o_r_d_e_r is 0 (no order is
specified) the current host order is used.
reclen The length of a fixed-length record.
The data part of the key/data pair used by the recno
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access method is the same as other access methods. The
key is different. The _d_a_t_a field of the key should be a
pointer to a memory location of type _r_e_c_n_o___t, as defined
in the <db.h> include file. This type is normally the
largest unsigned integral type available to the implemen-
tation. The _s_i_z_e field of the key should be the size of
that type.
In the interface specified by _d_b_o_p_e_n, using the _p_u_t inter-
face 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.
SSEEEE AALLSSOO
_d_b_o_p_e_n(3), _h_a_s_h(3), _m_p_o_o_l(3), _r_e_c_n_o(3)
_D_o_c_u_m_e_n_t _P_r_o_c_e_s_s_i_n_g _i_n _a _R_e_l_a_t_i_o_n_a_l _D_a_t_a_b_a_s_e _S_y_s_t_e_m,
Michael Stonebraker, Heidi Stettner, Joseph Kalash,
Antonin Guttman, Nadene Lynn, Memorandum No. UCB/ERL
M82/32, May 1982.
BBUUGGSS
Only big and little endian byte order is supported.
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