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:
flagsThe flag value is specified by ORing any of the following values:
R_FIXEDLENThe records are fixed-length, not byte delimited. The structure element
reclenspecifies the length of the record, and the structure elementbvalis used as the pad character. Any records, inserted into the database, that are less thanreclenbytes long are automatically padded.R_NOKEYIn the interface specified by dbopen(3), the sequential record retrieval fills in both the caller's key and data structures. If the
R_NOKEYflag 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_SNAPSHOTThis 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.
cachesizeA 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.
psizeThe 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.
lorderThe 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.
reclenThe length of a fixed-length record.
bvalThe 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.
bfnameThe 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:
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.
This page is part of release 3.35 of the Linux man-pages project. A
description of the project, and information about reporting
bugs, can be found at http://man7.org/linux/man-pages/.
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