Manpage of RECNO

RECNO

Section: Linux Programmer's Manual (3)
Updated: 2012-04-23
Index
 

NAME

recno - record number database access method  

SYNOPSIS

#include <sys/types.h>
#include <db.h>
 

DESCRIPTION

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 libdblibrary 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 reclenspecifies the length of the record, and the structure element bvalis used as the pad character. Any records, inserted into the database, that are less than reclenbytes 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_NOKEYflag is specified, the cursorroutines 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 onlyadvisory, and the access method will allocate more memory rather than fail. If cachesizeis 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 psizeis 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 lorderis 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 bfnameis 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 recnoaccess method is the same as other access methods. The key is different. The datafield 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 sizefield 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 putinterface 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.  

ERRORS

The recnoaccess method routines may fail and set errnofor 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.
 

BUGS

Only big and little endian byte order is supported.  

SEE ALSO

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.


 

Index

NAME
SYNOPSIS
DESCRIPTION
ERRORS
BUGS
SEE ALSO

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Time: 22:27:46 GMT, June 20, 2016