NAME
recno - record number database access method
SYNOPSIS
#include <sys/types.h> #include <db.h>
DESCRIPTION
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:
| ||||||||||||
cachesize | |||||||||||||
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. | |||||||||||||
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 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. | ||||||||||||
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 lorder is 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 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. | ||||||||||||
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.
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:
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.
COLOPHON
This page is part of release 3.23 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.