recno(3) — Linux manual page


RECNO(3)                  Linux Programmer's Manual                 RECNO(3)

NAME         top

       recno - record number database access method

SYNOPSIS         top

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

DESCRIPTION         top

       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
       libdb library 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 val‐

                     The records are fixed-length, not byte delimited.  The
                     structure element reclen specifies the length of the
                     record, and the structure element bval is used as the
                     pad character.  Any records, inserted into the data‐
                     base, that are less than reclen bytes long are automat‐
                     ically padded.

                     In the interface specified by dbopen(3), 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(3) is called, instead of permitting 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.

       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 under‐
              lying filesystem I/O block size.  See btree(3) for more infor‐

       lorder The byte order for integers in the stored database metadata.
              The number should represent the order as an integer; for exam‐
              ple, 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.

       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 nor‐
       mally the largest unsigned integral type available to the implementa‐
       tion.  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 spec‐
       ified 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         top

       The recno access method routines may fail and set errno for any of
       the errors specified for the library routine dbopen(3) or the

       EINVAL An attempt was made to add a record to a fixed-length database
              that was too large to fit.

BUGS         top

       Only big and little endian byte order is supported.

SEE ALSO         top

       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         top

       This page is part of release 5.08 of the Linux man-pages project.  A
       description of the project, information about reporting bugs, and the
       latest version of this page, can be found at

4.4 Berkeley Distribution        2017-09-15                         RECNO(3)

Pages that refer to this page: btree(3)db(3)dbopen(3)hash(3)mpool(3)