recno(3) — Linux manual page


recno(3)                Library Functions Manual                recno(3)

NAME         top

       recno - record number database access method

LIBRARY         top

       Standard C library (libc, -lc)

SYNOPSIS         top

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

DESCRIPTION         top

       Note well: This page documents interfaces provided up until glibc
       2.1.  Since glibc 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

       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

                     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 database, that are less than reclen bytes
                     long are automatically 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

                     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 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 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 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.

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

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4.4 Berkeley Distribution      2024-06-15                       recno(3)

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