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NAME    [Toc]    [Back]

     recno - record number database access method

SYNOPSIS    [Toc]    [Back]

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

DESCRIPTION    [Toc]    [Back]

     The dbopen() routine 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
     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() is
     defined in the <db.h> include file as follows:

     typedef struct {
           u_long flags;
           u_int cachesize;
           u_int psize;
           int lorder;
           size_t reclen;
           u_char bval;
           char *bfname;

     The elements of this structure are defined as follows:

     flags   The flag value is specified by  OR'ing  any  of  the
following values:

                     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(),  the
                     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
                     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() is called, instead of permitting any unmodified
 records to be read from  the  original

             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
             records.  If no value is  specified,  newlines  (`0)
are used to
             mark  the  end of variable-length records and fixedlength 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 file  name
for a dbopen
             of a btree file.

             The data part of the key/data pair used by the recno
             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 meta-data 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(),  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    [Toc]    [Back]

     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 fixedlength database
               that was too large to fit.

SEE ALSO    [Toc]    [Back]

     btree(3), dbopen(3), hash(3), mpool(3)

     Michael Stonebraker, Heidi Stettner, Joseph Kalash,  Antonin
Guttman, and
     Nadene  Lynn,  "Document Processing in a Relational Database
     Memorandum No. UCB/ERL M82/32, May 1982.

BUGS    [Toc]    [Back]

     Only big and little endian byte order is supported.

OpenBSD     3.6                         August      18,      1994
[ Back ]
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