Skip site navigation (1)Skip section navigation (2)

FreeBSD Manual Pages


home | help
RECNO(3)		   Library Functions Manual		      RECNO(3)

       recno - record number database access method

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

       The  routine dbopen is the library interface to database	files.	One of
       the supported file formats is record number  files.   The  general  de-
       scription  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

       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;
       } RECNOINFO;

       The elements of this structure are defined as follows:

       flags  The  flag	value is specified by or'ing 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	database, that
		     are less than reclen bytes	long are automatically padded.

		     In	the interface  specified  by  dbopen,  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 is called, instead of permitting any  unmodi-
		     fied 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	speci-
	      fied) 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 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 file name for a
	      dbopen 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	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  cur-
       rently in the database.

       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:

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

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

       Document	 Processing  in	 a  Relational Database	System,	Michael	Stone-
       braker, Heidi Stettner, Joseph Kalash, Antonin  Guttman,	 Nadene	 Lynn,
       Memorandum No. UCB/ERL M82/32, May 1982.

       Only big	and little endian byte order is	supported.

4.4 Berkeley Distribution	  1994-08-18			      RECNO(3)


Want to link to this manual page? Use this URL:

home | help