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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  routine dbopen 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

       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 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 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  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 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 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  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 following:

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

SEE ALSO    [Toc]    [Back]

       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.

BUGS    [Toc]    [Back]

       Only big and little endian byte order is supported.

4.4 Berkeley Distribution	  1994-08-18			      RECNO(3)
[ Back ]
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