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recno(3)							      recno(3)

NAME
       recno - record number database access method

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

DESCRIPTION
       The routine dbopen() is the library interface to database files. One of
       the supported file formats is record number (recno) 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() 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: The flag value
       is specified by ORing any of the	 following  values:  The  records  are
       fixed  length,  not byte delimited. The structure element reclen speci‐
       fies 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  per‐
       mitting	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.   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.  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.
       The length of a fixed-length record.  The delimiting byte to be used to
       mark the end of a record for variable-length records and the pad	 char‐
       acter  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.  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 metadata associated with the underlying recno
       access method files, any changes made to the default values (for	 exam‐
       ple,  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 cre‐
       ate  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.

RESTRICTIONS
       Only big and little endian byte order is supported.

ERRORS
       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
       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.

								      recno(3)
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