man3/recno.3

   1 .\" Copyright (c) 1990, 1993
   2 .\"     The Regents of the University of California.  All rights reserved.
   3 .\"
   4 .\" SPDX-License-Identifier: BSD-4-Clause-UC
   5 .\"
   6 .\"     @(#)recno.3     8.5 (Berkeley) 8/18/94
   7 .\"
   8 .TH RECNO 3 2017-09-15 "Linux man-pages (unreleased)" "Linux Programmer's Manual"
   9 .UC 7
  10 .SH NAME
  11 recno \- record number database access method
  12 .SH LIBRARY
  13 Standard C library
  14 .RI ( libc ", " \-lc )
  15 .SH SYNOPSIS
  16 .nf
  17 .ft B
  18 #include <sys/types.h>
  19 #include <db.h>
  20 .ft R
  21 .fi
  22 .SH DESCRIPTION
  23 .IR "Note well" :
  24 This page documents interfaces provided in glibc up until version 2.1.
  25 Since version 2.2, glibc no longer provides these interfaces.
  26 Probably, you are looking for the APIs provided by the
  27 .I libdb
  28 library instead.
  29 .PP
  30 The routine
  31 .BR dbopen (3)
  32 is the library interface to database files.
  33 One of the supported file formats is record number files.
  34 The general description of the database access methods is in
  35 .BR dbopen (3),
  36 this manual page describes only the recno-specific information.
  37 .PP
  38 The record number data structure is either variable or fixed-length
  39 records stored in a flat-file format, accessed by the logical record
  40 number.
  41 The existence of record number five implies the existence of records
  42 one through four, and the deletion of record number one causes
  43 record number five to be renumbered to record number four, as well
  44 as the cursor, if positioned after record number one, to shift down
  45 one record.
  46 .PP
  47 The recno access-method-specific data structure provided to
  48 .BR dbopen (3)
  49 is defined in the
  50 .I <db.h>
  51 include file as follows:
  52 .PP
  53 .in +4n
  54 .EX
  55 typedef struct {
  56     unsigned long flags;
  57     unsigned int  cachesize;
  58     unsigned int  psize;
  59     int           lorder;
  60     size_t        reclen;
  61     unsigned char bval;
  62     char         *bfname;
  63 } RECNOINFO;
  64 .EE
  65 .in
  66 .PP
  67 The elements of this structure are defined as follows:
  68 .TP
  69 .I flags
  70 The flag value is specified by ORing
  71 any of the following values:
  72 .RS
  73 .TP
  74 .B R_FIXEDLEN
  75 The records are fixed-length, not byte delimited.
  76 The structure element
  77 .I reclen
  78 specifies the length of the record, and the structure element
  79 .I bval
  80 is used as the pad character.
  81 Any records, inserted into the database, that are less than
  82 .I reclen
  83 bytes long are automatically padded.
  84 .TP
  85 .B R_NOKEY
  86 In the interface specified by
  87 .BR dbopen (3),
  88 the sequential record retrieval fills in both the caller's key and
  89 data structures.
  90 If the
  91 .B R_NOKEY
  92 flag is specified, the
  93 .I cursor
  94 routines are not required to fill in the key structure.
  95 This permits applications to retrieve records at the end of files without
  96 reading all of the intervening records.
  97 .TP
  98 .B R_SNAPSHOT
  99 This flag requires that a snapshot of the file be taken when
 100 .BR dbopen (3)
 101 is called, instead of permitting any unmodified records to be read from
 102 the original file.
 103 .RE
 104 .TP
 105 .I cachesize
 106 A suggested maximum size, in bytes, of the memory cache.
 107 This value is
 108 .B only
 109 advisory, and the access method will allocate more memory rather than fail.
 110 If
 111 .I cachesize
 112 is  0 (no size is specified), a default cache is used.
 113 .TP
 114 .I psize
 115 The recno access method stores the in-memory copies of its records
 116 in a btree.
 117 This value is the size (in bytes) of the pages used for nodes in that tree.
 118 If
 119 .I psize
 120 is 0 (no page size is specified), a page size is chosen based on the
 121 underlying filesystem I/O block size.
 122 See
 123 .BR btree (3)
 124 for more information.
 125 .TP
 126 .I lorder
 127 The byte order for integers in the stored database metadata.
 128 The number should represent the order as an integer; for example,
 129 big endian order would be the number 4,321.
 130 If
 131 .I lorder
 132 is 0 (no order is specified), the current host order is used.
 133 .TP
 134 .I reclen
 135 The length of a fixed-length record.
 136 .TP
 137 .I bval
 138 The delimiting byte to be used to mark the end of a record for
 139 variable-length records, and the pad character for fixed-length
 140 records.
 141 If no value is specified, newlines ("\en") are used to mark the end
 142 of variable-length records and fixed-length records are padded with
 143 spaces.
 144 .TP
 145 .I bfname
 146 The recno access method stores the in-memory copies of its records
 147 in a btree.
 148 If
 149 .I bfname
 150 is non-NULL, it specifies the name of the btree file,
 151 as if specified as the filename for a
 152 .BR dbopen (3)
 153 of a btree file.
 154 .PP
 155 The data part of the key/data pair used by the
 156 .I recno
 157 access method
 158 is the same as other access methods.
 159 The key is different.
 160 The
 161 .I data
 162 field of the key should be a pointer to a memory location of type
 163 .IR recno_t ,
 164 as defined in the
 165 .I <db.h>
 166 include file.
 167 This type is normally the largest unsigned integral type available to
 168 the implementation.
 169 The
 170 .I size
 171 field of the key should be the size of that type.
 172 .PP
 173 Because there can be no metadata associated with the underlying
 174 recno access method files, any changes made to the default values
 175 (e.g., fixed record length or byte separator value) must be explicitly
 176 specified each time the file is opened.
 177 .PP
 178 In the interface specified by
 179 .BR dbopen (3),
 180 using the
 181 .I put
 182 interface to create a new record will cause the creation of multiple,
 183 empty records if the record number is more than one greater than the
 184 largest record currently in the database.
 185 .SH ERRORS
 186 The
 187 .I recno
 188 access method routines may fail and set
 189 .I errno
 190 for any of the errors specified for the library routine
 191 .BR dbopen (3)
 192 or the following:
 193 .TP
 194 .B EINVAL
 195 An attempt was made to add a record to a fixed-length database that
 196 was too large to fit.
 197 .SH BUGS
 198 Only big and little endian byte order is supported.
 199 .SH SEE ALSO
 200 .BR btree (3),
 201 .BR dbopen (3),
 202 .BR hash (3),
 203 .BR mpool (3)
 204 .PP
 205 .IR "Document Processing in a Relational Database System" ,
 206 Michael Stonebraker, Heidi Stettner, Joseph Kalash, Antonin Guttman,
 207 Nadene Lynn, Memorandum No. UCB/ERL M82/32, May 1982.