man3/recno.3

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  32 .\"     @(#)recno.3     8.5 (Berkeley) 8/18/94
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  34 .TH RECNO 3 1994-08-18 "" "Linux Programmer's Manual"
  35 .UC 7
  36 .SH NAME
  37 recno \- record number database access method
  38 .SH SYNOPSIS
  39 .nf
  40 .ft B
  41 #include <sys/types.h>
  42 #include <db.h>
  43 .ft R
  44 .fi
  45 .SH DESCRIPTION
  46 The routine
  47 .I dbopen
  48 is the library interface to database files.
  49 One of the supported file formats is record number files.
  50 The general description of the database access methods is in
  51 .BR dbopen (3),
  52 this manual page describes only the recno specific information.
  53 .PP
  54 The record number data structure is either variable or fixed-length
  55 records stored in a flat-file format, accessed by the logical record
  56 number.
  57 The existence of record number five implies the existence of records
  58 one through four, and the deletion of record number one causes
  59 record number five to be renumbered to record number four, as well
  60 as the cursor, if positioned after record number one, to shift down
  61 one record.
  62 .PP
  63 The recno access method specific data structure provided to
  64 .I dbopen
  65 is defined in the
  66 .I <db.h>
  67 include file as follows:
  68 .PP
  69 .nf
  70 typedef struct {
  71     u_long  flags;
  72     u_int   cachesize;
  73     u_int   psize;
  74     int     lorder;
  75     size_t  reclen;
  76     u_char  bval;
  77     char   *bfname;
  78 } RECNOINFO;
  79 .fi
  80 .PP
  81 The elements of this structure are defined as follows:
  82 .TP
  83 flags
  84 The flag value is specified by
  85 .IR or 'ing
  86 any of the following values:
  87 .RS
  88 .TP
  89 .B R_FIXEDLEN
  90 The records are fixed-length, not byte delimited.
  91 The structure element
  92 .I reclen
  93 specifies the length of the record, and the structure element
  94 .I bval
  95 is used as the pad character.
  96 Any records, inserted into the database, that are less than
  97 .I reclen
  98 bytes long are automatically padded.
  99 .TP
 100 .B R_NOKEY
 101 In the interface specified by
 102 .IR dbopen ,
 103 the sequential record retrieval fills in both the caller's key and
 104 data structures.
 105 If the
 106 .B R_NOKEY
 107 flag is specified, the
 108 .I cursor
 109 routines are not required to fill in the key structure.
 110 This permits applications to retrieve records at the end of files without
 111 reading all of the intervening records.
 112 .TP
 113 .B R_SNAPSHOT
 114 This flag requires that a snapshot of the file be taken when
 115 .I dbopen
 116 is called, instead of permitting any unmodified records to be read from
 117 the original file.
 118 .RE
 119 .TP
 120 cachesize
 121 A suggested maximum size, in bytes, of the memory cache.
 122 This value is
 123 .B only
 124 advisory, and the access method will allocate more memory rather than fail.
 125 If
 126 .I cachesize
 127 is  0 (no size is specified) a default cache is used.
 128 .TP
 129 psize
 130 The recno access method stores the in-memory copies of its records
 131 in a btree.
 132 This value is the size (in bytes) of the pages used for nodes in that tree.
 133 If
 134 .I psize
 135 is 0 (no page size is specified) a page size is chosen based on the
 136 underlying file system I/O block size.
 137 See
 138 .BR btree (3)
 139 for more information.
 140 .TP
 141 lorder
 142 The byte order for integers in the stored database metadata.
 143 The number should represent the order as an integer; for example,
 144 big endian order would be the number 4,321.
 145 If
 146 .I lorder
 147 is 0 (no order is specified) the current host order is used.
 148 .TP
 149 reclen
 150 The length of a fixed-length record.
 151 .TP
 152 bval
 153 The delimiting byte to be used to mark the end of a record for
 154 variable-length records, and the pad character for fixed-length
 155 records.
 156 If no value is specified, newlines (``\en'') are used to mark the end
 157 of variable-length records and fixed-length records are padded with
 158 spaces.
 159 .TP
 160 bfname
 161 The recno access method stores the in-memory copies of its records
 162 in a btree.
 163 If bfname is non-NULL, it specifies the name of the btree file,
 164 as if specified as the filename for a dbopen of a btree file.
 165 .PP
 166 The data part of the key/data pair used by the recno access method
 167 is the same as other access methods.
 168 The key is different.
 169 The
 170 .I data
 171 field of the key should be a pointer to a memory location of type
 172 .IR recno_t ,
 173 as defined in th
 174 .I <db.h
 175 include file.
 176 This type is normally the largest unsigned integral type available to
 177 the implementation.
 178 The
 179 .I size
 180 field of the key should be the size of that type.
 181 .PP
 182 Because there can be no metadata associated with the underlying
 183 recno access method files, any changes made to the default values
 184 (e.g., fixed record length or byte separator value) must be explicitly
 185 specified each time the file is opened.
 186 .PP
 187 In the interface specified by
 188 .IR dbopen ,
 189 using the
 190 .I put
 191 interface to create a new record will cause the creation of multiple,
 192 empty records if the record number is more than one greater than the
 193 largest record currently in the database.
 194 .SH ERRORS
 195 The
 196 .I recno
 197 access method routines may fail and set
 198 .I errno
 199 for any of the errors specified for the library routine
 200 .BR dbopen (3)
 201 or the following:
 202 .TP
 203 .B EINVAL
 204 An attempt was made to add a record to a fixed-length database that
 205 was too large to fit.
 206 .SH BUGS
 207 Only big and little endian byte order is supported.
 208 .SH "SEE ALSO"
 209 .BR btree (3)
 210 .BR dbopen (3),
 211 .BR hash (3),
 212 .BR mpool (3)
 213 .sp
 214 .IR "Document Processing in a Relational Database System" ,
 215 Michael Stonebraker, Heidi Stettner, Joseph Kalash, Antonin Guttman,
 216 Nadene Lynn, Memorandum No. UCB/ERL M82/32, May 1982.