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 .in +0.5i
  70 .nf
  71 typedef struct {
  72     u_long  flags;
  73     u_int   cachesize;
  74     u_int   psize;
  75     int     lorder;
  76     size_t  reclen;
  77     u_char  bval;
  78     char   *bfname;
  79 } RECNOINFO;
  80 .fi
  81 .in
  82 .PP
  83 The elements of this structure are defined as follows:
  84 .TP
  85 flags
  86 The flag value is specified by
  87 .IR or 'ing
  88 any of the following values:
  89 .RS
  90 .TP
  91 .B R_FIXEDLEN
  92 The records are fixed-length, not byte delimited.
  93 The structure element
  94 .I reclen
  95 specifies the length of the record, and the structure element
  96 .I bval
  97 is used as the pad character.
  98 Any records, inserted into the database, that are less than
  99 .I reclen
 100 bytes long are automatically padded.
 101 .TP
 102 .B R_NOKEY
 103 In the interface specified by
 104 .IR dbopen ,
 105 the sequential record retrieval fills in both the caller's key and
 106 data structures.
 107 If the
 108 .B R_NOKEY
 109 flag is specified, the
 110 .I cursor
 111 routines are not required to fill in the key structure.
 112 This permits applications to retrieve records at the end of files without
 113 reading all of the intervening records.
 114 .TP
 115 .B R_SNAPSHOT
 116 This flag requires that a snapshot of the file be taken when
 117 .I dbopen
 118 is called, instead of permitting any unmodified records to be read from
 119 the original file.
 120 .RE
 121 .TP
 122 .I cachesize
 123 A suggested maximum size, in bytes, of the memory cache.
 124 This value is
 125 .B only
 126 advisory, and the access method will allocate more memory rather than fail.
 127 If
 128 .I cachesize
 129 is  0 (no size is specified) a default cache is used.
 130 .TP
 131 .I psize
 132 The recno access method stores the in-memory copies of its records
 133 in a btree.
 134 This value is the size (in bytes) of the pages used for nodes in that tree.
 135 If
 136 .I psize
 137 is 0 (no page size is specified) a page size is chosen based on the
 138 underlying file system I/O block size.
 139 See
 140 .BR btree (3)
 141 for more information.
 142 .TP
 143 .I lorder
 144 The byte order for integers in the stored database metadata.
 145 The number should represent the order as an integer; for example,
 146 big endian order would be the number 4,321.
 147 If
 148 .I lorder
 149 is 0 (no order is specified) the current host order is used.
 150 .TP
 151 .I reclen
 152 The length of a fixed-length record.
 153 .TP
 154 .I bval
 155 The delimiting byte to be used to mark the end of a record for
 156 variable-length records, and the pad character for fixed-length
 157 records.
 158 If no value is specified, newlines ("\en") are used to mark the end
 159 of variable-length records and fixed-length records are padded with
 160 spaces.
 161 .TP
 162 .I bfname
 163 The recno access method stores the in-memory copies of its records
 164 in a btree.
 165 If
 166 .I bfname
 167 is non-NULL, it specifies the name of the btree file,
 168 as if specified as the filename for a dbopen of a btree file.
 169 .PP
 170 The data part of the key/data pair used by the
 171 .I recno
 172 access method
 173 is the same as other access methods.
 174 The key is different.
 175 The
 176 .I data
 177 field of the key should be a pointer to a memory location of type
 178 .IR recno_t ,
 179 as defined in th
 180 .I <db.h>
 181 include file.
 182 This type is normally the largest unsigned integral type available to
 183 the implementation.
 184 The
 185 .I size
 186 field of the key should be the size of that type.
 187 .PP
 188 Because there can be no metadata associated with the underlying
 189 recno access method files, any changes made to the default values
 190 (e.g., fixed record length or byte separator value) must be explicitly
 191 specified each time the file is opened.
 192 .PP
 193 In the interface specified by
 194 .IR dbopen ,
 195 using the
 196 .I put
 197 interface to create a new record will cause the creation of multiple,
 198 empty records if the record number is more than one greater than the
 199 largest record currently in the database.
 200 .SH ERRORS
 201 The
 202 .I recno
 203 access method routines may fail and set
 204 .I errno
 205 for any of the errors specified for the library routine
 206 .BR dbopen (3)
 207 or the following:
 208 .TP
 209 .B EINVAL
 210 An attempt was made to add a record to a fixed-length database that
 211 was too large to fit.
 212 .SH BUGS
 213 Only big and little endian byte order is supported.
 214 .SH "SEE ALSO"
 215 .BR btree (3)
 216 .BR dbopen (3),
 217 .BR hash (3),
 218 .BR mpool (3)
 219 .sp
 220 .IR "Document Processing in a Relational Database System" ,
 221 Michael Stonebraker, Heidi Stettner, Joseph Kalash, Antonin Guttman,
 222 Nadene Lynn, Memorandum No. UCB/ERL M82/32, May 1982.