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