db/man/FreeBSD/recno.3

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  32 .\"     @(#)recno.3     8.5 (Berkeley) 8/18/94
  33 .\" $FreeBSD: src/lib/libc/db/man/recno.3,v 1.8 2004/07/02 23:52:10 ru Exp $
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  35 .Dd August 18, 1994
  36 .Dt RECNO 3
  37 .Os
  38 .Sh NAME
  39 .Nm recno
  40 .Nd "record number database access method"
  41 .Sh SYNOPSIS
  42 .In sys/types.h
  43 .In db.h
  44 .Sh DESCRIPTION
  45 The routine
  46 .Fn dbopen
  47 is the library interface to database files.
  48 One of the supported file formats is record number files.
  49 The general description of the database access methods is in
  50 .Xr dbopen 3 ,
  51 this manual page describes only the
  52 .Nm
  53 specific information.
  54 .Pp
  55 The record number data structure is either variable or fixed-length
  56 records stored in a flat-file format, accessed by the logical record
  57 number.
  58 The existence of record number five implies the existence of records
  59 one through four, and the deletion of record number one causes
  60 record number five to be renumbered to record number four, as well
  61 as the cursor, if positioned after record number one, to shift down
  62 one record.
  63 .Pp
  64 The
  65 .Nm
  66 access method specific data structure provided to
  67 .Fn dbopen
  68 is defined in the
  69 .In db.h
  70 include file as follows:
  71 .Bd -literal
  72 typedef struct {
  73         u_long flags;
  74         u_int cachesize;
  75         u_int psize;
  76         int lorder;
  77         size_t reclen;
  78         u_char bval;
  79         char *bfname;
  80 } RECNOINFO;
  81 .Ed
  82 .Pp
  83 The elements of this structure are defined as follows:
  84 .Bl -tag -width indent
  85 .It Va flags
  86 The flag value is specified by
  87 .Em or Ns 'ing
  88 any of the following values:
  89 .Bl -tag -width indent
  90 .It Dv R_FIXEDLEN
  91 The records are fixed-length, not byte delimited.
  92 The structure element
  93 .Va reclen
  94 specifies the length of the record, and the structure element
  95 .Va bval
  96 is used as the pad character.
  97 Any records, inserted into the database, that are less than
  98 .Va reclen
  99 bytes long are automatically padded.
 100 .It Dv R_NOKEY
 101 In the interface specified by
 102 .Fn dbopen ,
 103 the sequential record retrieval fills in both the caller's key and
 104 data structures.
 105 If the
 106 .Dv R_NOKEY
 107 flag is specified, the
 108 .Em 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 .It Dv R_SNAPSHOT
 113 This flag requires that a snapshot of the file be taken when
 114 .Fn dbopen
 115 is called, instead of permitting any unmodified records to be read from
 116 the original file.
 117 .El
 118 .It Va cachesize
 119 A suggested maximum size, in bytes, of the memory cache.
 120 This value is
 121 .Em only
 122 advisory, and the access method will allocate more memory rather than fail.
 123 If
 124 .Va cachesize
 125 is 0 (no size is specified) a default cache is used.
 126 .It Va psize
 127 The
 128 .Nm
 129 access method stores the in-memory copies of its records
 130 in a btree.
 131 This value is the size (in bytes) of the pages used for nodes in that tree.
 132 If
 133 .Va psize
 134 is 0 (no page size is specified) a page size is chosen based on the
 135 underlying file system I/O block size.
 136 See
 137 .Xr btree 3
 138 for more information.
 139 .It Va lorder
 140 The byte order for integers in the stored database metadata.
 141 The number should represent the order as an integer; for example,
 142 big endian order would be the number 4,321.
 143 If
 144 .Va lorder
 145 is 0 (no order is specified) the current host order is used.
 146 .It Va reclen
 147 The length of a fixed-length record.
 148 .It Va 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
 153 .Pq Dq \en
 154 are used to mark the end
 155 of variable-length records and fixed-length records are padded with
 156 spaces.
 157 .It Va bfname
 158 The
 159 .Nm
 160 access method stores the in-memory copies of its records
 161 in a btree.
 162 If
 163 .Va bfname
 164 is
 165 .No non\- Ns Dv NULL ,
 166 it specifies the name of the btree file,
 167 as if specified as the file name for a
 168 .Fn dbopen
 169 of a btree file.
 170 .El
 171 .Pp
 172 The data part of the key/data pair used by the
 173 .Nm
 174 access method
 175 is the same as other access methods.
 176 The key is different.
 177 The
 178 .Va data
 179 field of the key should be a pointer to a memory location of type
 180 .Ft recno_t ,
 181 as defined in the
 182 .In db.h
 183 include file.
 184 This type is normally the largest unsigned integral type available to
 185 the implementation.
 186 The
 187 .Va size
 188 field of the key should be the size of that type.
 189 .Pp
 190 Because there can be no meta-data associated with the underlying
 191 .Nm
 192 access method files, any changes made to the default values
 193 (e.g.\& fixed record length or byte separator value) must be explicitly
 194 specified each time the file is opened.
 195 .Pp
 196 In the interface specified by
 197 .Fn dbopen ,
 198 using the
 199 .Va put
 200 interface to create a new record will cause the creation of multiple,
 201 empty records if the record number is more than one greater than the
 202 largest record currently in the database.
 203 .Sh ERRORS
 204 The
 205 .Nm
 206 access method routines may fail and set
 207 .Va errno
 208 for any of the errors specified for the library routine
 209 .Xr dbopen 3
 210 or the following:
 211 .Bl -tag -width Er
 212 .It Bq Er EINVAL
 213 An attempt was made to add a record to a fixed-length database that
 214 was too large to fit.
 215 .El
 216 .Sh SEE ALSO
 217 .Xr btree 3 ,
 218 .Xr dbopen 3 ,
 219 .Xr hash 3 ,
 220 .Xr mpool 3
 221 .Rs
 222 .%T "Document Processing in a Relational Database System"
 223 .%A Michael Stonebraker
 224 .%A Heidi Stettner
 225 .%A Joseph Kalash
 226 .%A Antonin Guttman
 227 .%A Nadene Lynn
 228 .%R "Memorandum No. UCB/ERL M82/32"
 229 .%D May 1982
 230 .Re
 231 .Sh BUGS
 232 Only big and little endian byte order is supported.