db/man/FreeBSD/recno.3

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  28 .\"     @(#)recno.3     8.5 (Berkeley) 8/18/94
  29 .\" $FreeBSD: src/lib/libc/db/man/recno.3,v 1.9 2007/01/09 00:27:51 imp Exp $
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  31 .Dd August 18, 1994
  32 .Dt RECNO 3
  33 .Os
  34 .Sh NAME
  35 .Nm recno
  36 .Nd "record number database access method"
  37 .Sh SYNOPSIS
  38 .In sys/types.h
  39 .In db.h
  40 .Sh DESCRIPTION
  41 The routine
  42 .Fn dbopen
  43 is the library interface to database files.
  44 One of the supported file formats is record number files.
  45 The general description of the database access methods is in
  46 .Xr dbopen 3 ,
  47 this manual page describes only the
  48 .Nm
  49 specific information.
  50 .Pp
  51 The record number data structure is either variable or fixed-length
  52 records stored in a flat-file format, accessed by the logical record
  53 number.
  54 The existence of record number five implies the existence of records
  55 one through four, and the deletion of record number one causes
  56 record number five to be renumbered to record number four, as well
  57 as the cursor, if positioned after record number one, to shift down
  58 one record.
  59 .Pp
  60 The
  61 .Nm
  62 access method specific data structure provided to
  63 .Fn dbopen
  64 is defined in the
  65 .In db.h
  66 include file as follows:
  67 .Bd -literal
  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 .Ed
  78 .Pp
  79 The elements of this structure are defined as follows:
  80 .Bl -tag -width indent
  81 .It Va flags
  82 The flag value is specified by
  83 .Em or Ns 'ing
  84 any of the following values:
  85 .Bl -tag -width indent
  86 .It Dv R_FIXEDLEN
  87 The records are fixed-length, not byte delimited.
  88 The structure element
  89 .Va reclen
  90 specifies the length of the record, and the structure element
  91 .Va bval
  92 is used as the pad character.
  93 Any records, inserted into the database, that are less than
  94 .Va reclen
  95 bytes long are automatically padded.
  96 .It Dv R_NOKEY
  97 In the interface specified by
  98 .Fn dbopen ,
  99 the sequential record retrieval fills in both the caller's key and
 100 data structures.
 101 If the
 102 .Dv R_NOKEY
 103 flag is specified, the
 104 .Em 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 .It Dv R_SNAPSHOT
 109 This flag requires that a snapshot of the file be taken when
 110 .Fn dbopen
 111 is called, instead of permitting any unmodified records to be read from
 112 the original file.
 113 .El
 114 .It Va cachesize
 115 A suggested maximum size, in bytes, of the memory cache.
 116 This value is
 117 .Em only
 118 advisory, and the access method will allocate more memory rather than fail.
 119 If
 120 .Va cachesize
 121 is 0 (no size is specified) a default cache is used.
 122 .It Va psize
 123 The
 124 .Nm
 125 access method stores the in-memory copies of its records
 126 in a btree.
 127 This value is the size (in bytes) of the pages used for nodes in that tree.
 128 If
 129 .Va psize
 130 is 0 (no page size is specified) a page size is chosen based on the
 131 underlying file system I/O block size.
 132 See
 133 .Xr btree 3
 134 for more information.
 135 .It Va lorder
 136 The byte order for integers in the stored database metadata.
 137 The number should represent the order as an integer; for example,
 138 big endian order would be the number 4,321.
 139 If
 140 .Va lorder
 141 is 0 (no order is specified) the current host order is used.
 142 .It Va reclen
 143 The length of a fixed-length record.
 144 .It Va bval
 145 The delimiting byte to be used to mark the end of a record for
 146 variable-length records, and the pad character for fixed-length
 147 records.
 148 If no value is specified, newlines
 149 .Pq Dq \en
 150 are used to mark the end
 151 of variable-length records and fixed-length records are padded with
 152 spaces.
 153 .It Va bfname
 154 The
 155 .Nm
 156 access method stores the in-memory copies of its records
 157 in a btree.
 158 If
 159 .Va bfname
 160 is
 161 .No non\- Ns Dv NULL ,
 162 it specifies the name of the btree file,
 163 as if specified as the file name for a
 164 .Fn dbopen
 165 of a btree file.
 166 .El
 167 .Pp
 168 The data part of the key/data pair used by the
 169 .Nm
 170 access method
 171 is the same as other access methods.
 172 The key is different.
 173 The
 174 .Va data
 175 field of the key should be a pointer to a memory location of type
 176 .Ft recno_t ,
 177 as defined in the
 178 .In db.h
 179 include file.
 180 This type is normally the largest unsigned integral type available to
 181 the implementation.
 182 The
 183 .Va size
 184 field of the key should be the size of that type.
 185 .Pp
 186 Because there can be no meta-data associated with the underlying
 187 .Nm
 188 access method files, any changes made to the default values
 189 (e.g.\& fixed record length or byte separator value) must be explicitly
 190 specified each time the file is opened.
 191 .Pp
 192 In the interface specified by
 193 .Fn dbopen ,
 194 using the
 195 .Va put
 196 interface to create a new record will cause the creation of multiple,
 197 empty records if the record number is more than one greater than the
 198 largest record currently in the database.
 199 .Sh ERRORS
 200 The
 201 .Nm
 202 access method routines may fail and set
 203 .Va errno
 204 for any of the errors specified for the library routine
 205 .Xr dbopen 3
 206 or the following:
 207 .Bl -tag -width Er
 208 .It Bq Er EINVAL
 209 An attempt was made to add a record to a fixed-length database that
 210 was too large to fit.
 211 .El
 212 .Sh SEE ALSO
 213 .Xr btree 3 ,
 214 .Xr dbopen 3 ,
 215 .Xr hash 3 ,
 216 .Xr mpool 3
 217 .Rs
 218 .%T "Document Processing in a Relational Database System"
 219 .%A Michael Stonebraker
 220 .%A Heidi Stettner
 221 .%A Joseph Kalash
 222 .%A Antonin Guttman
 223 .%A Nadene Lynn
 224 .%R "Memorandum No. UCB/ERL M82/32"
 225 .%D May 1982
 226 .Re
 227 .Sh BUGS
 228 Only big and little endian byte order is supported.