xref: /dragonfly/lib/libc/db/man/recno.3 (revision 333227be) 
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32.\"	@(#)recno.3	8.5 (Berkeley) 8/18/94
33.\" $FreeBSD: src/lib/libc/db/man/recno.3,v 1.4.2.2 2001/12/14 18:33:49 ru Exp $
34.\" $DragonFly: src/lib/libc/db/man/recno.3,v 1.2 2003/06/17 04:26:41 dillon Exp $
35.\"
36.Dd August 18, 1994
37.Dt RECNO 3
38.Os
39.Sh NAME
40.Nm recno
41.Nd "record number database access method"
42.Sh SYNOPSIS
43.In sys/types.h
44.In db.h
45.Sh DESCRIPTION
46The routine
47.Fn dbopen
48is the library interface to database files.
49One of the supported file formats is record number files.
50The general description of the database access methods is in
51.Xr dbopen 3 ,
52this manual page describes only the
53.Nm
54specific information.
55.Pp
56The record number data structure is either variable or fixed-length
57records stored in a flat-file format, accessed by the logical record
58number.
59The existence of record number five implies the existence of records
60one through four, and the deletion of record number one causes
61record number five to be renumbered to record number four, as well
62as the cursor, if positioned after record number one, to shift down
63one record.
64.Pp
65The
66.Nm
67access method specific data structure provided to
68.Fn dbopen
69is defined in the
70.Aq Pa db.h
71include file as follows:
72.Bd -literal
73typedef struct {
74	u_long flags;
75	u_int cachesize;
76	u_int psize;
77	int lorder;
78	size_t reclen;
79	u_char bval;
80	char *bfname;
81} RECNOINFO;
82.Ed
83.Pp
84The elements of this structure are defined as follows:
85.Bl -tag -width indent
86.It Va flags
87The flag value is specified by
88.Em or Ns 'ing
89any of the following values:
90.Bl -tag -width indent
91.It Dv R_FIXEDLEN
92The records are fixed-length, not byte delimited.
93The structure element
94.Va reclen
95specifies the length of the record, and the structure element
96.Va bval
97is used as the pad character.
98Any records, inserted into the database, that are less than
99.Va reclen
100bytes long are automatically padded.
101.It Dv R_NOKEY
102In the interface specified by
103.Fn dbopen ,
104the sequential record retrieval fills in both the caller's key and
105data structures.
106If the
107.Dv R_NOKEY
108flag is specified, the
109.Em cursor
110routines are not required to fill in the key structure.
111This permits applications to retrieve records at the end of files without
112reading all of the intervening records.
113.It Dv R_SNAPSHOT
114This flag requires that a snapshot of the file be taken when
115.Fn dbopen
116is called, instead of permitting any unmodified records to be read from
117the original file.
118.El
119.It Va cachesize
120A suggested maximum size, in bytes, of the memory cache.
121This value is
122.Em only
123advisory, and the access method will allocate more memory rather than fail.
124If
125.Va cachesize
126is 0 (no size is specified) a default cache is used.
127.It Va psize
128The
129.Nm
130access method stores the in-memory copies of its records
131in a btree.
132This value is the size (in bytes) of the pages used for nodes in that tree.
133If
134.Va psize
135is 0 (no page size is specified) a page size is chosen based on the
136underlying file system I/O block size.
137See
138.Xr btree 3
139for more information.
140.It Va lorder
141The byte order for integers in the stored database metadata.
142The number should represent the order as an integer; for example,
143big endian order would be the number 4,321.
144If
145.Va lorder
146is 0 (no order is specified) the current host order is used.
147.It Va reclen
148The length of a fixed-length record.
149.It Va bval
150The delimiting byte to be used to mark the end of a record for
151variable-length records, and the pad character for fixed-length
152records.
153If no value is specified, newlines
154.Pq Dq \en
155are used to mark the end
156of variable-length records and fixed-length records are padded with
157spaces.
158.It Va bfname
159The
160.Nm
161access method stores the in-memory copies of its records
162in a btree.
163If
164.Va bfname
165is
166.No non\- Ns Dv NULL ,
167it specifies the name of the btree file,
168as if specified as the file name for a
169.Fn dbopen
170of a btree file.
171.El
172.Pp
173The data part of the key/data pair used by the
174.Nm
175access method
176is the same as other access methods.
177The key is different.
178The
179.Va data
180field of the key should be a pointer to a memory location of type
181.Ft recno_t ,
182as defined in the
183.Aq Pa db.h
184include file.
185This type is normally the largest unsigned integral type available to
186the implementation.
187The
188.Va size
189field of the key should be the size of that type.
190.Pp
191Because there can be no meta-data associated with the underlying
192.Nm
193access method files, any changes made to the default values
194(e.g. fixed record length or byte separator value) must be explicitly
195specified each time the file is opened.
196.Pp
197In the interface specified by
198.Fn dbopen ,
199using the
200.Va put
201interface to create a new record will cause the creation of multiple,
202empty records if the record number is more than one greater than the
203largest record currently in the database.
204.Sh ERRORS
205The
206.Nm
207access method routines may fail and set
208.Va errno
209for any of the errors specified for the library routine
210.Xr dbopen 3
211or the following:
212.Bl -tag -width Er
213.It Bq Er EINVAL
214An attempt was made to add a record to a fixed-length database that
215was too large to fit.
216.El
217.Sh SEE ALSO
218.Xr btree 3 ,
219.Xr dbopen 3 ,
220.Xr hash 3 ,
221.Xr mpool 3
222.Rs
223.%T "Document Processing in a Relational Database System"
224.%A Michael Stonebraker
225.%A Heidi Stettner
226.%A Joseph Kalash
227.%A Antonin Guttman
228.%A Nadene Lynn
229.%R "Memorandum No. UCB/ERL M82/32"
230.%D May 1982
231.Re
232.Sh BUGS
233Only big and little endian byte order is supported.
234