xref: /dragonfly/lib/libc/db/man/recno.3 (revision fcce2b94) 
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28.\"	@(#)recno.3	8.5 (Berkeley) 8/18/94
29.\" $FreeBSD: src/lib/libc/db/man/recno.3,v 1.4.2.2 2001/12/14 18:33:49 ru Exp $
30.\" $DragonFly: src/lib/libc/db/man/recno.3,v 1.4 2006/05/26 19:39:36 swildner Exp $
31.\"
32.Dd August 18, 1994
33.Dt RECNO 3
34.Os
35.Sh NAME
36.Nm recno
37.Nd "record number database access method"
38.Sh SYNOPSIS
39.In sys/types.h
40.In db.h
41.Sh DESCRIPTION
42The routine
43.Fn dbopen
44is the library interface to database files.
45One of the supported file formats is record number files.
46The general description of the database access methods is in
47.Xr dbopen 3 ,
48this manual page describes only the
49.Nm
50specific information.
51.Pp
52The record number data structure is either variable or fixed-length
53records stored in a flat-file format, accessed by the logical record
54number.
55The existence of record number five implies the existence of records
56one through four, and the deletion of record number one causes
57record number five to be renumbered to record number four, as well
58as the cursor, if positioned after record number one, to shift down
59one record.
60.Pp
61The
62.Nm
63access method specific data structure provided to
64.Fn dbopen
65is defined in the
66.In db.h
67include file as follows:
68.Bd -literal
69typedef struct {
70	u_long flags;
71	u_int cachesize;
72	u_int psize;
73	int lorder;
74	size_t reclen;
75	u_char bval;
76	char *bfname;
77} RECNOINFO;
78.Ed
79.Pp
80The elements of this structure are defined as follows:
81.Bl -tag -width indent
82.It Va flags
83The flag value is specified by
84.Em or Ns 'ing
85any of the following values:
86.Bl -tag -width indent
87.It Dv R_FIXEDLEN
88The records are fixed-length, not byte delimited.
89The structure element
90.Va reclen
91specifies the length of the record, and the structure element
92.Va bval
93is used as the pad character.
94Any records, inserted into the database, that are less than
95.Va reclen
96bytes long are automatically padded.
97.It Dv R_NOKEY
98In the interface specified by
99.Fn dbopen ,
100the sequential record retrieval fills in both the caller's key and
101data structures.
102If the
103.Dv R_NOKEY
104flag is specified, the
105.Em cursor
106routines are not required to fill in the key structure.
107This permits applications to retrieve records at the end of files without
108reading all of the intervening records.
109.It Dv R_SNAPSHOT
110This flag requires that a snapshot of the file be taken when
111.Fn dbopen
112is called, instead of permitting any unmodified records to be read from
113the original file.
114.El
115.It Va cachesize
116A suggested maximum size, in bytes, of the memory cache.
117This value is
118.Em only
119advisory, and the access method will allocate more memory rather than fail.
120If
121.Va cachesize
122is 0 (no size is specified) a default cache is used.
123.It Va psize
124The
125.Nm
126access method stores the in-memory copies of its records
127in a btree.
128This value is the size (in bytes) of the pages used for nodes in that tree.
129If
130.Va psize
131is 0 (no page size is specified) a page size is chosen based on the
132underlying file system I/O block size.
133See
134.Xr btree 3
135for more information.
136.It Va lorder
137The byte order for integers in the stored database metadata.
138The number should represent the order as an integer; for example,
139big endian order would be the number 4,321.
140If
141.Va lorder
142is 0 (no order is specified) the current host order is used.
143.It Va reclen
144The length of a fixed-length record.
145.It Va bval
146The delimiting byte to be used to mark the end of a record for
147variable-length records, and the pad character for fixed-length
148records.
149If no value is specified, newlines
150.Pq Dq \en
151are used to mark the end
152of variable-length records and fixed-length records are padded with
153spaces.
154.It Va bfname
155The
156.Nm
157access method stores the in-memory copies of its records
158in a btree.
159If
160.Va bfname
161is
162.No non\- Ns Dv NULL ,
163it specifies the name of the btree file,
164as if specified as the file name for a
165.Fn dbopen
166of a btree file.
167.El
168.Pp
169The data part of the key/data pair used by the
170.Nm
171access method
172is the same as other access methods.
173The key is different.
174The
175.Va data
176field of the key should be a pointer to a memory location of type
177.Ft recno_t ,
178as defined in the
179.In db.h
180include file.
181This type is normally the largest unsigned integral type available to
182the implementation.
183The
184.Va size
185field of the key should be the size of that type.
186.Pp
187Because there can be no meta-data associated with the underlying
188.Nm
189access method files, any changes made to the default values
190(e.g. fixed record length or byte separator value) must be explicitly
191specified each time the file is opened.
192.Pp
193In the interface specified by
194.Fn dbopen ,
195using the
196.Va put
197interface to create a new record will cause the creation of multiple,
198empty records if the record number is more than one greater than the
199largest record currently in the database.
200.Sh ERRORS
201The
202.Nm
203access method routines may fail and set
204.Va errno
205for any of the errors specified for the library routine
206.Xr dbopen 3
207or the following:
208.Bl -tag -width Er
209.It Bq Er EINVAL
210An attempt was made to add a record to a fixed-length database that
211was too large to fit.
212.El
213.Sh SEE ALSO
214.Xr btree 3 ,
215.Xr dbopen 3 ,
216.Xr hash 3 ,
217.Xr mpool 3
218.Rs
219.%T "Document Processing in a Relational Database System"
220.%A Michael Stonebraker
221.%A Heidi Stettner
222.%A Joseph Kalash
223.%A Antonin Guttman
224.%A Nadene Lynn
225.%R "Memorandum No. UCB/ERL M82/32"
226.%D May 1982
227.Re
228.Sh BUGS
229Only big and little endian byte order is supported.
230