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1 | .\" Copyright (c) 1990, 1993 |
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32 | .\" @(#)recno.3 8.5 (Berkeley) 8/18/94 | |
33 | .\" | |
0ed55ece | 34 | .TH RECNO 3 1994-08-18 "" "Linux Programmer's Manual" |
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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 | |
0daa9e92 | 47 | .I dbopen |
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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 | |
31e9a9ec | 51 | .BR dbopen (3), |
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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 | |
b9f02710 | 67 | .nf |
fea681da | 68 | typedef struct { |
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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; | |
fea681da | 76 | } RECNOINFO; |
b9f02710 | 77 | .fi |
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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 | |
31e9a9ec | 134 | .BR btree (3) |
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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, | |
2c5f1089 | 160 | as if specified as the filename for a dbopen of a btree file. |
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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 | |
75b94dc3 | 178 | (e.g., fixed record length or byte separator value) must be explicitly |
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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 | |
31e9a9ec | 194 | .BR dbopen (3) |
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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. | |
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200 | .SH BUGS |
201 | Only big and little endian byte order is supported. | |
fea681da | 202 | .SH "SEE ALSO" |
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203 | .BR btree (3) |
204 | .BR dbopen (3), | |
205 | .BR hash (3), | |
d8aaa1d3 | 206 | .BR mpool (3) |
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207 | .sp |
208 | .IR "Document Processing in a Relational Database System" , | |
209 | Michael Stonebraker, Heidi Stettner, Joseph Kalash, Antonin Guttman, | |
210 | Nadene Lynn, Memorandum No. UCB/ERL M82/32, May 1982. |