1:- module(bdb_wrapper,
2 [
3 bdb_base/1,
4 bdb_erase/1,
5 bdb_erase/2,
6 bdb_retrieve/3,
7 bdb_store/3
8 ]).
48%------------------------------------------------------------------------------------- 49 50:- use_module(library(codesio), 51 [ 52 format_to_codes/3 53 ]). 54 55:- use_module(library(filesex), 56 [ 57 delete_directory_and_contents/1 58 ]). 59 60:- dynamic swi_bdb_base/1. 61:- volatile swi_bdb_base/1. 62 63%-------------------------------------------------------------------------------------
BasePath Atom identifying the base path for Berkeley DB's persistence files
72bdb_base(BasePath) :-
73
74 (var(BasePath) ->
75 swi_bdb_base(BasePath)
76 ;
77 % register the base path for Berkeley DB (make sure it is '/'-terminated)
78 (retract(swi_bdb_base(_)) ; true),
79 !,
80 (sub_atom(BasePath, _, 1, 0, '/') ->
81 BdbPath = BasePath
82 ;
83 atom_concat(BasePath, '/', BdbPath)
84 ),
85 assertz(swi_bdb_base(BdbPath))
86 ),
87
88 % make sure path exists
89 (exists_directory(BasePath) ->
90 true
91 ;
92 make_directory(BasePath)
93 ).
103bdb_store(TagSet, DataSet, Data) :-
104
105 % obtain the storage filepath for this dataset
106 storage_path(TagSet, DataSet, DsPath),
107
108 % create base directory, if necessary
109 file_directory_name(DsPath, BaseDir),
110 (exists_directory(BaseDir) ->
111 true
112 ;
113 make_directory(BaseDir)
114 ),
115
116 !,
117 % fail point (create the database)
118 catch(bdb_open(DsPath, update, DbRef, []), _, fail),
119
120 !,
121 % fail point (store the data)
122 catch(bdb_put(DbRef, data, Data), _, fail),
123
124 !,
125 % fail point (close the database)
126 catch(bdb_close(DbRef), _, fail).
136bdb_retrieve(TagSet, DataSet, Data) :-
137
138 % obtain the storage filepath for this dataset
139 storage_path(TagSet, DataSet, DsPath),
140
141 !,
142 % fail point (open the database)
143 catch(bdb_open(DsPath, read, DbRef, []), _, fail),
144
145 !,
146 % fail point (retrieve the data)
147 catch(bdb_get(DbRef, data, Data), _, fail),
148
149 !,
150 % fail point (close the database)
151 catch(bdb_close(DbRef), _, fail).
159bdb_erase(DataSet) :-
160
161 % obtain the base storage location
162 storage_path('*', DataSet, DsPath),
163 file_directory_name(DsPath, BaseDir),
164
165 % delete storage directory, if necessary
166 (exists_directory(BaseDir) ->
167 delete_directory_and_contents(BaseDir)
168 ;
169 true
170 ).178bdb_erase(TagSet, DataSet) :- 179 180 % obtain the storage filepath for this dataset 181 storage_path(TagSet, DataSet, DsPath), 182 183 % delete it, if necessary 184 (\+ exists_file(DsPath) ; (delete_file(DsPath))). 185 186%-------------------------------------------------------------------------------------
196storage_path(TagSet, DataSet, DsPath) :-
197
198 % obtain the registered base path
199 (swi_bdb_base(BasePath) ; BasePath = ''),
200 !,
201
202 % build the base directory
203 atom_concat(BasePath, DataSet, BaseDir),
204
205 % build the storage path
206 format_to_codes('~a/~a.dbd', [BaseDir,TagSet], Codes),
207 atom_codes(DsPath, Codes)
Persistence using Berkeley DB
This module provides a simple, minimalistic approach to implementing persistence on the SWI-Prolog platform, by means of the Berkeley DB utility package. The target data is organized in DataSets. A DataSet is comprised of one or more TagSets, and a TagSet is a named collection of Prolog data.
Berkeley DB is an open-source software library intended to provide a high-performance embedded database for key/value data. The database storage is organized as a directory tree, starting with a root path specified with bdb_path/1.
Being an embedded database implies that the library provides access to files containing one or more database tables. These tables are always binary, mapping keys to values. The SWI-Prolog interface to Berkeley DB allows for fast storage of arbitrary Prolog terms, including cycles and constraints.
On Windows, the package Berkeley DB for Windows version 6.2.38 must have been installed. The installers db-6.2.28_86.msi (32 bits) and db-6.2.28_64.msi (64 bits) may be obtained directly at the Oracle Berkeley DB site.
Most Linux distributions already carry the Berkeley DB library by default. Additionally, on Linux environments SWI-Prolog requires that the package swi-prolog-bdb be installed.
The Linux db-util package is fully compatible with the database structure created by SWI-Prolog through Berkeley DB. For the db-util manpages, please refer to https://manpages.debian.org/jessie/db-util/index.html .
Please, refer to https://www.swi-prolog.org/pldoc/doc/_SWI_/library/bdb.pl for additional instructions on how to use Berkeley DB.