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1: <html>
2:
3: <head>
4:
5: <meta name=Title content="Session Three: lonsql (Gerd)">
6:
7: <meta http-equiv=Content-Type content="text/html; charset=macintosh">
8:
9: <title>Session Three: lonsql (Gerd)</title>
10:
11: <style><!--
12:
13: .Section1
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15: {page:Section1;}
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17: .Section2
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19: {page:Section2;}
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21: -->
22:
23: </style>
24:
25: </head>
26:
27: <body bgcolor=#FFFFFF class="Normal" lang=EN-US>
28:
29: <div class=Section1>
30:
31: <h2>Session Three: lonsql (Gerd)</h2>
32:
33: <p>This section describes issues associated with LON-CAPA and a SQL database.</p>
34:
35: <p>The SQL database in LON-CAPA is used for catalog searches against resource
36:
37: metadata only. The authoritative version of the resource metadata is Ð as
38:
39: discussed Ð an XML-file on the normal file system (same file name as resource
40:
41: plus Ò.metaÓ). The SQL-database is a cache of these files, and can be reconstructed
42:
43: from the XML files at any time.</p>
44:
45: <p>The current database is implemented assuming a non-adjustable architecture
46:
47: involving these data fields (specific to each version of a resource). </p>
48:
49: <p> 1.<span style='font:7.0pt "Times New Roman"'> </span>
50:
51: title </p>
52:
53: <p> 2.<span style='font:7.0pt "Times New Roman"'> </span>
54:
55: author </p>
56:
57: <p> 3.<span style='font:7.0pt "Times New Roman"'> </span>
58:
59: subject </p>
60:
61: <p> 4.<span style='font:7.0pt "Times New Roman"'> </span>
62:
63: notes </p>
64:
65: <p> 5.<span style='font:7.0pt "Times New Roman"'> </span>
66:
67: abstract </p>
68:
69: <p> 6.<span style='font:7.0pt "Times New Roman"'> </span>
70:
71: mime </p>
72:
73: <p> 7.<span style='font:7.0pt "Times New Roman"'> </span>
74:
75: language </p>
76:
77: <p> 8.<span style='font:7.0pt "Times New Roman"'> </span>
78:
79: creationdate </p>
80:
81: <p> 9.<span style='font:7.0pt "Times New Roman"'> </span>
82:
83: lastrevisiondate </p>
84:
85: <p> 10.<span style='font:7.0pt "Times New Roman"'> </span> owner </p>
86:
87: <p> 11.<span style='font:7.0pt "Times New Roman"'> </span> copyright </p>
88:
89: <h3><a name="_Toc421867145">Purpose within LON-CAPA</a></h3>
90:
91: <p>LON-CAPA is meant to distribute A LOT of educational content to A LOT of
92:
93: people. It is ineffective to directly rely on contents within the ext2 filesystem
94:
95: to be speedily scanned for on-the-fly searches of content descriptions. (Simply
96:
97: put, it takes a cumbersome amount of time to open, read, analyze, and close
98:
99: thousands of files.) </p>
100:
101: <p>The solution is to hash-index various data fields that are descriptive of
102:
103: the educational resources on a LON-CAPA server machine. Descriptive data fields
104:
105: are referred to as "metadata". The question then arises as to how
106:
107: this metadata is handled in terms of the rest of the LON-CAPA network without
108:
109: burdening client and daemon processes. I now answer this question in the format
110:
111: of Problem and Solution below. </p>
112:
113: <p><b>PROBLEM SITUATION:</b><span style='font-weight:normal'> If Server A wants
114:
115: data from Server B, Server A uses a lonc process to send a database command
116:
117: to a Server B lond process.</span></p>
118:
119: <p> lonc= loncapa client process A-lonc=
120:
121: a lonc process on Server A</p>
122:
123: <p> lond= loncapa daemon process</p>
124:
125: <p><span style='font-family:"Courier New"'>
126:
127: database command</span></p>
128:
129: <p><span style='font-family:"Courier New"'> A-lonc --------TCP/IP---------------->
130:
131: B-lond</span></p>
132:
133: <p>The problem emerges that A-lonc and B-lond are kept waiting for the MySQL
134:
135: server to "do its stuff", or in other words, perform the conceivably
136:
137: sophisticated, data-intensive, time-sucking database transaction. By
138:
139: tying up a lonc and lond process, this significantly cripples the capabilities
140:
141: of LON-CAPA servers. </p>
142:
143: <p>While commercial databases have a variety of features that ATTEMPT to deal
144:
145: with this, freeware databases are still experimenting and exploring with different
146:
147: schemes with varying degrees of performance stability.</p>
148:
149: <p><b>THE SOLUTION:</b><span style='font-weight:normal'> A separate daemon process
150:
151: was created that B-lond works with to handle database requests. This
152:
153: daemon process is called "lonsql".</span></p>
154:
155: <p> So,</p>
156:
157: <p><span style='font-family:"Courier New"'>
158:
159: database command</span></p>
160:
161: <p><span style='font-family:"Courier New"'> A-lonc ---------TCP/IP----------------->
162:
163: B-lond =====> B-lonsql</span></p>
164:
165: <p><span style='font-family:"Courier New"'>
166:
167: <---------------------------------/
168:
169: |</span></p>
170:
171: <p><span style='font-family:"Courier New"'>
172:
173: "ok, I'll get back to you..."
174:
175: |</span></p>
176:
177: <p><span style='font-family:"Courier New"'>
178:
179: |</span></p>
180:
181: <p><span style='font-family:"Courier New"'>
182:
183: /</span></p>
184:
185: <p><span style='font-family:"Courier New"'> A-lond <-------------------------------
186:
187: B-lonc <======</span></p>
188:
189: <p><span style='font-family:"Courier New"'>
190:
191: "Guess what? I have the result!"</span></p>
192:
193: <p>Of course, depending on success or failure, the messages may vary, but the
194:
195: principle remains the same where a separate pool of children processes (lonsql's)
196:
197: handle the MySQL database manipulations.</p>
198:
199: </div>
200:
201: <br
202:
203: clear=ALL style='page-break-before:always;'>
204:
205: <div class=Section2> </div>
206:
207: </body>
208:
209: </html>
210:
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