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! 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>
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! 51: title </p>
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! 53: <p> 2.<span style='font:7.0pt "Times New Roman"'> </span>
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! 55: author </p>
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! 57: <p> 3.<span style='font:7.0pt "Times New Roman"'> </span>
! 58:
! 59: subject </p>
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! 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>
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! 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
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! 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
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! 109: burdening client and daemon processes. I now answer this question in the format
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! 111: of Problem and Solution below. </p>
! 112:
! 113: <p><b>PROBLEM SITUATION:</b><span style='font-weight:normal'> If Server A wants
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! 115: data from Server B, Server A uses a lonc process to send a database command
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! 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>
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