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! 16: <h2>Session Three: lonsql (Gerd)</h2>
! 17: <p>This section describes issues associated with LON-CAPA and a SQL database.</p>
! 18: <p>The SQL database in LON-CAPA is used for catalog searches against resource
! 19: metadata only. The authoritative version of the resource metadata is Ð as
! 20: discussed Ð an XML-file on the normal file system (same file name as resource
! 21: plus Ò.metaÓ). The SQL-database is a cache of these files, and can be reconstructed
! 22: from the XML files at any time.</p>
! 23: <p>The current database is implemented assuming a non-adjustable architecture
! 24: involving these data fields (specific to each version of a resource). </p>
! 25: <p> 1.<span style='font:7.0pt "Times New Roman"'> </span>
! 26: title </p>
! 27: <p> 2.<span style='font:7.0pt "Times New Roman"'> </span>
! 28: author </p>
! 29: <p> 3.<span style='font:7.0pt "Times New Roman"'> </span>
! 30: subject </p>
! 31: <p> 4.<span style='font:7.0pt "Times New Roman"'> </span>
! 32: notes </p>
! 33: <p> 5.<span style='font:7.0pt "Times New Roman"'> </span>
! 34: abstract </p>
! 35: <p> 6.<span style='font:7.0pt "Times New Roman"'> </span>
! 36: mime </p>
! 37: <p> 7.<span style='font:7.0pt "Times New Roman"'> </span>
! 38: language </p>
! 39: <p> 8.<span style='font:7.0pt "Times New Roman"'> </span>
! 40: creationdate </p>
! 41: <p> 9.<span style='font:7.0pt "Times New Roman"'> </span>
! 42: lastrevisiondate </p>
! 43: <p> 10.<span style='font:7.0pt "Times New Roman"'> </span> owner </p>
! 44: <p> 11.<span style='font:7.0pt "Times New Roman"'> </span> copyright </p>
! 45: <h3><a name="_Toc421867145">Purpose within LON-CAPA</a></h3>
! 46: <p>LON-CAPA is meant to distribute A LOT of educational content to A LOT of
! 47: people. It is ineffective to directly rely on contents within the ext2 filesystem
! 48: to be speedily scanned for on-the-fly searches of content descriptions. (Simply
! 49: put, it takes a cumbersome amount of time to open, read, analyze, and close
! 50: thousands of files.) </p>
! 51: <p>The solution is to hash-index various data fields that are descriptive of
! 52: the educational resources on a LON-CAPA server machine. Descriptive data fields
! 53: are referred to as "metadata". The question then arises as to how
! 54: this metadata is handled in terms of the rest of the LON-CAPA network without
! 55: burdening client and daemon processes. I now answer this question in the format
! 56: of Problem and Solution below. </p>
! 57: <p><b>PROBLEM SITUATION:</b><span style='font-weight:normal'> If Server A wants
! 58: data from Server B, Server A uses a lonc process to send a database command
! 59: to a Server B lond process.</span></p>
! 60: <p> lonc= loncapa client process A-lonc=
! 61: a lonc process on Server A</p>
! 62: <p> lond= loncapa daemon process</p>
! 63: <p><span style='font-family:"Courier New"'>
! 64: database command</span></p>
! 65: <p><span style='font-family:"Courier New"'> A-lonc --------TCP/IP---------------->
! 66: B-lond</span></p>
! 67: <p>The problem emerges that A-lonc and B-lond are kept waiting for the MySQL
! 68: server to "do its stuff", or in other words, perform the conceivably
! 69: sophisticated, data-intensive, time-sucking database transaction. By
! 70: tying up a lonc and lond process, this significantly cripples the capabilities
! 71: of LON-CAPA servers. </p>
! 72: <p>While commercial databases have a variety of features that ATTEMPT to deal
! 73: with this, freeware databases are still experimenting and exploring with different
! 74: schemes with varying degrees of performance stability.</p>
! 75: <p><b>THE SOLUTION:</b><span style='font-weight:normal'> A separate daemon process
! 76: was created that B-lond works with to handle database requests. This
! 77: daemon process is called "lonsql".</span></p>
! 78: <p> So,</p>
! 79: <p><span style='font-family:"Courier New"'>
! 80: database command</span></p>
! 81: <p><span style='font-family:"Courier New"'> A-lonc ---------TCP/IP----------------->
! 82: B-lond =====> B-lonsql</span></p>
! 83: <p><span style='font-family:"Courier New"'>
! 84: <---------------------------------/
! 85: |</span></p>
! 86: <p><span style='font-family:"Courier New"'>
! 87: "ok, I'll get back to you..."
! 88: |</span></p>
! 89: <p><span style='font-family:"Courier New"'>
! 90: |</span></p>
! 91: <p><span style='font-family:"Courier New"'>
! 92: /</span></p>
! 93: <p><span style='font-family:"Courier New"'> A-lond <-------------------------------
! 94: B-lonc <======</span></p>
! 95: <p><span style='font-family:"Courier New"'>
! 96: "Guess what? I have the result!"</span></p>
! 97: <p>Of course, depending on success or failure, the messages may vary, but the
! 98: principle remains the same where a separate pool of children processes (lonsql's)
! 99: handle the MySQL database manipulations.</p>
! 100: </div>
! 101: <br
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! 103: <div class=Section2> </div>
! 104: </body>
! 105: </html>
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