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    3: <meta name=Title content="Session Three: lonsql (Gerd)">
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    5: <title>Session Three: lonsql (Gerd)</title>
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   15: <div class=Section1> 
   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"'>&nbsp;&nbsp;&nbsp;&nbsp; </span> 
   26:     title </p>
   27:   <p> 2.<span style='font:7.0pt "Times New Roman"'>&nbsp;&nbsp;&nbsp;&nbsp; </span> 
   28:     author </p>
   29:   <p> 3.<span style='font:7.0pt "Times New Roman"'>&nbsp;&nbsp;&nbsp;&nbsp; </span> 
   30:     subject </p>
   31:   <p> 4.<span style='font:7.0pt "Times New Roman"'>&nbsp;&nbsp;&nbsp;&nbsp; </span> 
   32:     notes </p>
   33:   <p> 5.<span style='font:7.0pt "Times New Roman"'>&nbsp;&nbsp;&nbsp;&nbsp; </span> 
   34:     abstract </p>
   35:   <p> 6.<span style='font:7.0pt "Times New Roman"'>&nbsp;&nbsp;&nbsp;&nbsp; </span> 
   36:     mime </p>
   37:   <p> 7.<span style='font:7.0pt "Times New Roman"'>&nbsp;&nbsp;&nbsp;&nbsp; </span> 
   38:     language </p>
   39:   <p> 8.<span style='font:7.0pt "Times New Roman"'>&nbsp;&nbsp;&nbsp;&nbsp; </span> 
   40:     creationdate </p>
   41:   <p> 9.<span style='font:7.0pt "Times New Roman"'>&nbsp;&nbsp;&nbsp;&nbsp; </span> 
   42:     lastrevisiondate </p>
   43:   <p> 10.<span style='font:7.0pt "Times New Roman"'>&nbsp; </span> owner </p>
   44:   <p> 11.<span style='font:7.0pt "Times New Roman"'>&nbsp; </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 &quot;metadata&quot;. 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>&nbsp;&nbsp;&nbsp; lonc= loncapa client process&nbsp;&nbsp;&nbsp; A-lonc= 
   61:     a lonc process on Server A</p>
   62:   <p>&nbsp;&nbsp;&nbsp; lond= loncapa daemon process</p>
   63:   <p><span style='font-family:"Courier New"'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 
   64:     database command</span></p>
   65:   <p><span style='font-family:"Courier New"'>&nbsp;&nbsp;&nbsp; A-lonc&nbsp; --------TCP/IP----------------&gt; 
   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 &quot;do its stuff&quot;, or in other words, perform the conceivably 
   69:     sophisticated, data-intensive, time-sucking database transaction.&nbsp; 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.&nbsp; This 
   77:     daemon process is called &quot;lonsql&quot;.</span></p>
   78:   <p>&nbsp; So,</p>
   79:   <p><span style='font-family:"Courier New"'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 
   80:     database command</span></p>
   81:   <p><span style='font-family:"Courier New"'>&nbsp; A-lonc&nbsp; ---------TCP/IP-----------------&gt; 
   82:     B-lond =====&gt; B-lonsql</span></p>
   83:   <p><span style='font-family:"Courier New"'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 
   84:     &lt;---------------------------------/&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 
   85:     |</span></p>
   86:   <p><span style='font-family:"Courier New"'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 
   87:     &quot;ok, I'll get back to you...&quot;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 
   88:     |</span></p>
   89:   <p><span style='font-family:"Courier New"'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 
   90:     |</span></p>
   91:   <p><span style='font-family:"Courier New"'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 
   92:     &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;/</span></p>
   93:   <p><span style='font-family:"Courier New"'>&nbsp; A-lond&nbsp; &lt;-------------------------------&nbsp; 
   94:     B-lonc&nbsp;&nbsp; &lt;======</span></p>
   95:   <p><span style='font-family:"Courier New"'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 
   96:     &quot;Guess what? I have the result!&quot;</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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