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version 1.2, 2001/02/07 13:02:38 version 1.4, 2001/02/10 18:38:37
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 Scott Harrison  Scott Harrison
 </P>  </P>
 <P>  <P>
 Last updated: 02/07/2001  Last updated: 02/10/2001
 </P>  </P>
 <P>  <P>
 This file describes issues associated with LON-CAPA  This file describes issues associated with LON-CAPA
Line 16  and a SQL database. Line 16  and a SQL database.
 </P>  </P>
 <H3>Latest HOWTO</H3>  <H3>Latest HOWTO</H3>
 <P>  <P>
   <UL>
   <LI>Current status of documentation</LI>
   <LI>Current status of implementation</LI>
   <LI>Purpose within LON-CAPA</LI>
   <LI>Installation</LI>
   <LI>Installation from source</LI>
   <LI>Configuration (automated)</LI>
   <LI>Manual configuration</LI>
   <LI>Testing</LI>
   <LI>Example sections of code relevant to LON-CAPA</LI>
   </UL>
   </P>
   <H3>Current status of documentation</H3>
   <P>
 I am going to begin documentation by inserting what notes  I am going to begin documentation by inserting what notes
 I have into this file.  I will be subsequently rearranging  I have into this file.  I will be subsequently rearranging
 them and editting them based on the tests that I conduct.  them and editing them based on the tests that I conduct.
 I am trying to make sure that documentation, installation,  I am trying to make sure that documentation, installation,
 and run-time issues are all consistent and correct.  The  and run-time issues are all consistent and correct.  The
 current status of everything is that it works and has  current status of everything is that it works and has
 been minimally tested, but things need to be cleaned up  been minimally tested, but things need to be cleaned up
 and checked again!  and checked again!
 </P>  </P>
   <H3>Current status of implementation</H3>
   <P>
   Right now, a lot of "feasibility" work has been done.
   Recipes for manual installation and configuration have
   been gathered.  Network connectivity of lond->lonsql->lond->lonc
   type tests have been performed.  A binary installation
   has been compiled in an RPM (LON-CAPA-mysql).
   The most lacking test in terms of feasibility has
   been looking at benchmarks to analyze the load at which
   the SQL database can efficiently allow many users to
   make simultaneous requests of the metadata database.
   </P>
   <P>
   Documentation has been pieced together over time.  But,
   as mentioned in the previous section, it needs an
   overhaul.
   </P>
   <P>
   The binary installation has some quirks associated with it.
   Some of the user permissions are wrong, although this is
   benign.  Also, other options of binary installation (such
   as using binary RPMs put together by others) were dismissed
   given the difficulty of getting differing combinations of
   these external RPMs to work together.
   </P>
   <P>
   Most configuration questions have been initially worked out
   to the point of getting this SQL software component working,
   however there may be more optimal approaches than currently
   exist.
   </P>
   <H3>Purpose within LON-CAPA</H3>
   <P>
   LON-CAPA is meant to distribute A LOT of educational content
   to A LOT of people.  It is ineffective to directly rely on contents
   within the ext2 filesystem to be speedily scanned for 
   on-the-fly searches of content descriptions.  (Simply put,
   it takes a cumbersome amount of time to open, read, analyze, and
   close thousands of files.)
   </P>
   <P>
   The solution is to hash-index various data fields that are
   descriptive of the educational resources on a LON-CAPA server
   machine.  Descriptive data fields are referred to as
   "metadata".  The question then arises as to how this metadata
   is handled in terms of the rest of the LON-CAPA network
   without burdening client and daemon processes.  I now
   answer this question in the format of Problem and Solution
   below.
   </P>
   <P>
   <PRE>
   PROBLEM SITUATION:
   
     If Server A wants data from Server B, Server A uses a lonc process to
     send a database command to a Server B lond process.
       lonc= loncapa client process    A-lonc= a lonc process on Server A
       lond= loncapa daemon process
   
                    database command
       A-lonc  --------TCP/IP----------------> B-lond
   
     The problem emerges that A-lonc and B-lond are kept waiting for the
     MySQL server to "do its stuff", or in other words, perform the conceivably
     sophisticated, data-intensive, time-sucking database transaction.  By tying
     up a lonc and lond process, this significantly cripples the capabilities
     of LON-CAPA servers. 
   
     While commercial databases have a variety of features that ATTEMPT to
     deal with this, freeware databases are still experimenting and exploring
     with different schemes with varying degrees of performance stability.
   
   THE SOLUTION:
   
     A separate daemon process was created that B-lond works with to
     handle database requests.  This daemon process is called "lonsql".
   
     So,
                   database command
     A-lonc  ---------TCP/IP-----------------> B-lond =====> B-lonsql
            <---------------------------------/                |
              "ok, I'll get back to you..."                    |
                                                               |
                                                               /
     A-lond  <-------------------------------  B-lonc   <======
              "Guess what? I have the result!"
   
     Of course, depending on success or failure, the messages may vary,
     but the principle remains the same where a separate pool of children
     processes (lonsql's) handle the MySQL database manipulations.
   </PRE>
   </P>
   <H3>Installation</H3>
   <P>
   Installation of the LON-CAPA SQL database normally occurs
   by default when using the LON-CAPA installation CD
   (see http://install.lon-capa.org).  It is installed
   as the LON-CAPA-mysql RPM.  This RPM encodes for the MySQL
   engine and related perl interfaces (Perl::DBI, Perl::Msql-Mysql).
   </P>
   <P>
   The three components of a MySQL installation for the
   LON-CAPA system are further described immediately below.
   <TABLE BORDER="0">
   <TR><TD COLSPAN="2"><STRONG>Perl::DBI module</STRONG>-
   the API "front-end"...</TD></TR>
   <TR><TD WIDTH="10%"></TD><TD>database interface module for organizing generic
   database commands which are independent of specific
   database implementation (such as MySQL, mSQL, Postgres, etc).
   </TD></TR>
   <TR><TD COLSPAN="2"><STRONG>Perl::MySQL module</STRONG>-
   the API "mid-section"...</TD></TR>
   <TR><TD WIDTH="10%"></TD><TD>the module to directly interface with the actual
   MySQL database engine</TD></TR>
   <TR><TD COLSPAN="2"><STRONG>MySQL database engine</STRONG>-
   the "back-end"...</TD></TR>
   <TR><TD WIDTH="10%"></TD><TD>the binary installation (compiled either
   from source or pre-compiled file listings) which provides the
   actual MySQL functionality on the system</TD></TR>
   </TABLE>
   </P>
   <H3>Installation from source</H3>
   <P>
   The following set of tarballs was found to work together
   properly on a LON-CAPA RedHat 6.2 system:
   <UL>
   <LI>DBI-1.13.tar.gz
   <LI>Msql-Mysql-modules-1.2209.tar.gz
   <LI>mysql-3.22.32.tar.gz
   </UL>
   </P>
   <P>
   Installation was simply a matter of following the instructions
   and typing the several "make" commands for each 
   </P>
   <H3>Configuration (automated)</H3>
   <P>
   Not yet developed.  This will be part of an interface
   present on LON-CAPA systems that can be launched by
   entering the command <TT>/usr/sbin/loncapaconfig</TT>.
   </P>
   <H3>Manual configuration</H3>
   <P>
   This is not complete.
   </P>
   <P>
   <STRONG>Starting the mysql daemon</STRONG>: Login on the Linux
   system as user 'www'.  Enter the command
   <TT>/usr/local/bin/safe_mysqld &</TT>
   </P>
   <P>
   <STRONG>Set a password for 'root'</STRONG>:
   <TT>/usr/local/bin/mysqladmin -u root password 'new-password'</TT>
   </P>
   <P>
   <STRONG>Adding a user</STRONG>:  Start the mysql daemon.  Login to the
   mysql system as root (<TT>mysql -u root -p mysql</TT>)
   and enter the right password (for instance 'newmysql').  Add the user
   www
   <PRE>
   INSERT INTO user (Host, User, Password)
   VALUES ('localhost','www',password('newmysql'));
   </PRE>
   </P>
   <P>
   <STRONG>Granting privileges to user 'www'</STRONG>:
   <PRE>
   GRANT ALL PRIVILEGES ON *.* TO www@localhost;
   FLUSH PRIVILEGES;
   </PRE>
   </P>
   <P>
   <STRONG>Set the SQL server to start upon system startup</STRONG>:
   Copy support-files/mysql.server to the right place on the system
   (/etc/rc.d/...).
   </P>
   <H3>Testing</H3>
   <P>
   Not yet documented or formalized.
   </P>
   <H3>Example sections of code relevant to LON-CAPA</H3>
   <P>
   </P>
   
   <H1>Old notes</H1>
   
 <H3>How to add a user to the SQL database</H3>  <H3>How to add a user to the SQL database</H3>
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