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Diff for /loncom/lonsql between versions 1.53 and 1.58

version 1.53, 2002/09/09 14:04:02 version 1.58, 2004/05/03 16:20:57
Line 39  lonsql - LON TCP-MySQL-Server Daemon for Line 39  lonsql - LON TCP-MySQL-Server Daemon for
 This script should be run as user=www.    This script should be run as user=www.  
 Note that a lonsql.pid file contains the pid of the parent process.  Note that a lonsql.pid file contains the pid of the parent process.
   
 =head1 DESCRIPTION  =head1 OVERVIEW
   
 lonsql is many things to many people.  To me, it is a source file in need  =head2 Purpose within LON-CAPA
 of documentation.  
   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.)
   
   The solution is to index various data fields that are descriptive of
   the educational resources on a LON-CAPA server machine in a
   database. 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.
   
   The obvious solution, using lonc to send a query to a lond process,
   doesn't work so well in general as you can see in the following
   example:
   
       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.
   
   The solution is to offload the work onto another process, and use
   lonc and lond just for requests and notifications of completed
   processing:
   
                   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.
   
   Thus, lonc and lond spend effectively no time waiting on results from
   the database.
   
 =head1 Internals  =head1 Internals
   
Line 54  use strict; Line 103  use strict;
   
 use lib '/home/httpd/lib/perl/';  use lib '/home/httpd/lib/perl/';
 use LONCAPA::Configuration;  use LONCAPA::Configuration;
   use LONCAPA::lonmetadata();
   
 use IO::Socket;  use IO::Socket;
 use Symbol;  use Symbol;
Line 166  unless ($dbh = DBI->connect("DBI:mysql:l Line 216  unless ($dbh = DBI->connect("DBI:mysql:l
     my $subj="LON: $perlvar{'lonHostID'} Cannot connect to database!";      my $subj="LON: $perlvar{'lonHostID'} Cannot connect to database!";
     system("echo 'Cannot connect to MySQL database!' |".      system("echo 'Cannot connect to MySQL database!' |".
            " mailto $emailto -s '$subj' > /dev/null");             " mailto $emailto -s '$subj' > /dev/null");
   
       open(SMP,'>/home/httpd/html/lon-status/mysql.txt');
       print SMP 'time='.time.'&mysql=defunct'."\n";
       close(SMP);
   
     exit 1;      exit 1;
 } else {  } else {
     $dbh->disconnect;      $dbh->disconnect;
Line 421  sub do_sql_query { Line 476  sub do_sql_query {
         #prepare and execute the query          #prepare and execute the query
         my $sth = $dbh->prepare($query);          my $sth = $dbh->prepare($query);
         unless ($sth->execute()) {          unless ($sth->execute()) {
             &logthis("<font color=blue>WARNING: ".              &logthis('<font color=blue>'.
                      "Could not retrieve from database: $@</font>");                       'WARNING: Could not retrieve from database:'.
                        $sth->errstr().'</font>');
         } else {          } else {
             my $aref=$sth->fetchall_arrayref;              my $aref=$sth->fetchall_arrayref;
             foreach my $row (@$aref) {              foreach my $row (@$aref) {
Line 881  sub DISCONNECT { Line 937  sub DISCONNECT {
 }  }
   
   
   
   
   
   
   
   
   
   
   
 # ----------------------------------- POD (plain old documentation, CPAN style)  
   
 =pod  =pod
   
 =back  =back
Removed from v.1.53  
changed lines
  Added in v.1.58

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