August, 29 2000; Scott Harrison; LON-CAPA These are notes related to a Perl interface and MySQL server installation on Redhat 6.1 and 6.2 boxes. (Guy Albertelli and Harsha Jagasia contributed significantly to this.) ******************** * MySQL COMPONENTS * ******************** There are three components to an effective MySQL installation for the LON-CAPA system. Perl::DBI module- the API "front-end"... database interface module for organizing generic database commands which are independent of specific database implementation (such as MySQL, mSQL, Postgres, etc). Perl::MySQL module- the API "mid-section"... the module to directly interface with the actual MySQL database engine MySQL database engine- the "back-end"... the binary installation (compiled either from source or pre-compiled file listings) which provides the actual MySQL functionality on the system RedHat Installation- Initially done from source: DBI-1.13.tar.gz Msql-Mysql-modules-1.2209.tar.gz mysql-3.22.32.tar.gz I am now using pre-compiled file listings. There were problems with using the RedHat packages since the three different RedHat packages were somewhat noncompatible with each other in terms of expected file locations. (The Debian linux distribution, on the other hand, has a working set of these packages). Regardless of how we install these three components, there still remain certain things which need to happen for the configuration. ***************** * CONFIGURATION * ***************** (Note: SOMEPASSWORD is actually set to another text string on the current LON-CAPA systems.) Configuration is needed to generate the necessary functionality for the MySQL system with LON-CAPA. The functionality needed can be understood from this example line of perl code from "lonsql". $dbh = DBI->connect( "DBI:mysql:loncapa", "www", "SOMEPASSWORD", { RaiseError =>0,PrintError=>0}); There is an obvious need to CONNECT to the database, and in order to do this, there must be: a RUNNING mysql daemon; a DATABASE named "loncapa"; a USER named "www"; and an ABILITY for LON-CAPA on one machine to access SQL database on another machine; So, here are some notes on implementing these configurations. ** RUNNING mysql daemon (safe_mysqld method) The recommended way to run the MySQL daemon is as a non-root user (probably www)... so, 1) login as user www on the linux machine 2) start the mysql daemon as /usr/local/bin/safe_mysqld & safe_mysqld only works if the local installation of MySQL is set to the right directory permissions which I found to be: chown www:users /usr/local/var/mysql chown www:users /usr/local/lib/mysql chown -R www:users /usr/local/mysql chown www:users /usr/local/include/mysql chown www:users /usr/local/var ** DATABASE named "loncapa" As user www, run this command mysql -u root -p mysql enter the password as SOMEPASSWORD This allows you to manually enter MySQL commands. The MySQL command to generate the loncapa DATABASE is: CREATE DATABASE loncapa; ** USER named "www" As user www, run this command mysql -u root -p mysql enter the password as SOMEPASSWORD To add the user www to the MySQL server, and grant all privileges on *.* to www@localhost identified by 'SOMEPASSWORD' with grant option; INSERT INTO user (Host, User, Password) VALUES ('localhost','www',password('SOMEPASSWORD')); GRANT ALL PRIVILEGES ON *.* TO www@localhost; FLUSH PRIVILEGES; ** ABILITY for LON-CAPA machines to communicate with SQL databases on other LON-CAPA machines This is a little more intricate than might first be expected (and I probably won't do a perfect job reciting everything in this short synopsis). Because LON-CAPA machines will likely be handling many SQL requests at a time, there were some problems with current MySQL capabilities. 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. Here are excerpts of code which implement the above handling: **LONSQL A subroutine from "lonsql" which establishes a child process for handling database interactions. sub make_new_child { my $pid; my $sigset; # block signal for fork $sigset = POSIX::SigSet->new(SIGINT); sigprocmask(SIG_BLOCK, $sigset) or die "Can't block SIGINT for fork: $!\n"; die "fork: $!" unless defined ($pid = fork); if ($pid) { # Parent records the child's birth and returns. sigprocmask(SIG_UNBLOCK, $sigset) or die "Can't unblock SIGINT for fork: $!\n"; $children{$pid} = 1; $children++; return; } else { # Child can *not* return from this subroutine. $SIG{INT} = 'DEFAULT'; # make SIGINT kill us as it did before # unblock signals sigprocmask(SIG_UNBLOCK, $sigset) or die "Can't unblock SIGINT for fork: $!\n"; #open database handle # making dbh global to avoid garbage collector unless ( $dbh = DBI->connect("DBI:mysql:loncapa","www","SOMEPASSWORD",{ RaiseError =>0,PrintError=>0}) ) { my $st=120+int(rand(240)); &logthis("WARNING: Couldn't connect to database ($st secs): $@"); print "database handle error\n"; sleep($st); exit; }; # make sure that a database disconnection occurs with ending kill signals $SIG{TERM}=$SIG{INT}=$SIG{QUIT}=$SIG{__DIE__}=\&DISCONNECT; # handle connections until we've reached $MAX_CLIENTS_PER_CHILD for ($i=0; $i < $MAX_CLIENTS_PER_CHILD; $i++) { $client = $server->accept() or last; # do something with the connection $run = $run+1; my $userinput = <$client>; chomp($userinput); my ($conserver,$querytmp)=split(/&/,$userinput); my $query=unescape($querytmp); #send query id which is pid_unixdatetime_runningcounter $queryid = $thisserver; $queryid .="_".($$)."_"; $queryid .= time."_"; $queryid .= $run; print $client "$queryid\n"; #prepare and execute the query my $sth = $dbh->prepare($query); my $result; unless ($sth->execute()) { &logthis("WARNING: Could not retrieve from database: $@"); $result=""; } else { my $r1=$sth->fetchall_arrayref; my @r2; map {my $a=$_; my @b=map {escape($_)} @$a; push @r2,join(",", @b)} (@$r1); $result=join("&",@r2) . "\n"; } &reply("queryreply:$queryid:$result",$conserver); } # tidy up gracefully and finish #close the database handle $dbh->disconnect or &logthis("WARNING: Couldn't disconnect from database $DBI::errstr ($st secs): $@"); # this exit is VERY important, otherwise the child will become # a producer of more and more children, forking yourself into # process death. exit; } } ** LOND enabling of MySQL requestsw This code is part of every lond child process in the way that it parses command request syntax sent to it from lonc processes. querysend corresponds to B-lonc sending the result of the query. queryreply corresponds to B-lond indicating that it has received the request and will start the database transaction (it returns "ok" to A-lonc ($client)). # ------------------------------------------------------------------- querysend } elsif ($userinput =~ /^querysend/) { my ($cmd,$query)=split(/:/,$userinput); $query=~s/\n*$//g; print $client sqlreply("$hostid{$clientip}\&$query")."\n"; # ------------------------------------------------------------------ queryreply } elsif ($userinput =~ /^queryreply/) { my ($cmd,$id,$reply)=split(/:/,$userinput); my $store; my $execdir=$perlvar{'lonDaemons'}; if ($store=IO::File->new(">$execdir/tmp/$id")) { print $store $reply; close $store; print $client "ok\n"; } else { print $client "error:$!\n"; } ** TEST the database connection with my current tester.pl code which mimics what command will eventually be sent through lonc. $reply=reply( "querysend:SELECT * FROM general_information WHERE Id='AAAAA'",$lonID);