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Re: Re: mysql, locked databases, Apache::DBI and mod_perl

by Flame (Deacon)
on May 20, 2003 at 03:39 UTC ( #259353=note: print w/ replies, xml ) Need Help??


in reply to Re: mysql, locked databases, Apache::DBI and mod_perl
in thread mysql, locked databases, Apache::DBI and mod_perl

Ok, I've managed to narrow it down using a series of warn() statements represented by &pdebugger; in the following code, in combination with -X. From the top of the file, to where the problem occurs, and a little more:

#!/usr/bin/perl use DBI; use Date::Calc qw(Days_in_Month Day_of_Week Today Decode_Day_of_Week T +his_Year check_date Day_of_Year Delta_Days Month_to_Text); use CGI::Util qw(escape); use HTML::Entities qw(encode_entities); use Data::Dumper; use Digest::MD5 'md5_base64'; use Data::Page; #To simplify paging logic use HTML::CalendarMonthSimple; use Apache::Request; use Apache::Cookie; use Tie::IxHash; use Apache::Session::MySQL; #use Date::Format; use Parse::RecDescent; #use IO::File; use strict; #This can be declared here because it never changes our %months; tie(%months,'Tie::IxHash'); %months = qw(9 September 10 October 11 November 12 December 1 January +2 February 3 March 4 April 5 May 6 June); #Filters for fields used in each mode TO BE REDONE our @newfields = ('type','title',qr/^new\d+(?:day|month)$/,qr/^[se]t\d ++(?:-\d+)?$/,qr/^newtype\d+(?:-\d+)?$/,'newspec',qr/^keepday\d+$/,qr/ +^desc\d+(?:-\d+)?$/,'expire',qr/^apm[se]\d+(?:-\d+)?$/,qr/codeblock\d ++/,'cmd','fields',qr/^newexp(?:day|month$)/); our @browsefields = ('cid'); our $timeparse = qr/^0?([12]?\d):(\d+):00$/; #Initialize the state, this will be passed to all subs my $state = {}; &pdebugger; #Scope all processing that sets variables { #Get the Apache::Request object my $r = new Apache::Request(shift); my $cookie = new Apache::Cookie($r, -name => 'MY_SESSION_ID', -path => '/', ); my %cookies = $cookie->parse; my $DBH = DBI->connect('dbi:mysql:schedule;host=localhost','root',' +',{RaiseError => 1}); &pdebugger; { #Used to demonstrate that mysql itself can still communicate my $sth = $DBH->prepare("SELECT * from users"); $sth->execute; warn(Dumper($sth->fetchall_arrayref)); } #Session code adapted from: # Apache::Session docs # HTML::Mason samples # code available at http://www.masonhq.com/user/adpacifico/Apache +SessionMason.html my %session; &pdebugger; eval { tie %session, 'Apache::Session::MySQL', ($cookies{'MY_SESSION_ID'} ? $cookies{'MY_SESSION_ID'}->value +() : undef), { Handle => $DBH, LockHandle => $DBH }; }; &pdebugger; # If we could not re-establish an existing, $@ should contain # 'Object does not exist in the data store'. If the eval # failed for a different reason, that might be important if ($@) { if ($@ =~ m#^Object does not exist in the data store#) { #this will create a new session entry tie %session, 'Apache::Session::MySQL', undef, { Handle => $DBH, LockHandle => $DBH }; undef $cookies{'MY_SESSION_ID'}; } else { #place message in server log warn $@; } } &pdebugger; $cookie->value( $session{'_session_id'} ); $cookie->bake; #Add to header queue &pdebugger; $r->send_http_header('text/html'); &pdebugger; # Timestamp the session hash to ensure Apache::Session writes # out the data store The reason for this is that # Apache::Session only does a shallow check for changes in # %session. If %session contains references to objects whose # attributes have changed, those changes won't be recorded. So # adding a 'timestamp' key with a value that changes every # request ensures that all data structures are stored to disk. $session{'timestamp'}=localtime; #End session establishing code #End localization block, place everything needed into the state #Prepare to release tables later #$state->{'ulock'} = $DBH->prepare('UNLOCK TABLES'); $state->{'r'} = $r; $state->{'session'} = \%session; $state->{'DBH'} = $DBH; } &pdebugger;

The first time through, everything runs fine, however, on the second attempt, things go wrong. I've traced it down to the first session declarations, repeated here:

#Session code adapted from: # Apache::Session docs # HTML::Mason samples # code available at http://www.masonhq.com/user/adpacifico/Apache +SessionMason.html my %session; &pdebugger; eval { tie %session, 'Apache::Session::MySQL', ($cookies{'MY_SESSION_ID'} ? $cookies{'MY_SESSION_ID'}->value +() : undef), { Handle => $DBH, LockHandle => $DBH }; }; &pdebugger;

The first &pdebugger; in this section is on line 64, the last one to print on the second run (reliably gets this far and no farther). I've concluded the problem must lie in Apache::Session somewhere, but I am at a loss to even guess where aside from the unique id generating methods or their locking mechanism. I'm not quite sure what I should attempt at this point, should I edit the actual files and see if I can find the problem, or is the problem in my use of Apache::Session? Well... at least I'm gaining some ground.



My code doesn't have bugs, it just develops random features.

Flame ~ Lead Programmer: GMS (DOWN) | GMS (DOWN)


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Re: Re: Re: mysql, locked databases, Apache::DBI and mod_perl
by perrin (Chancellor) on May 20, 2003 at 18:19 UTC
    Can you give more explanation of "things go wrong"? What happens, exactly? Does it hang? Do you get error messages?
      As I said before, it just stops, like it got itself stuck in a loop.



      My code doesn't have bugs, it just develops random features.

      Flame ~ Lead Programmer: GMS (DOWN) | GMS (DOWN)

        Sounds like you are having problems with Apache::Session's locking system because the session object isn't being destroyed at the end of a request in some situation. It could be that you accidentally made a closure somewhere that holds the %state hash.

        The shotgun solution is to simply stop using Apache::Session's locking. Change from Apache::Session::MySQL to Apache::Session::Flex or just change Apache::Session::MySQL itself and use the NullLocker instead of the MySQL locker. However, that might mask the larger problem which is that your session data doesn't get saved when the object doesn't get destroyed.

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