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List:       dbi-dev
Subject:    Re: DBD naming question?
From:       Tim Bunce <Tim.Bunce () pobox ! com>
Date:       2002-01-29 12:02:22
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On Mon, Jan 28, 2002 at 05:14:07PM -0800, Schuyler Erle wrote:
> Tim Bunce wrote:
> > 
> > On Wed, Jan 23, 2002 at 04:34:03PM -0800, Schuyler Erle wrote:
> > > Hello. I've written a DBD module to wrap other DBD handles and provide
> > > intelligent drop-in support for asymmetrically replicated databases
> > > (e.g., MySQL v3)... [snip] Suggestions?
> > 
> > Is it not possible to implement the functionality you need by using
> > (or extending) DBD::Multiplex?
> > 
> > http://www.cpan.org/modules/by-authors/id/T/TK/TKISHEL/Multiplex-1.6.pm
> > 
> > It's exactly the kind of application that DBD::Multiplex exists for
> > and if DBD::Multiplex can't support it now then it needs to be
> > fixed/extended so it can. Edwin Pratomo recently contributed
> > some master/slave logic that may already do exactly want you need.
> 
> Thanks, Tim. I was in fact able to get DBD::Multiplex to work
> brilliantly with our application.

Great.

> I ran into two problems, which I would be happy to help resolve.
> 
> First, DBD::Multiplex doesn't ship as a perl module distribution. This
> makes it impossible to find or install using the usual CPAN utilities
> (e.g. search.cpan.org, CPAN.pm, etc.) ... If Thomas would like
> assistance whipping this into a distributable tarball, I'll be honored
> to help.

I hope he will. (I messed upo his email originally but I've fixed
it in this email, so hopefully he'll reply.)

Tim.

> Second, Apache::DBI does the Wrong Thing with DBD::Multiplex, since
> DBD::Multiplex always calls DBI->connect() on its subhandles with nested
> hashes in the attribute hash. Apache::DBI 1.88 just stringifies these
> hashrefs, meaning that it comes up with a different value on effectively
> *every* call to connect(). This is definitely a deficiency in
> Apache::DBI, so I've cc'd Edmund Mergl and included a full patch at the
> end of this e-mail. Edmund -- if you could review my patch, and let me
> know whether you'll accept it, and how soon we might expect a new
> release of Apache::DBI, I would *really* appreciate it. I'm definitely
> open to tinkering with the patch to make it suit your needs and
> preferences.
> 
> I'd really like to see these two issues resolved as soon as possible,
> and I put myself at your respective disposals towards sorting them out.
> Thanks very much to everyone involved for your code and your time.
> 
> SDE
> 
> --- DBI.pm	Fri Jan 12 10:59:00 2001
> +++ DBI.pm.new	Mon Jan 28 13:25:31 2002
> @@ -23,6 +23,45 @@
>  my %LastPingTime; # keeps track of last ping per data_source
>  my $Idx;          # key of %Connected and %Rollback.
>  
> +# Auxilliary code to serialize arguments to connect(). 
> +
> +my @serializers = (
> +    Storable       => "freeze",
> +    FreezeThaw	    => "freeze",
> +    "Data::Denter" => "Indent",
> +    "Data::Dumper" => "Dumper"
> +);
> +
> +my $serialize;
> +
> +sub _load_serializer {
> +    my @modules = @serializers;
> +    while ( @modules and not $serialize ) {
> +	my ($pkg, $method) = splice(@modules, 0, 2);
> +	next unless eval "require $pkg";
> +	$serialize = $pkg->can( $method );
> +    }
> +    $serialize = 0 unless ref $serialize; # Don't try again next time.
> +    return $serialize;
> +}
> +
> +sub _serialize {
> +    _load_serializer() unless defined $serialize;
> +    if ( ref $serialize ) {
> +	return $serialize->( @_ );
> +    } else {
> +	require Carp;
> +    	Carp::carp "References in attribute hash not serialized properly
> ",
> +    	    "by Apache::DBI (i.e., you should install Storable or ",
> +    	    "Data::Denter)";
> +    	return _stringify_hash( @_ );
> +    }
> +}
> +
> +sub _stringify_hash {
> +    my $hash = shift;
> +    return join($;, map( "$_=$hash->{$_}", keys %$hash ));
> +}
>  
>  # supposed to be called in a startup script.
>  # stores the data_source of all connections, which are supposed to be
> created upon
> @@ -68,11 +106,15 @@
>  
>      # the hash-reference differs between calls even in the same
>      # process, so de-reference the hash-reference 
> +    #
> +    # Do a full serialization if there are references in the hash.
> +    # Otherwise, just stringify the thing.
>      if (3 == $#args and ref $args[3] eq "HASH") {
> -       my ($key, $val);
> -       while (($key,$val) = each %{$args[3]}) {
> -           $Idx .= "$;$key=$val";
> -       }
> +	if (grep( ref $_, values %{$args[3]} )) {
> +	    $Idx .= $; . _serialize( $args[3] );
> +	} else {
> +	    $Idx .= $; . _stringify_hash( $args[3] );
> +	}
>      } elsif (3 == $#args) {
>          pop @args;
>      }
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