[Openinteract-help] Caching does not work

[Vsevolod (S. I. <si...@cs...>]

Chris,

I have tried to use caching, because otherwise the linked_to attributes 
are retrieved anew every time, making any kind of change to them 
non-permanent. However, it does not work. I was only able to get it to 
work by overriding use_cache() and returning 1 in my SPOPS superclass.

Here's what happens:

The first time a DB call happens, SPOPS tries to get the data from the 
global cache. Irregardless of whether it was found or not, skip_cache is 
incremented:

DBI.pm

<pre>
sub fetch
{
..
if ( ref $p->{data} eq 'HASH' ) {
         $obj = $class->new({ %{ $p->{data} }, skip_default_values => 1 });
     }
     else {
         $obj = $class->get_cached_object({ %{ $p }, id => $id });
         $p->{skip_cache}++;         # Set so we don't re-cache it later
     }
..
$obj->_fetch_post_process($p, $level);
}
</pre>

Note that the last thing in the fetch() function is a call to 
_fetch_post_process in SPOPS.pm:

<pre>
sub _fetch_post_process {
     my ( $self, $p, $level ) = @_;

     # Create an entry for this object in the cache unless either the
     # class or this call to fetch() doesn't want us to.

     $self->set_cached_object( $p );
</pre>


_fetch_post_process calls set_cached_object() in SPOPS.pm. Note that 
this will fail if use_cache() returns 1;

<pre>

sub set_cached_object {
     my ( $self, $p ) = @_;
     return undef unless ( ref $self );
     return undef unless ( $self->id );
     return undef unless ( $self->use_cache( $p ) );
     return $self->global_cache->set({ data => $self });
}

</pre>

Finally, use_cache() is:

<pre>
sub use_cache {
     return undef unless ( $USE_CACHE );
     my ( $class, $p ) = @_;
     return undef if ( $p->{skip_cache} );
     return undef if ( $class->no_cache );
     return undef unless ( $class->global_cache );
     return 1;
}
</pre>

We check $p->{skip_cache}, which was set to 1 after an unsuccessful call 
to get(), return undef from use_cache()... and never call cache::set()!

I think the fix is simple - you should increment skip_cache after get() 
in fetch() only if
   ( ref $obj eq $class )

You use the same check literally one line below in determining whether 
or not to access the database.

Simon

-- 

Simon (Vsevolod ILyushchenko)   si...@cs...
				http://www.simonf.com

America's business leaders simply don't want to think
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			Andrew Grygus, www.aaxnet.com