mod_perl memory question

[avo]

Hi, I have being designing a module in Perl which is using a private hash to store some data when certain method is called. It looks like this:

package sharedcache;

use strict;
my $cache;

sub store {
  $cache .= $_[0];
}

sub get {
  return $cache;
}

1;

In mod_perl environment the data stored in $cache doesn't die after execution of the mod_perl script. The data stays in $cache until a web server restart. The issue I have is that because Apache forks couple of processes each process carry its own copy of this module and $cache. I need fast temporary storage for better response time towards the client. In my application I store the data in $cache until certain moment when the client confirms the data, when I store it in MySQL table. I also tried using tied db like this:

tie %tempdb, 'SDBM_File', $databasefile, O_CREAT|O_RDWR, 0644;

Which had exactly the same issue - each apache process kept its own copy of it. Is there a better way to do that. Thanks.

[moritz]

I'd suggest memcached and one of its perl bindings.

[perrin]

Both MySQL and SDBM_File should work fine for this. MySQL is very fast at this kind of simple data access. If you'd rather use a dbm file, try using SDBM_File through the MLDBM::Sync module, which handles the locking.

If this is really a cache, not a database, and you don't care if you might lose the data, then memcached is ok too, but if you only have one machine (not a cluster) and don't mind the possibility of data loss, Cache::FastMmap is the fastest thing around.

You might also look at CHI for a high-level interface that lets you try various caching modules.

[Rhandom]

If the cache needs to be shared among children - I second the vote for memcache.

If each child needs its own, I'd do something like the following using the End module:



# add clear_cache method to your sharedcache
package sharedcache;
sub clear_cache { $cache = undef }


# inside your apache handler use the following:

use End;
sub handler {
    my $clear_cache = end { sharedcache::clear_cache() };

    # normal handler operations go here
}



When your handler goes out of scope - the object stored in $clear_cache will go out of scope and the stored coderef will fire - clearing your cache.