Author image Tomás Cohen Arazi
and 1 contributors


Memoize::Memcached - use a memcached cache to memoize functions


    use Memoize::Memcached
      memcached => {
        servers => [ '' ],


    # Function 'foo' is now memoized using the memcached server
    # running on as the cache.


The way flush_cache works with memcached can be dangerous. Please read the documentation below on flush_cache.


This module exports memoize_memcached, flush_cache, and unmemoize. The unmemoize function is just the one from Memoize, and is made available for convenience.



This is the memcached equivalent of memoize. It works very similarly, except for some difference in options.

If the LIST_CACHE or SCALAR_CACHE options are passed in, memoize_memcached will complain and then pass the request along to memoize. The result will be a memoized function, but using whatever cache you specified and NOT using memcached at all.

This function also accepts a memcached option, which expects a hashref. This is de-referenced and passed directly into an internal function which sets up the memcached configuration for that function. This contents of this hashref are mostly options passed to Cache::Memcached, with a few exceptions.

The actual key used to look up memoize data in memcached is formed from the function name, the normalized arguments, and some additional prefixes which can be set via the memcached option. These prefixes are key_prefix, list_key_prefix, and scalar_key_prefix.

The key_prefix defaults to "memoize-" if it's not passed in, or an undefined value is passed in.

The list_key_prefix and scalar_key_prefix options default to "list-" and "scalar-" respectively, by the same criteria.

So, the default way the key is generated is:

  "memoize-<function>-list-<normalized args>"


  "memoize-<function>-scalar-<normalized args>"

The function and normalized args portion of this key are set internally, but the "memoize-" prefix and the context portion can be configured with memcached options as follows:




  # keys generated will look like this:
  #  list context:   memoize-foo-list-<argument signature>
  #  scalar context: memoize-foo-scalar-<argument signature>

    memcached => {
      servers => [ ... ],
      key_prefix        => '_M-',
      list_key_prefix   => 'L-',
      scalar_key_prefix => 'S-',

  # keys generated will look like this:
  #  list context:   _M-foo-L-<argument signature>
  #  scalar context: _M-foo-S-<argument signature>


The behavior documented in Memoize is sort of implemented. A call to flush_cache('memoized_function') will indeed clear the cache of all cached return values for that function, BUT it will also clear the entire memcached cache, including all other memoized functions using the same memcached cache, and even data unrelated to Memoize::Memcached in the same cache. It will flush the entire cache.

There are 2 new ways to call this function:



    flush_cache(memoized_function => qw( an argument signature ));

The call without arguments will flush the entire memcached cache, just like the 1 argument version. This includes unrelated data. Be careful.

The call with 2 or more arguments will flush only the cached return values (array and scalar contexts) for a call to the function named by the first argument with an argument signature matching the second argument to the end. Unlike the other 2 ways to call this function, when called this way only the specified part of the cache is flushed.

I would recommended that only the 2 or more argument version of flush_cache be called unless you are very sure of what you are doing.


The biggest gotcha is that you probably never want to call flush_cache('memoized_function'). Because of the way CLEAR is implemented against memcached, this call will flush the entire memcached cache. Everything. Even stuff having nothing to do with Memoize::Memcached. You are warned.


A more intuitive interface for handling different memcached server configurations would probably be useful.


David Trischuk, <trischuk at>


Please report any bugs or feature requests to bug-memoize-memcached at, or through the web interface at I will be notified, and then you'll automatically be notified of progress on your bug as I make changes.


You can find documentation for this module with the perldoc command.

    perldoc Memoize::Memcached

You can also look for information at:


The tied hash portion of this module is heavily based on Cache::Memcached::Tie by Andrew Kostenko.


Copyright 2008 David Trischuk, all rights reserved.

This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.