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lib/Cache/Cascade.pm  view on Meta::CPAN

In a multiprocess, and especially a multiserver application caching is a very
effective means of improving results.

The tradeoff of increasing the scale of the caching is in added complexity.
For example, caching in a FastMmap based storage is much slower than using a
memory based cache, because pages must be locked to ensure that no corruption
will happen. Likewise Memcached is even more overhead than FastMmap because it
is network bound, and uses blocking IO (on the client side).

This module attempts to make a transparent cascade of caches using several
backends.

The idea is to search from the cheapest backend to the most expensive, and
depending on the options also cache results in the cheaper backends.

The benefits of using a cascade are that if the chance of a hit is much higher
in a slow cache, but checking a cheap cache is negligible in comparison, we
may already have the result we want in the cheap cache. Configure your
expiration policy so that there is approximately an order of magnitude better
probability of cache hits (bigger cache) for each level of the cascade.

=head1 FIELDS

=over 4

=item set_deep

Defaults to true. See C<set>.

=item float_hits

lib/Cache/Cascade.pm  view on Meta::CPAN

These two methods set the callback for all the caches.

=item get_and_float_result $key, @caches

This is used to implement the C<float_hits> behavior of C<get> recursively.

=back

=head1 CAVEATS

When you set or remove a key from the cascade and this propagates downwards, for
example from MemoryCache to FastMmap, other cascades will not notice the change
until their own MemoryCache is expired.

Thus, if cache invalidation is important in your algorithm (data changes) do
not use a cascade. If stale hits are permitted, or the cache is for non
changing data then you should use a cascade.

=head1 SEE ALSO

L<Cache>

=head1 SUPPORT

Bugs may be submitted through L<the RT bug tracker|https://rt.cpan.org/Public/Dist/Display.html?Name=Cache-Cascade>
(or L<bug-Cache-Cascade@rt.cpan.org|mailto:bug-Cache-Cascade@rt.cpan.org>).