The SizeAwareCache interface is implemented by classes that support
all of the Cache::Cache interface in addition to the limit_size and
max_size features of a size aware cache.
The default cache size limiting algorithm works by removing cache
objects in the following order until the desired limit is reached:
1) objects that have expired
2) objects that are least recently accessed
3) objects that that expire next
Attempt to resize the cache such that the total disk usage is under
the $new_size parameter. $new_size represents t size (in bytes)
that the cache should be limited to. Note that this is only a one
time adjustment. To maintain the cache size, consider using the
max_size option, although it is considered very expensive, and can
often be better achieved by peridocally calling limit_size.
If this property is set, then the cache will try not to exceed the max
size value (in bytes) specified. NOTE: This causes the size of the
cache to be checked on every set, and can be considered *very*
expensive in some implementations. A good alternative approach is
leave max_size as $NO_MAX_SIZE and to periodically limit the size of
the cache by calling the limit_size( $size ) method.