A general caveat is that using this adapter reserves any cache key starting
with '__tag.'.
Using the same pool is precarious if your cache does LRU evictions of items
even if they do not expire (as in e.g. memcached). If so, the tag item may
be evicted without all of the tagged items having been evicted first,
causing items to lose their tags.
In order to mitigate this issue, you may use a separate, more persistent
pool for your tag items. Do however note that if you are doing so, the
entire pool is reserved for tags, as this pool is cleared whenever the
main pool is cleared.