The default cache size for external_acl_type is 256*1024 not unbounded as
documentation says.
Up to the value of children-max. (default 1)
concurrency=n concurrency level per process. Only used with helpers
capable of processing more than one query at a time.
- cache=n limit the result cache size, default is unbounded.
+ cache=n limit the result cache size, default is 262144.
grace=n Percentage remaining of TTL where a refresh of a
cached entry should be initiated without needing to
wait for a new reply. (default is for no grace period)