Package com.github.benmanes.caffeine.cache.simulator.policy.two_queue

Class TuQueuePolicy

  • All Implemented Interfaces:
    Policy, Policy.KeyOnlyPolicy
    public class TuQueuePolicy
extends Object
implements Policy.KeyOnlyPolicy
    An adaption of the 2Q algorithm used by OpenBSD and memcached. Unlike the original 2Q algorithm, non-resident entries are not retained in the TU-Q policy. For details see OpenBSD description at 2Q buffer cache algorithm and memcached's at [Work In Progress] LRU rework.

    "We retain the key three working set distinction. In the OpenBSD code, they are named hot, cold, and warm, and each is an LRU queue. New buffers start hot. They stay that way as long as they remain on the hot queue. Eventually, a buffer will slip from the end of the hot queue onto the front of the cold queue. (We preserve the data, not just the address.) When a new buffer is needed, we recycle one from the tail of the cold queue. The oldest and coldest. If, on the other hand, we have a cache hit on a cold buffer, it turns into a warm buffer and goes to the front of the warm queue. Then as the warm queue lengthens, buffers start slipping from the end onto the cold queue. Both the hot and warm queues are capped at one third of memory each to ensure balance.

    Scan resistance is achieved by means of the warm queue. Transient data will pass from hot queue to cold queue and be recycled. Responsiveness is maintained by making the warm queue LRU so that expired long term set buffers fade away."

    • Constructor Detail

      • TuQueuePolicy

        public TuQueuePolicy​(Config config)

    • Method Detail

      • stats

        public PolicyStats stats()
        Description copied from interface: Policy
        Returns the cache efficiency statistics.
        Specified by:
        stats in interface Policy

      • finished

        public void finished()
        Description copied from interface: Policy
        Indicates that the recording has completed.
        Specified by:
        finished in interface Policy