guava-cached-store.clj

(ns yeller.store.guava-cached-store
  (:require [metrics.counters :refer [counter inc!]]
            [metrics.gauges :refer [gauge]]
            [liza.store :as store])
  (:import (com.google.common.cache CacheBuilder CacheLoader
                                    LoadingCache RemovalListener)
           (java.util.concurrent TimeUnit)))

(deftype GuavaCachedBucket [original-bucket ^LoadingCache cache]
  store/Bucket
  (store/get [b k]
    (try
      (.get cache k)
      (catch com.google.common.cache.CacheLoader$InvalidCacheLoadException _
        nil)))

  (store/put [b k v]
    (store/put original-bucket k v))

  store/MergeableBucket
  (store/merge [b v1 v2]
    (store/merge original-bucket v1 v2))

  store/Wipeable
  (store/wipe [b]
    (store/wipe original-bucket)))

(defn track-cache-stats [bucket-name ^LoadingCache cache]
  (gauge ["yeller.store.guava-cached-store" bucket-name "hit-rate"]
         (.hitRate (.stats cache)))

  (gauge ["yeller.store.guava-cached-store" bucket-name "eviction-count"]
         (.evictionCount (.stats cache)))

  (gauge ["yeller.store.guava-cached-store" bucket-name "average-load-penalty"]
         (/ (.averageLoadPenalty (.stats cache)) 1000000)))

(defn guava-cached-bucket
  ([bucket-name original-bucket] (guava-cached-bucket bucket-name original-bucket {}))
  ([bucket-name original-bucket options]
  (let [removal-counter (counter ["yeller.store.guava-cached-store" "removals" bucket-name])
        cache
        (-> (CacheBuilder/newBuilder)
          (.maximumSize (:max-size options 1000))
          (.expireAfterWrite (:expire-after-write options 1000) TimeUnit/MILLISECONDS)
          (.removalListener
            (reify RemovalListener
              (onRemoval [_ _]
                (inc! removal-counter))))
          (.recordStats)
          (.build
            (proxy [CacheLoader] []
              (load [k]
                (store/get original-bucket k)))))]
    (track-cache-stats bucket-name cache)
    (GuavaCachedBucket. original-bucket cache))))