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From a.@apache.org
Subject [lucene-solr] branch master updated: SOLR-8241: Add CaffeineCache, an efficient implementation of SolrCache.
Date Thu, 03 Oct 2019 13:17:29 GMT
This is an automated email from the ASF dual-hosted git repository.

ab pushed a commit to branch master
in repository https://gitbox.apache.org/repos/asf/lucene-solr.git


The following commit(s) were added to refs/heads/master by this push:
     new 8007ac0  SOLR-8241: Add CaffeineCache, an efficient implementation of SolrCache.
8007ac0 is described below

commit 8007ac0cb0c88838ba6e58e56e2bc23374c15dc4
Author: Andrzej Bialecki <ab@apache.org>
AuthorDate: Thu Oct 3 14:19:59 2019 +0200

    SOLR-8241: Add CaffeineCache, an efficient implementation of SolrCache.
---
 lucene/ivy-versions.properties                     |   2 +-
 solr/CHANGES.txt                                   |   2 +
 .../java/org/apache/solr/search/CaffeineCache.java | 365 +++++++++++++++++++++
 .../java/org/apache/solr/search/FastLRUCache.java  |   3 -
 .../src/java/org/apache/solr/search/SolrCache.java |   3 +
 .../org/apache/solr/util/ConcurrentLFUCache.java   | 119 +++----
 .../org/apache/solr/util/ConcurrentLRUCache.java   |  63 ++--
 .../org/apache/solr/search/TestCaffeineCache.java  | 285 ++++++++++++++++
 .../org/apache/solr/search/TestFastLRUCache.java   |  88 +++--
 .../solr/store/blockcache/BlockCacheTest.java      |  85 ++---
 solr/licenses/caffeine-2.4.0.jar.sha1              |   1 -
 solr/licenses/caffeine-2.8.0.jar.sha1              |   1 +
 .../src/query-settings-in-solrconfig.adoc          |  11 +-
 13 files changed, 870 insertions(+), 158 deletions(-)

diff --git a/lucene/ivy-versions.properties b/lucene/ivy-versions.properties
index 12f7bc8..24366c3 100644
--- a/lucene/ivy-versions.properties
+++ b/lucene/ivy-versions.properties
@@ -23,7 +23,7 @@ com.fasterxml.jackson.core.version = 2.9.9
 /com.fasterxml.jackson.core/jackson-databind = 2.9.9.3
 /com.fasterxml.jackson.dataformat/jackson-dataformat-smile = ${com.fasterxml.jackson.core.version}
 
-/com.github.ben-manes.caffeine/caffeine = 2.4.0
+/com.github.ben-manes.caffeine/caffeine = 2.8.0
 /com.github.virtuald/curvesapi = 1.04
 
 /com.google.guava/guava = 25.1-jre
diff --git a/solr/CHANGES.txt b/solr/CHANGES.txt
index d6dd837..21adf2a 100644
--- a/solr/CHANGES.txt
+++ b/solr/CHANGES.txt
@@ -152,6 +152,8 @@ New Features
 
 * SOLR-13625: Add CsvStream, TsvStream Streaming Expressions and supporting Stream Evaluators (Joel bernstein)
 
+* SOLR-8241: Add CaffeineCache, an efficient implementation of SolrCache.(Ben Manes, Shawn Heisey, David Smiley, Andrzej Bialecki)
+
 Improvements
 ----------------------
 
diff --git a/solr/core/src/java/org/apache/solr/search/CaffeineCache.java b/solr/core/src/java/org/apache/solr/search/CaffeineCache.java
new file mode 100644
index 0000000..ad4571d
--- /dev/null
+++ b/solr/core/src/java/org/apache/solr/search/CaffeineCache.java
@@ -0,0 +1,365 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.solr.search;
+
+import java.lang.invoke.MethodHandles;
+import java.time.Duration;
+import java.util.Collections;
+import java.util.Locale;
+import java.util.Map;
+import java.util.Map.Entry;
+import java.util.Optional;
+import java.util.Set;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.Executor;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.ForkJoinPool;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.LongAdder;
+
+import com.codahale.metrics.MetricRegistry;
+import com.github.benmanes.caffeine.cache.RemovalCause;
+import com.github.benmanes.caffeine.cache.RemovalListener;
+import org.apache.lucene.util.Accountable;
+import org.apache.lucene.util.RamUsageEstimator;
+import org.apache.solr.common.SolrException;
+import org.apache.solr.metrics.MetricsMap;
+import org.apache.solr.metrics.SolrMetricManager;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import com.github.benmanes.caffeine.cache.Cache;
+import com.github.benmanes.caffeine.cache.Caffeine;
+import com.github.benmanes.caffeine.cache.Policy.Eviction;
+import com.github.benmanes.caffeine.cache.stats.CacheStats;
+import com.google.common.annotations.VisibleForTesting;
+
+/**
+ * A SolrCache backed by the Caffeine caching library [1]. By default it uses the Window TinyLFU (W-TinyLFU)
+ * eviction policy.
+ * <p>This cache supports either maximum size limit (the number of items) or maximum ram bytes limit, but
+ * not both. If both values are set then only maxRamMB limit is used and maximum size limit is ignored.</p>
+ * <p>
+ * W-TinyLFU [2] is a near optimal policy that uses recency and frequency to determine which entry
+ * to evict in O(1) time. The estimated frequency is retained in a Count-Min Sketch and entries
+ * reside on LRU priority queues [3]. By capturing the historic frequency of an entry, the cache is
+ * able to outperform classic policies like LRU and LFU, as well as modern policies like ARC and
+ * LIRS. This policy performed particularly well in search workloads.
+ * <p>
+ * [1] https://github.com/ben-manes/caffeine
+ * [2] http://arxiv.org/pdf/1512.00727.pdf
+ * [3] http://highscalability.com/blog/2016/1/25/design-of-a-modern-cache.html
+ */
+public class CaffeineCache<K, V> extends SolrCacheBase implements SolrCache<K, V>, Accountable, RemovalListener<K, V> {
+  private static final Logger log = LoggerFactory.getLogger(MethodHandles.lookup().lookupClass());
+
+  private static final long BASE_RAM_BYTES_USED = RamUsageEstimator.shallowSizeOfInstance(CaffeineCache.class)
+      + RamUsageEstimator.shallowSizeOfInstance(CacheStats.class)
+      + 2 * RamUsageEstimator.shallowSizeOfInstance(LongAdder.class);
+
+  private Executor executor;
+
+  private CacheStats priorStats;
+  private long priorInserts;
+
+  private String description;
+  private LongAdder inserts;
+  private Cache<K,V> cache;
+  private long warmupTime;
+  private int maxSize;
+  private long maxRamBytes;
+  private int initialSize;
+  private int maxIdleTimeSec;
+  private boolean cleanupThread;
+
+  private Set<String> metricNames = ConcurrentHashMap.newKeySet();
+  private MetricsMap cacheMap;
+  private MetricRegistry registry;
+
+  private long initialRamBytes = 0;
+  private final LongAdder ramBytes = new LongAdder();
+
+  public CaffeineCache() {
+    this.priorStats = CacheStats.empty();
+  }
+
+  @Override
+  @SuppressWarnings({"unchecked", "rawtypes"})
+  public Object init(Map args, Object persistence, CacheRegenerator regenerator) {
+    super.init(args, regenerator);
+    String str = (String) args.get(SIZE_PARAM);
+    maxSize = (str == null) ? 1024 : Integer.parseInt(str);
+    str = (String) args.get("initialSize");
+    initialSize = Math.min((str == null) ? 1024 : Integer.parseInt(str), maxSize);
+    str = (String) args.get(MAX_IDLE_TIME_PARAM);
+    if (str == null) {
+      maxIdleTimeSec = -1;
+    } else {
+      maxIdleTimeSec = Integer.parseInt(str);
+    }
+    str = (String) args.get(MAX_RAM_MB_PARAM);
+    int maxRamMB = str == null ? -1 : Double.valueOf(str).intValue();
+    maxRamBytes = maxRamMB < 0 ? Long.MAX_VALUE : maxRamMB * 1024L * 1024L;
+    str = (String) args.get(CLEANUP_THREAD_PARAM);
+    cleanupThread = str != null && Boolean.parseBoolean(str);
+    if (cleanupThread) {
+      executor = ForkJoinPool.commonPool();
+    } else {
+      executor = Runnable::run;
+    }
+
+    description = generateDescription(maxSize, initialSize);
+
+    cache = buildCache(null);
+    inserts = new LongAdder();
+
+    initialRamBytes =
+        RamUsageEstimator.shallowSizeOfInstance(cache.getClass()) +
+        RamUsageEstimator.shallowSizeOfInstance(executor.getClass()) +
+        RamUsageEstimator.sizeOfObject(description);
+
+    return persistence;
+  }
+
+  private Cache<K, V> buildCache(Cache<K, V> prev) {
+    Caffeine builder = Caffeine.newBuilder()
+        .initialCapacity(initialSize)
+        .executor(executor)
+        .removalListener(this)
+        .recordStats();
+    if (maxIdleTimeSec > 0) {
+      builder.expireAfterAccess(Duration.ofSeconds(maxIdleTimeSec));
+    }
+    if (maxRamBytes != Long.MAX_VALUE) {
+      builder.maximumWeight(maxRamBytes);
+      builder.weigher((k, v) -> (int) (RamUsageEstimator.sizeOfObject(k) + RamUsageEstimator.sizeOfObject(v)));
+    } else {
+      builder.maximumSize(maxSize);
+    }
+    Cache<K, V> newCache = builder.build();
+    if (prev != null) {
+      newCache.putAll(prev.asMap());
+    }
+    return newCache;
+  }
+
+  @Override
+  public void onRemoval(K key, V value, RemovalCause cause) {
+    ramBytes.add(
+        - (RamUsageEstimator.sizeOfObject(key, RamUsageEstimator.QUERY_DEFAULT_RAM_BYTES_USED) +
+        RamUsageEstimator.sizeOfObject(value, RamUsageEstimator.QUERY_DEFAULT_RAM_BYTES_USED) +
+        RamUsageEstimator.LINKED_HASHTABLE_RAM_BYTES_PER_ENTRY)
+    );
+  }
+
+  @Override
+  public long ramBytesUsed() {
+    return BASE_RAM_BYTES_USED + initialRamBytes + ramBytes.sum();
+  }
+
+  @Override
+  public V get(K key) {
+    return cache.getIfPresent(key);
+  }
+
+  @Override
+  public V put(K key, V val) {
+    inserts.increment();
+    V old = cache.asMap().put(key, val);
+    ramBytes.add(RamUsageEstimator.sizeOfObject(key, RamUsageEstimator.QUERY_DEFAULT_RAM_BYTES_USED) +
+        RamUsageEstimator.sizeOfObject(val, RamUsageEstimator.QUERY_DEFAULT_RAM_BYTES_USED));
+    if (old != null) {
+      ramBytes.add(- RamUsageEstimator.sizeOfObject(old, RamUsageEstimator.QUERY_DEFAULT_RAM_BYTES_USED));
+    } else {
+      ramBytes.add(RamUsageEstimator.LINKED_HASHTABLE_RAM_BYTES_PER_ENTRY);
+    }
+    return old;
+  }
+
+  @Override
+  public void clear() {
+    cache.invalidateAll();
+    ramBytes.reset();
+  }
+
+  @Override
+  public int size() {
+    return cache.asMap().size();
+  }
+
+  @Override
+  public void close() {
+    cache.invalidateAll();
+    cache.cleanUp();
+    if (executor instanceof ExecutorService) {
+      ((ExecutorService)executor).shutdownNow();
+    }
+    ramBytes.reset();
+  }
+
+  @Override
+  public int getMaxSize() {
+    return maxSize;
+  }
+
+  @Override
+  public void setMaxSize(int maxSize) {
+    if (this.maxSize == maxSize) {
+      return;
+    }
+    Optional<Eviction<K, V>> evictionOpt = cache.policy().eviction();
+    if (evictionOpt.isPresent()) {
+      Eviction<K, V> eviction = evictionOpt.get();
+      eviction.setMaximum(maxSize);
+      this.maxSize = maxSize;
+      initialSize = Math.min(1024, this.maxSize);
+      description = generateDescription(this.maxSize, initialSize);
+      cache.cleanUp();
+    }
+  }
+
+  @Override
+  public int getMaxRamMB() {
+    return maxRamBytes != Long.MAX_VALUE ? (int) (maxRamBytes / 1024L / 1024L) : -1;
+  }
+
+  @Override
+  public void setMaxRamMB(int maxRamMB) {
+    long newMaxRamBytes = maxRamMB < 0 ? Long.MAX_VALUE : maxRamMB * 1024L * 1024L;
+    if (newMaxRamBytes != maxRamBytes) {
+      maxRamBytes = newMaxRamBytes;
+      Optional<Eviction<K, V>> evictionOpt = cache.policy().eviction();
+      if (evictionOpt.isPresent()) {
+        Eviction<K, V> eviction = evictionOpt.get();
+        if (!eviction.isWeighted()) {
+          // rebuild cache using weigher
+          cache = buildCache(cache);
+          return;
+        } else if (maxRamBytes == Long.MAX_VALUE) {
+          // rebuild cache using maxSize
+          cache = buildCache(cache);
+          return;
+        }
+        eviction.setMaximum(newMaxRamBytes);
+        description = generateDescription(this.maxSize, initialSize);
+        cache.cleanUp();
+      }
+    }
+  }
+
+  @Override
+  public void warm(SolrIndexSearcher searcher, SolrCache<K,V> old) {
+    if (regenerator == null) {
+      return;
+    }
+    
+    long warmingStartTime = System.nanoTime();
+    Map<K, V> hottest = Collections.emptyMap();
+    CaffeineCache<K,V> other = (CaffeineCache<K,V>)old;
+
+    // warm entries
+    if (isAutowarmingOn()) {
+      Eviction<K, V> policy = other.cache.policy().eviction().get();
+      int size = autowarm.getWarmCount(other.cache.asMap().size());
+      hottest = policy.hottest(size);
+    }
+
+    for (Entry<K, V> entry : hottest.entrySet()) {
+      try {
+        boolean continueRegen = regenerator.regenerateItem(
+            searcher, this, old, entry.getKey(), entry.getValue());
+        if (!continueRegen) {
+          break;
+        }
+      }
+      catch (Exception e) {
+        SolrException.log(log, "Error during auto-warming of key:" + entry.getKey(), e);
+      }
+    }
+
+    inserts.reset();
+    priorStats = other.cache.stats().plus(other.priorStats);
+    priorInserts = other.inserts.sum() + other.priorInserts;
+    warmupTime = TimeUnit.MILLISECONDS.convert(System.nanoTime() - warmingStartTime, TimeUnit.NANOSECONDS);
+  }
+
+  /** Returns the description of this cache. */
+  private String generateDescription(int limit, int initialSize) {
+    return String.format(Locale.ROOT, "TinyLfu Cache(maxSize=%d, initialSize=%d%s)",
+        limit, initialSize, isAutowarmingOn() ? (", " + getAutowarmDescription()) : "");
+  }
+
+  //////////////////////// SolrInfoBean methods //////////////////////
+
+  @Override
+  public String getName() {
+    return CaffeineCache.class.getName();
+  }
+
+  @Override
+  public String getDescription() {
+     return description;
+  }
+
+  // for unit tests only
+  @VisibleForTesting
+  MetricsMap getMetricsMap() {
+    return cacheMap;
+  }
+
+  @Override
+  public MetricRegistry getMetricRegistry() {
+    return registry;
+  }
+
+  @Override
+  public String toString() {
+    return name() + (cacheMap != null ? cacheMap.getValue().toString() : "");
+  }
+
+  @Override
+  public Set<String> getMetricNames() {
+    return metricNames;
+  }
+
+  @Override
+  public void initializeMetrics(SolrMetricManager manager, String registryName, String tag, String scope) {
+    registry = manager.registry(registryName);
+    cacheMap = new MetricsMap((detailed, map) -> {
+      CacheStats stats = cache.stats();
+      long insertCount = inserts.sum();
+
+      map.put(LOOKUPS_PARAM, stats.requestCount());
+      map.put(HITS_PARAM, stats.hitCount());
+      map.put(HIT_RATIO_PARAM, stats.hitRate());
+      map.put(INSERTS_PARAM, insertCount);
+      map.put(EVICTIONS_PARAM, stats.evictionCount());
+      map.put(SIZE_PARAM, cache.asMap().size());
+      map.put("warmupTime", warmupTime);
+      map.put(RAM_BYTES_USED_PARAM, ramBytesUsed());
+      map.put(MAX_RAM_MB_PARAM, getMaxRamMB());
+
+      CacheStats cumulativeStats = priorStats.plus(stats);
+      map.put("cumulative_lookups", cumulativeStats.requestCount());
+      map.put("cumulative_hits", cumulativeStats.hitCount());
+      map.put("cumulative_hitratio", cumulativeStats.hitRate());
+      map.put("cumulative_inserts", priorInserts + insertCount);
+      map.put("cumulative_evictions", cumulativeStats.evictionCount());
+    });
+    manager.registerGauge(this, registryName, cacheMap, tag, true, scope, getCategory().toString());
+  }
+}
diff --git a/solr/core/src/java/org/apache/solr/search/FastLRUCache.java b/solr/core/src/java/org/apache/solr/search/FastLRUCache.java
index 1cec0aa..6353b21 100644
--- a/solr/core/src/java/org/apache/solr/search/FastLRUCache.java
+++ b/solr/core/src/java/org/apache/solr/search/FastLRUCache.java
@@ -54,9 +54,6 @@ public class FastLRUCache<K, V> extends SolrCacheBase implements SolrCache<K, V>
 
   public static final String MIN_SIZE_PARAM = "minSize";
   public static final String ACCEPTABLE_SIZE_PARAM = "acceptableSize";
-  public static final String INITIAL_SIZE_PARAM = "initialSize";
-  public static final String CLEANUP_THREAD_PARAM = "cleanupThread";
-  public static final String SHOW_ITEMS_PARAM = "showItems";
 
   // contains the statistics objects for all open caches of the same type
   private List<ConcurrentLRUCache.Stats> statsList;
diff --git a/solr/core/src/java/org/apache/solr/search/SolrCache.java b/solr/core/src/java/org/apache/solr/search/SolrCache.java
index 9fe186a..af390a7 100644
--- a/solr/core/src/java/org/apache/solr/search/SolrCache.java
+++ b/solr/core/src/java/org/apache/solr/search/SolrCache.java
@@ -38,6 +38,9 @@ public interface SolrCache<K,V> extends SolrInfoBean, SolrMetricProducer {
   String RAM_BYTES_USED_PARAM = "ramBytesUsed";
   String MAX_RAM_MB_PARAM = "maxRamMB";
   String MAX_IDLE_TIME_PARAM = "maxIdleTime";
+  String INITIAL_SIZE_PARAM = "initialSize";
+  String CLEANUP_THREAD_PARAM = "cleanupThread";
+  String SHOW_ITEMS_PARAM = "showItems";
 
   /**
    * The initialization routine. Instance specific arguments are passed in
diff --git a/solr/core/src/java/org/apache/solr/util/ConcurrentLFUCache.java b/solr/core/src/java/org/apache/solr/util/ConcurrentLFUCache.java
index 3aca5d5..8795e33 100644
--- a/solr/core/src/java/org/apache/solr/util/ConcurrentLFUCache.java
+++ b/solr/core/src/java/org/apache/solr/util/ConcurrentLFUCache.java
@@ -23,8 +23,9 @@ import java.util.Map;
 import java.util.TreeSet;
 import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.TimeUnit;
-import java.util.concurrent.atomic.AtomicInteger;
+//import java.util.concurrent.atomic.AtomicInteger;
 import java.util.concurrent.atomic.AtomicLong;
+import java.util.concurrent.atomic.LongAdder;
 import java.util.concurrent.locks.ReentrantLock;
 
 import org.apache.lucene.util.Accountable;
@@ -69,7 +70,7 @@ public class ConcurrentLFUCache<K, V> implements Cache<K,V>, Accountable {
   private long maxIdleTimeNs;
   private final TimeSource timeSource = TimeSource.NANO_TIME;
   private final AtomicLong oldestEntry = new AtomicLong(0L);
-  private final AtomicLong ramBytes = new AtomicLong(0);
+  private final LongAdder ramBytes = new LongAdder();
 
   public ConcurrentLFUCache(int upperWaterMark, final int lowerWaterMark, int acceptableSize,
                             int initialSize, boolean runCleanupThread, boolean runNewThreadForCleanup,
@@ -155,11 +156,11 @@ public class ConcurrentLFUCache<K, V> implements Cache<K,V>, Accountable {
   public V get(K key) {
     CacheEntry<K, V> e = map.get(key);
     if (e == null) {
-      if (islive) stats.missCounter.incrementAndGet();
+      if (islive) stats.missCounter.increment();
     } else if (islive) {
       e.lastAccessed = timeSource.getEpochTimeNs();
-      stats.accessCounter.incrementAndGet();
-      e.hits.incrementAndGet();
+      stats.accessCounter.increment();
+      e.hits.increment();
     }
     return e != null ? e.value : null;
   }
@@ -168,8 +169,8 @@ public class ConcurrentLFUCache<K, V> implements Cache<K,V>, Accountable {
   public V remove(K key) {
     CacheEntry<K, V> cacheEntry = map.remove(key);
     if (cacheEntry != null) {
-      stats.size.decrementAndGet();
-      ramBytes.addAndGet(-cacheEntry.ramBytesUsed() - HASHTABLE_RAM_BYTES_PER_ENTRY);
+      stats.size.decrement();
+      ramBytes.add(-cacheEntry.ramBytesUsed() - HASHTABLE_RAM_BYTES_PER_ENTRY);
       return cacheEntry.value;
     }
     return null;
@@ -187,23 +188,24 @@ public class ConcurrentLFUCache<K, V> implements Cache<K,V>, Accountable {
    * @lucene.internal
    */
   public V putCacheEntry(CacheEntry<K, V> e) {
-    stats.accessCounter.incrementAndGet();
+    stats.accessCounter.increment();
     // initialize oldestEntry
     oldestEntry.updateAndGet(x -> x > e.lastAccessed  || x == 0 ? e.lastAccessed : x);
     CacheEntry<K, V> oldCacheEntry = map.put(e.key, e);
     int currentSize;
     if (oldCacheEntry == null) {
-      currentSize = stats.size.incrementAndGet();
-      ramBytes.addAndGet(e.ramBytesUsed() + HASHTABLE_RAM_BYTES_PER_ENTRY); // added key + value + entry
+      stats.size.increment();
+      currentSize = stats.size.intValue();
+      ramBytes.add(e.ramBytesUsed() + HASHTABLE_RAM_BYTES_PER_ENTRY); // added key + value + entry
     } else {
-      currentSize = stats.size.get();
-      ramBytes.addAndGet(-oldCacheEntry.ramBytesUsed());
-      ramBytes.addAndGet(e.ramBytesUsed());
+      currentSize = stats.size.intValue();
+      ramBytes.add(-oldCacheEntry.ramBytesUsed());
+      ramBytes.add(e.ramBytesUsed());
     }
     if (islive) {
-      stats.putCounter.incrementAndGet();
+      stats.putCounter.increment();
     } else {
-      stats.nonLivePutCounter.incrementAndGet();
+      stats.nonLivePutCounter.increment();
     }
 
     // Check if we need to clear out old entries from the cache.
@@ -242,7 +244,7 @@ public class ConcurrentLFUCache<K, V> implements Cache<K,V>, Accountable {
       isCleaning = true;
       this.lowHitCount = lowHitCount; // volatile write to make isCleaning visible
       
-      int sz = stats.size.get();
+      int sz = stats.size.intValue();
       boolean evictByIdleTime = maxIdleTimeNs != Long.MAX_VALUE;
       long idleCutoff = evictByIdleTime ? timeSource.getEpochTimeNs() - maxIdleTimeNs : -1L;
       if (sz <= upperWaterMark && (evictByIdleTime && oldestEntry.get() > idleCutoff)) {
@@ -264,7 +266,7 @@ public class ConcurrentLFUCache<K, V> implements Cache<K,V>, Accountable {
           if (entry.getValue().lastAccessedCopy < idleCutoff) {
             iterator.remove();
             postRemoveEntry(entry.getValue());
-            stats.evictionIdleCounter.incrementAndGet();
+            stats.evictionIdleCounter.increment();
           } else {
             if (entry.getValue().lastAccessedCopy < currentOldestEntry) {
               currentOldestEntry = entry.getValue().lastAccessedCopy;
@@ -275,7 +277,7 @@ public class ConcurrentLFUCache<K, V> implements Cache<K,V>, Accountable {
           oldestEntry.set(currentOldestEntry);
         }
         // refresh size and maybe return
-        sz = stats.size.get();
+        sz = stats.size.intValue();
         if (sz <= upperWaterMark) {
           return;
         }
@@ -286,10 +288,11 @@ public class ConcurrentLFUCache<K, V> implements Cache<K,V>, Accountable {
 
       for (CacheEntry<K, V> ce : map.values()) {
         // set hitsCopy to avoid later Atomic reads.  Primitive types are faster than the atomic get().
-        ce.hitsCopy = ce.hits.get();
+        ce.hitsCopy = ce.hits.longValue();
         ce.lastAccessedCopy = ce.lastAccessed;
         if (timeDecay) {
-          ce.hits.set(ce.hitsCopy >>> 1);
+          ce.hits.reset();
+          ce.hits.add(ce.hitsCopy >>> 1);
         }
         if (tree.size() < wantToRemove) {
           tree.add(ce);
@@ -342,9 +345,9 @@ public class ConcurrentLFUCache<K, V> implements Cache<K,V>, Accountable {
 
   private void postRemoveEntry(CacheEntry<K, V> o) {
     if (o == null) return;
-    ramBytes.addAndGet(-(o.ramBytesUsed() + HASHTABLE_RAM_BYTES_PER_ENTRY));
-    stats.size.decrementAndGet();
-    stats.evictionCounter.incrementAndGet();
+    ramBytes.add(-(o.ramBytesUsed() + HASHTABLE_RAM_BYTES_PER_ENTRY));
+    stats.size.decrement();
+    stats.evictionCounter.increment();
     if (evictionListener != null) evictionListener.evictedEntry(o.key, o.value);
   }
 
@@ -367,7 +370,7 @@ public class ConcurrentLFUCache<K, V> implements Cache<K,V>, Accountable {
     try {
       for (Map.Entry<Object, CacheEntry<K, V>> entry : map.entrySet()) {
         CacheEntry<K, V> ce = entry.getValue();
-        ce.hitsCopy = ce.hits.get();
+        ce.hitsCopy = ce.hits.longValue();
         ce.lastAccessedCopy = ce.lastAccessed;
         if (tree.size() < n) {
           tree.add(ce);
@@ -411,7 +414,7 @@ public class ConcurrentLFUCache<K, V> implements Cache<K,V>, Accountable {
     try {
       for (Map.Entry<Object, CacheEntry<K, V>> entry : map.entrySet()) {
         CacheEntry<K, V> ce = entry.getValue();
-        ce.hitsCopy = ce.hits.get();
+        ce.hitsCopy = ce.hits.longValue();
         ce.lastAccessedCopy = ce.lastAccessed;
         if (tree.size() < n) {
           tree.add(ce);
@@ -437,13 +440,13 @@ public class ConcurrentLFUCache<K, V> implements Cache<K,V>, Accountable {
   }
 
   public int size() {
-    return stats.size.get();
+    return stats.size.intValue();
   }
 
   @Override
   public void clear() {
     map.clear();
-    ramBytes.set(0);
+    ramBytes.reset();
   }
 
   public Map<Object, CacheEntry<K, V>> getMap() {
@@ -452,7 +455,7 @@ public class ConcurrentLFUCache<K, V> implements Cache<K,V>, Accountable {
 
   @Override
   public long ramBytesUsed() {
-    return BASE_RAM_BYTES_USED + ramBytes.get();
+    return BASE_RAM_BYTES_USED + ramBytes.sum();
   }
 
   public static class CacheEntry<K, V> implements Comparable<CacheEntry<K, V>>, Accountable {
@@ -463,7 +466,7 @@ public class ConcurrentLFUCache<K, V> implements Cache<K,V>, Accountable {
     final K key;
     final V value;
     final long ramBytesUsed;
-    volatile AtomicLong hits = new AtomicLong(0);
+    final LongAdder hits = new LongAdder();
     long hitsCopy = 0;
     volatile long lastAccessed = 0;
     long lastAccessedCopy = 0;
@@ -500,7 +503,7 @@ public class ConcurrentLFUCache<K, V> implements Cache<K,V>, Accountable {
 
     @Override
     public String toString() {
-      return "key: " + key + " value: " + value + " hits:" + hits.get();
+      return "key: " + key + " value: " + value + " hits:" + hits.longValue();
     }
 
     @Override
@@ -529,57 +532,63 @@ public class ConcurrentLFUCache<K, V> implements Cache<K,V>, Accountable {
   public static class Stats implements Accountable {
     private static final long RAM_BYTES_USED =
         RamUsageEstimator.shallowSizeOfInstance(Stats.class) +
-            6 * RamUsageEstimator.primitiveSizes.get(long.class) +
-            RamUsageEstimator.primitiveSizes.get(int.class);
-
-    private final AtomicLong accessCounter = new AtomicLong(0),
-        putCounter = new AtomicLong(0),
-        nonLivePutCounter = new AtomicLong(0),
-        missCounter = new AtomicLong();
-    private final AtomicInteger size = new AtomicInteger();
-    private AtomicLong evictionCounter = new AtomicLong();
-    private AtomicLong evictionIdleCounter = new AtomicLong();
+            // LongAdder
+            7 * (
+                RamUsageEstimator.NUM_BYTES_ARRAY_HEADER +
+                    RamUsageEstimator.primitiveSizes.get(long.class) +
+                    2 * (RamUsageEstimator.NUM_BYTES_OBJECT_REF + RamUsageEstimator.primitiveSizes.get(long.class))
+            );
+
+    private final LongAdder accessCounter = new LongAdder();
+    private final LongAdder putCounter = new LongAdder();
+    private final LongAdder nonLivePutCounter = new LongAdder();
+    private final LongAdder missCounter = new LongAdder();
+    private final LongAdder size = new LongAdder();
+    private LongAdder evictionCounter = new LongAdder();
+    private LongAdder evictionIdleCounter = new LongAdder();
 
     public long getCumulativeLookups() {
-      return (accessCounter.get() - putCounter.get() - nonLivePutCounter.get()) + missCounter.get();
+      return (accessCounter.longValue() - putCounter.longValue() - nonLivePutCounter.longValue()) + missCounter.longValue();
     }
 
     public long getCumulativeHits() {
-      return accessCounter.get() - putCounter.get() - nonLivePutCounter.get();
+      return accessCounter.longValue() - putCounter.longValue() - nonLivePutCounter.longValue();
     }
 
     public long getCumulativePuts() {
-      return putCounter.get();
+      return putCounter.longValue();
     }
 
     public long getCumulativeEvictions() {
-      return evictionCounter.get();
+      return evictionCounter.longValue();
     }
 
     public long getCumulativeIdleEvictions() {
-      return evictionIdleCounter.get();
+      return evictionIdleCounter.longValue();
     }
 
     public int getCurrentSize() {
-      return size.get();
+      return size.intValue();
     }
 
     public long getCumulativeNonLivePuts() {
-      return nonLivePutCounter.get();
+      return nonLivePutCounter.longValue();
     }
 
     public long getCumulativeMisses() {
-      return missCounter.get();
+      return missCounter.longValue();
     }
 
     public void add(Stats other) {
-      accessCounter.addAndGet(other.accessCounter.get());
-      putCounter.addAndGet(other.putCounter.get());
-      nonLivePutCounter.addAndGet(other.nonLivePutCounter.get());
-      missCounter.addAndGet(other.missCounter.get());
-      evictionCounter.addAndGet(other.evictionCounter.get());
-      evictionIdleCounter.addAndGet(other.evictionIdleCounter.get());
-      size.set(Math.max(size.get(), other.size.get()));
+      accessCounter.add(other.accessCounter.longValue());
+      putCounter.add(other.putCounter.longValue());
+      nonLivePutCounter.add(other.nonLivePutCounter.longValue());
+      missCounter.add(other.missCounter.longValue());
+      evictionCounter.add(other.evictionCounter.longValue());
+      evictionIdleCounter.add(other.evictionIdleCounter.longValue());
+      long maxSize = Math.max(size.longValue(), other.size.longValue());
+      size.reset();
+      size.add(maxSize);
     }
 
     @Override
diff --git a/solr/core/src/java/org/apache/solr/util/ConcurrentLRUCache.java b/solr/core/src/java/org/apache/solr/util/ConcurrentLRUCache.java
index b6bf2a1..61793d8 100644
--- a/solr/core/src/java/org/apache/solr/util/ConcurrentLRUCache.java
+++ b/solr/core/src/java/org/apache/solr/util/ConcurrentLRUCache.java
@@ -32,7 +32,7 @@ import java.util.Map;
 import java.util.TreeSet;
 import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.TimeUnit;
-import java.util.concurrent.atomic.AtomicInteger;
+//import java.util.concurrent.atomic.AtomicInteger;
 import java.util.concurrent.atomic.AtomicLong;
 import java.util.concurrent.atomic.LongAdder;
 import java.util.concurrent.locks.ReentrantLock;
@@ -78,7 +78,7 @@ public class ConcurrentLRUCache<K,V> implements Cache<K,V>, Accountable {
   private boolean runCleanupThread;
 
   private long ramLowerWatermark, ramUpperWatermark;
-  private final AtomicLong ramBytes = new AtomicLong(0);
+  private final LongAdder ramBytes = new LongAdder();
 
   public ConcurrentLRUCache(long ramLowerWatermark, long ramUpperWatermark,
                             boolean runCleanupThread, EvictionListener<K, V> evictionListener) {
@@ -202,8 +202,8 @@ public class ConcurrentLRUCache<K,V> implements Cache<K,V>, Accountable {
   public V remove(K key) {
     CacheEntry<K,V> cacheEntry = map.remove(key);
     if (cacheEntry != null) {
-      stats.size.decrementAndGet();
-      ramBytes.addAndGet(-cacheEntry.ramBytesUsed() - HASHTABLE_RAM_BYTES_PER_ENTRY);
+      stats.size.decrement();
+      ramBytes.add(-cacheEntry.ramBytesUsed() - HASHTABLE_RAM_BYTES_PER_ENTRY);
       return cacheEntry.value;
     }
     return null;
@@ -226,12 +226,13 @@ public class ConcurrentLRUCache<K,V> implements Cache<K,V>, Accountable {
     CacheEntry<K,V> oldCacheEntry = map.put(e.key, e);
     int currentSize;
     if (oldCacheEntry == null) {
-      currentSize = stats.size.incrementAndGet();
-      ramBytes.addAndGet(e.ramBytesUsed() + HASHTABLE_RAM_BYTES_PER_ENTRY); // added key + value + entry
+      stats.size.increment();
+      currentSize = stats.size.intValue();
+      ramBytes.add(e.ramBytesUsed() + HASHTABLE_RAM_BYTES_PER_ENTRY); // added key + value + entry
     } else {
-      currentSize = stats.size.get();
-      ramBytes.addAndGet(-oldCacheEntry.ramBytesUsed());
-      ramBytes.addAndGet(e.ramBytesUsed());
+      currentSize = stats.size.intValue();
+      ramBytes.add(-oldCacheEntry.ramBytesUsed());
+      ramBytes.add(e.ramBytesUsed());
     }
     if (islive) {
       stats.putCounter.increment();
@@ -250,7 +251,7 @@ public class ConcurrentLRUCache<K,V> implements Cache<K,V>, Accountable {
     // Thread safety note: isCleaning read is piggybacked (comes after) other volatile reads
     // in this method.
     long idleCutoff = timeSource.getEpochTimeNs() - maxIdleTimeNs;
-    if ((currentSize > upperWaterMark || ramBytes.get() > ramUpperWatermark || oldestEntryNs.get() < idleCutoff) && !isCleaning) {
+    if ((currentSize > upperWaterMark || ramBytes.sum() > ramUpperWatermark || oldestEntryNs.get() < idleCutoff) && !isCleaning) {
       if (newThreadForCleanup) {
         new Thread(this::markAndSweep).start();
       } else if (cleanupThread != null){
@@ -311,7 +312,7 @@ public class ConcurrentLRUCache<K,V> implements Cache<K,V>, Accountable {
       Map.Entry<Object, CacheEntry<K, V>> entry = iterator.next();
       if (entry.getValue().createTime < idleCutoff) {
         iterator.remove();
-        stats.evictionIdleCounter.incrementAndGet();
+        stats.evictionIdleCounter.increment();
         postRemoveEntry(entry.getValue());
       } else {
         if (entry.getValue().createTime < currentOldestEntry) {
@@ -341,7 +342,7 @@ public class ConcurrentLRUCache<K,V> implements Cache<K,V>, Accountable {
     for (int i = entriesInAccessOrder.size() - 1; i >= 0; i--) {
       CacheEntry<K, V> kvCacheEntry = entriesInAccessOrder.get(i);
       evictEntry(kvCacheEntry.key);
-      if (ramBytes.get() <= ramLowerWatermark)  {
+      if (ramBytes.sum() <= ramLowerWatermark)  {
         break; // we are done!
       }
     }
@@ -366,7 +367,7 @@ public class ConcurrentLRUCache<K,V> implements Cache<K,V>, Accountable {
     this.oldestEntry = oldestEntry;     // volatile write to make isCleaning visible
 
     long timeCurrent = stats.accessCounter.longValue();
-    int sz = stats.size.get();
+    int sz = stats.size.intValue();
 
     int numRemoved = 0;
     int numKept = 0;
@@ -585,9 +586,9 @@ public class ConcurrentLRUCache<K,V> implements Cache<K,V>, Accountable {
 
   private void postRemoveEntry(CacheEntry<K, V> o) {
     if (o == null) return;
-    ramBytes.addAndGet(-(o.ramBytesUsed() + HASHTABLE_RAM_BYTES_PER_ENTRY));
-    stats.size.decrementAndGet();
-    stats.evictionCounter.incrementAndGet();
+    ramBytes.add(-(o.ramBytesUsed() + HASHTABLE_RAM_BYTES_PER_ENTRY));
+    stats.size.decrement();
+    stats.evictionCounter.increment();
     if(evictionListener != null) evictionListener.evictedEntry(o.key,o.value);
   }
 
@@ -657,13 +658,13 @@ public class ConcurrentLRUCache<K,V> implements Cache<K,V>, Accountable {
   }
 
   public int size() {
-    return stats.size.get();
+    return stats.size.intValue();
   }
 
   @Override
   public void clear() {
     map.clear();
-    ramBytes.set(0);
+    ramBytes.reset();
   }
 
   public Map<Object, CacheEntry<K,V>> getMap() {
@@ -749,23 +750,21 @@ public class ConcurrentLRUCache<K,V> implements Cache<K,V>, Accountable {
         // accounts for field refs
         RamUsageEstimator.shallowSizeOfInstance(Stats.class) +
             // LongAdder
-            3 * (
+            6 * (
                 RamUsageEstimator.NUM_BYTES_ARRAY_HEADER +
                 RamUsageEstimator.primitiveSizes.get(long.class) +
                 2 * (RamUsageEstimator.NUM_BYTES_OBJECT_REF + RamUsageEstimator.primitiveSizes.get(long.class))
             ) +
             // AtomicLong
-            3 * RamUsageEstimator.primitiveSizes.get(long.class) +
-            // AtomicInteger
-            RamUsageEstimator.primitiveSizes.get(int.class);
+            RamUsageEstimator.primitiveSizes.get(long.class);
 
     private final AtomicLong accessCounter = new AtomicLong(0);
     private final LongAdder putCounter = new LongAdder();
     private final LongAdder nonLivePutCounter = new LongAdder();
     private final LongAdder missCounter = new LongAdder();
-    private final AtomicInteger size = new AtomicInteger();
-    private AtomicLong evictionCounter = new AtomicLong();
-    private AtomicLong evictionIdleCounter = new AtomicLong();
+    private final LongAdder size = new LongAdder();
+    private LongAdder evictionCounter = new LongAdder();
+    private LongAdder evictionIdleCounter = new LongAdder();
 
     public long getCumulativeLookups() {
       return (accessCounter.longValue() - putCounter.longValue() - nonLivePutCounter.longValue()) + missCounter.longValue();
@@ -780,15 +779,15 @@ public class ConcurrentLRUCache<K,V> implements Cache<K,V>, Accountable {
     }
 
     public long getCumulativeEvictions() {
-      return evictionCounter.get();
+      return evictionCounter.longValue();
     }
 
     public long getCumulativeIdleEvictions() {
-      return evictionIdleCounter.get();
+      return evictionIdleCounter.longValue();
     }
 
     public int getCurrentSize() {
-      return size.get();
+      return size.intValue();
     }
 
     public long getCumulativeNonLivePuts() {
@@ -804,8 +803,10 @@ public class ConcurrentLRUCache<K,V> implements Cache<K,V>, Accountable {
       putCounter.add(other.putCounter.longValue());
       nonLivePutCounter.add(other.nonLivePutCounter.longValue());
       missCounter.add(other.missCounter.longValue());
-      evictionCounter.addAndGet(other.evictionCounter.get());
-      size.set(Math.max(size.get(), other.size.get()));
+      evictionCounter.add(other.evictionCounter.longValue());
+      long maxSize = Math.max(size.longValue(), other.size.longValue());
+      size.reset();
+      size.add(maxSize);
     }
 
     @Override
@@ -862,7 +863,7 @@ public class ConcurrentLRUCache<K,V> implements Cache<K,V>, Accountable {
 
   @Override
   public long ramBytesUsed() {
-    return BASE_RAM_BYTES_USED + ramBytes.get();
+    return BASE_RAM_BYTES_USED + ramBytes.sum();
   }
 
   @Override
diff --git a/solr/core/src/test/org/apache/solr/search/TestCaffeineCache.java b/solr/core/src/test/org/apache/solr/search/TestCaffeineCache.java
new file mode 100644
index 0000000..ae7a762
--- /dev/null
+++ b/solr/core/src/test/org/apache/solr/search/TestCaffeineCache.java
@@ -0,0 +1,285 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.solr.search;
+
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicReference;
+
+import com.github.benmanes.caffeine.cache.RemovalCause;
+import org.apache.lucene.util.Accountable;
+import org.apache.lucene.util.TestUtil;
+import org.apache.solr.SolrTestCase;
+import org.apache.solr.metrics.SolrMetricManager;
+import org.junit.Test;
+
+import com.github.benmanes.caffeine.cache.Cache;
+import com.github.benmanes.caffeine.cache.Caffeine;
+
+/**
+ * Test for {@link CaffeineCache}.
+ */
+public class TestCaffeineCache extends SolrTestCase {
+
+  SolrMetricManager metricManager = new SolrMetricManager();
+  String registry = TestUtil.randomSimpleString(random(), 2, 10);
+  String scope = TestUtil.randomSimpleString(random(), 2, 10);
+
+  @Test
+  public void testSimple() throws IOException {
+    CaffeineCache<Integer, String> lfuCache = new CaffeineCache<>();
+    lfuCache.initializeMetrics(metricManager, registry, "foo", scope + "-1");
+
+    CaffeineCache<Integer, String> newLFUCache = new CaffeineCache<>();
+    newLFUCache.initializeMetrics(metricManager, registry, "foo2", scope + "-2");
+
+    Map<String, String> params = new HashMap<>();
+    params.put("size", "100");
+    params.put("initialSize", "10");
+    params.put("autowarmCount", "25");
+
+    NoOpRegenerator regenerator = new NoOpRegenerator();
+    Object initObj = lfuCache.init(params, null, regenerator);
+    lfuCache.setState(SolrCache.State.LIVE);
+    for (int i = 0; i < 101; i++) {
+      lfuCache.put(i + 1, Integer.toString(i + 1));
+    }
+    assertEquals("15", lfuCache.get(15));
+    assertEquals("75", lfuCache.get(75));
+    assertEquals(null, lfuCache.get(110));
+    Map<String, Object> nl = lfuCache.getMetricsMap().getValue();
+    assertEquals(3L, nl.get("lookups"));
+    assertEquals(2L, nl.get("hits"));
+    assertEquals(101L, nl.get("inserts"));
+
+    assertEquals(null, lfuCache.get(1));  // first item put in should be the first out
+
+    // Test autowarming
+    newLFUCache.init(params, initObj, regenerator);
+    newLFUCache.warm(null, lfuCache);
+    newLFUCache.setState(SolrCache.State.LIVE);
+
+    newLFUCache.put(103, "103");
+    assertEquals("15", newLFUCache.get(15));
+    assertEquals("75", newLFUCache.get(75));
+    assertEquals(null, newLFUCache.get(50));
+    nl = newLFUCache.getMetricsMap().getValue();
+    assertEquals(3L, nl.get("lookups"));
+    assertEquals(2L, nl.get("hits"));
+    assertEquals(1L, nl.get("inserts"));
+    assertEquals(0L, nl.get("evictions"));
+
+    assertEquals(7L, nl.get("cumulative_lookups"));
+    assertEquals(4L, nl.get("cumulative_hits"));
+    assertEquals(102L, nl.get("cumulative_inserts"));
+  }
+
+  @Test
+  public void testTimeDecay() {
+    Cache<Integer, String> cacheDecay = Caffeine.newBuilder()
+        .executor(Runnable::run)
+        .maximumSize(20)
+        .build();
+    for (int i = 1; i < 21; i++) {
+      cacheDecay.put(i, Integer.toString(i));
+    }
+    Map<Integer, String> itemsDecay;
+
+    // Now increase the freq count for 5 items
+    for (int i = 0; i < 5; ++i) {
+      for (int j = 0; j < 10; ++j) {
+        cacheDecay.getIfPresent(i + 13);
+      }
+    }
+    // OK, 13 - 17 should have larger counts and should stick past next few collections
+    cacheDecay.put(22, "22");
+    cacheDecay.put(23, "23");
+    cacheDecay.put(24, "24");
+    cacheDecay.put(25, "25");
+    itemsDecay = cacheDecay.policy().eviction().get().hottest(10);
+    // 13 - 17 should be in cache, but 11 and 18 (among others) should not. Testing that elements before and
+    // after the ones with increased counts are removed, and all the increased count ones are still in the cache
+    assertNull(itemsDecay.get(11));
+    assertNull(itemsDecay.get(18));
+    assertNotNull(itemsDecay.get(13));
+    assertNotNull(itemsDecay.get(14));
+    assertNotNull(itemsDecay.get(15));
+    assertNotNull(itemsDecay.get(16));
+    assertNotNull(itemsDecay.get(17));
+
+
+    // Testing that all the elements in front of the ones with increased counts are gone
+    for (int idx = 26; idx < 32; ++idx) {
+      cacheDecay.put(idx, Integer.toString(idx));
+    }
+    //Surplus count should be at 0
+    itemsDecay = cacheDecay.policy().eviction().get().hottest(10);
+    assertNull(itemsDecay.get(20));
+    assertNull(itemsDecay.get(24));
+    assertNotNull(itemsDecay.get(13));
+    assertNotNull(itemsDecay.get(14));
+    assertNotNull(itemsDecay.get(15));
+    assertNotNull(itemsDecay.get(16));
+    assertNotNull(itemsDecay.get(17));
+  }
+
+  @Test
+  public void testMaxIdleTime() throws Exception {
+    int IDLE_TIME_SEC = 5;
+    CountDownLatch removed = new CountDownLatch(1);
+    AtomicReference<RemovalCause> removalCause = new AtomicReference<>();
+    CaffeineCache<String, String> cache = new CaffeineCache<>() {
+      @Override
+      public void onRemoval(String key, String value, RemovalCause cause) {
+        super.onRemoval(key, value, cause);
+        removalCause.set(cause);
+        removed.countDown();
+      }
+    };
+    Map<String, String> params = new HashMap<>();
+    params.put("size", "6");
+    params.put("maxIdleTime", "" + IDLE_TIME_SEC);
+    cache.init(params, null, new NoOpRegenerator());
+
+    cache.put("foo", "bar");
+    assertEquals("bar", cache.get("foo"));
+    // sleep for at least the idle time before inserting other entries
+    // the eviction is piggy-backed on put()
+    Thread.sleep(TimeUnit.SECONDS.toMillis(IDLE_TIME_SEC * 2));
+    cache.put("abc", "xyz");
+    boolean await = removed.await(30, TimeUnit.SECONDS);
+    assertTrue("did not expire entry in in time", await);
+    assertEquals(RemovalCause.EXPIRED, removalCause.get());
+    assertNull(cache.get("foo"));
+  }
+
+  @Test
+  public void testSetLimits() throws Exception {
+    AtomicReference<CountDownLatch> removed = new AtomicReference<>(new CountDownLatch(2));
+    List<RemovalCause> removalCauses = new ArrayList<>();
+    List<String> removedKeys = new ArrayList<>();
+    Set<String> allKeys = new HashSet<>();
+    CaffeineCache<String, Accountable> cache = new CaffeineCache<>() {
+      @Override
+      public Accountable put(String key, Accountable val) {
+        allKeys.add(key);
+        return super.put(key, val);
+      }
+
+      @Override
+      public void onRemoval(String key, Accountable value, RemovalCause cause) {
+        super.onRemoval(key, value, cause);
+        removalCauses.add(cause);
+        removedKeys.add(key);
+        removed.get().countDown();
+      }
+    };
+    Map<String, String> params = new HashMap<>();
+    params.put("size", "5");
+    cache.init(params, null, new NoOpRegenerator());
+
+    for (int i = 0; i < 5; i++) {
+      cache.put("foo-" + i, new Accountable() {
+        @Override
+        public long ramBytesUsed() {
+          return 1024 * 1024;
+        }
+      });
+    }
+    assertEquals(5, cache.size());
+    // no evictions yet
+    assertEquals(2, removed.get().getCount());
+
+    cache.put("abc1", new Accountable() {
+      @Override
+      public long ramBytesUsed() {
+        return 1;
+      }
+    });
+    cache.put("abc2", new Accountable() {
+      @Override
+      public long ramBytesUsed() {
+        return 2;
+      }
+    });
+    boolean await = removed.get().await(30, TimeUnit.SECONDS);
+    assertTrue("did not evict entries in in time", await);
+    assertEquals(5, cache.size());
+    assertEquals(2, cache.get("abc2").ramBytesUsed());
+    for (String key : removedKeys) {
+      assertNull("key " + key + " still present!", cache.get(key));
+      allKeys.remove(key);
+    }
+    for (RemovalCause cause : removalCauses) {
+      assertEquals(RemovalCause.SIZE, cause);
+    }
+
+    removed.set(new CountDownLatch(2));
+    removalCauses.clear();
+    removedKeys.clear();
+    // trim down by item count
+    cache.setMaxSize(3);
+    cache.put("abc3",  new Accountable() {
+      @Override
+      public long ramBytesUsed() {
+        return 3;
+      }
+    });
+    await = removed.get().await(30, TimeUnit.SECONDS);
+    assertTrue("did not evict entries in in time", await);
+    assertEquals(3, cache.size());
+    for (String key : removedKeys) {
+      assertNull("key " + key + " still present!", cache.get(key));
+      allKeys.remove(key);
+    }
+    for (RemovalCause cause : removalCauses) {
+      assertEquals(RemovalCause.SIZE, cause);
+    }
+
+    // at least one item has to go
+    removed.set(new CountDownLatch(1));
+    removalCauses.clear();
+    removedKeys.clear();
+    // trim down by ram size
+    cache.setMaxRamMB(1);
+    await = removed.get().await(30, TimeUnit.SECONDS);
+    assertTrue("did not evict entries in in time", await);
+    for (String key : removedKeys) {
+      assertNull("key " + key + " still present!", cache.get(key));
+      allKeys.remove(key);
+    }
+    for (RemovalCause cause : removalCauses) {
+      assertEquals(RemovalCause.SIZE, cause);
+    }
+    // check total size of remaining items
+    long total = 0;
+    for (String key : allKeys) {
+      Accountable a = cache.get(key);
+      assertNotNull("missing value for key " + key, a);
+      total += a.ramBytesUsed();
+    }
+    assertTrue("total ram bytes should be greater than 0", total > 0);
+    assertTrue("total ram bytes exceeded limit", total < 1024 * 1024);
+  }
+}
diff --git a/solr/core/src/test/org/apache/solr/search/TestFastLRUCache.java b/solr/core/src/test/org/apache/solr/search/TestFastLRUCache.java
index 5844dac..f490e20 100644
--- a/solr/core/src/test/org/apache/solr/search/TestFastLRUCache.java
+++ b/solr/core/src/test/org/apache/solr/search/TestFastLRUCache.java
@@ -16,6 +16,7 @@
  */
 package org.apache.solr.search;
 
+import org.apache.commons.math3.stat.descriptive.SummaryStatistics;
 import org.apache.lucene.index.Term;
 import org.apache.lucene.search.Query;
 import org.apache.lucene.search.WildcardQuery;
@@ -33,6 +34,7 @@ import java.io.IOException;
 import java.util.HashMap;
 import java.util.Map;
 import java.util.Random;
+import java.util.TreeMap;
 import java.util.concurrent.CountDownLatch;
 import java.util.concurrent.TimeUnit;
 import java.util.concurrent.atomic.AtomicInteger;
@@ -471,7 +473,7 @@ public class TestFastLRUCache extends SolrTestCase {
   }
 
 
-  void cachePerfTest(final SolrCache sc, final int nThreads, final int numGets, int cacheSize, final int maxKey) {
+  double[] cachePerfTest(final SolrCache sc, final int nThreads, final int numGets, int cacheSize, final int maxKey) {
     Map l = new HashMap();
     l.put("size", ""+cacheSize);
     l.put("initialSize", ""+cacheSize);
@@ -512,37 +514,73 @@ public class TestFastLRUCache extends SolrTestCase {
       }
     }
 
-    System.out.println("time=" + timer.getTime() + " impl=" +sc.getClass().getSimpleName()
-                       +" nThreads= " + nThreads + " size="+cacheSize+" maxKey="+maxKey+" gets="+numGets
-                       +" hitRatio="+(1-(((double)puts.get())/numGets)));
+    double time = timer.getTime();
+    double hitRatio = (1-(((double)puts.get())/numGets));
+//    System.out.println("time=" + time + " impl=" +sc.getClass().getSimpleName()
+//                       +" nThreads= " + nThreads + " size="+cacheSize+" maxKey="+maxKey+" gets="+numGets
+//                       +" hitRatio="+(1-(((double)puts.get())/numGets)));
+    return new double[]{time, hitRatio};
   }
 
-  void perfTestBoth(int nThreads, int numGets, int cacheSize, int maxKey) {
-    cachePerfTest(new LRUCache(), nThreads, numGets, cacheSize, maxKey);
-    cachePerfTest(new FastLRUCache(), nThreads, numGets, cacheSize, maxKey);
+  private int NUM_RUNS = 5;
+  void perfTestBoth(int maxThreads, int numGets, int cacheSize, int maxKey,
+                    Map<String, Map<String, SummaryStatistics>> timeStats,
+                    Map<String, Map<String, SummaryStatistics>> hitStats) {
+    for (int nThreads = 1 ; nThreads <= maxThreads; nThreads++) {
+      String testKey = "threads=" + nThreads + ",gets=" + numGets + ",size=" + cacheSize + ",maxKey=" + maxKey;
+      System.err.println(testKey);
+      for (int i = 0; i < NUM_RUNS; i++) {
+        double[] data = cachePerfTest(new LRUCache(), nThreads, numGets, cacheSize, maxKey);
+        timeStats.computeIfAbsent(testKey, k -> new TreeMap<>())
+            .computeIfAbsent("LRUCache", k -> new SummaryStatistics())
+            .addValue(data[0]);
+        hitStats.computeIfAbsent(testKey, k -> new TreeMap<>())
+            .computeIfAbsent("LRUCache", k -> new SummaryStatistics())
+            .addValue(data[1]);
+        data = cachePerfTest(new CaffeineCache(), nThreads, numGets, cacheSize, maxKey);
+        timeStats.computeIfAbsent(testKey, k -> new TreeMap<>())
+            .computeIfAbsent("CaffeineCache", k -> new SummaryStatistics())
+            .addValue(data[0]);
+        hitStats.computeIfAbsent(testKey, k -> new TreeMap<>())
+            .computeIfAbsent("CaffeineCache", k -> new SummaryStatistics())
+            .addValue(data[1]);
+        data = cachePerfTest(new FastLRUCache(), nThreads, numGets, cacheSize, maxKey);
+        timeStats.computeIfAbsent(testKey, k -> new TreeMap<>())
+            .computeIfAbsent("FastLRUCache", k -> new SummaryStatistics())
+            .addValue(data[0]);
+        hitStats.computeIfAbsent(testKey, k -> new TreeMap<>())
+            .computeIfAbsent("FastLRUCache", k -> new SummaryStatistics())
+            .addValue(data[1]);
+      }
+    }
   }
 
+  int NUM_THREADS = 4;
   /***
       public void testCachePerf() {
+        Map<String, Map<String, SummaryStatistics>> timeStats = new TreeMap<>();
+        Map<String, Map<String, SummaryStatistics>> hitStats = new TreeMap<>();
       // warmup
-      perfTestBoth(2, 100000, 100000, 120000);
-      perfTestBoth(1, 2000000, 100000, 100000); // big cache, 100% hit ratio
-      perfTestBoth(2, 2000000, 100000, 100000); // big cache, 100% hit ratio
-      perfTestBoth(1, 2000000, 100000, 120000); // big cache, bigger hit ratio
-      perfTestBoth(2, 2000000, 100000, 120000); // big cache, bigger hit ratio
-      perfTestBoth(1, 2000000, 100000, 200000); // big cache, ~50% hit ratio
-      perfTestBoth(2, 2000000, 100000, 200000); // big cache, ~50% hit ratio
-      perfTestBoth(1, 2000000, 100000, 1000000); // big cache, ~10% hit ratio
-      perfTestBoth(2, 2000000, 100000, 1000000); // big cache, ~10% hit ratio
-
-      perfTestBoth(1, 2000000, 1000, 1000); // small cache, ~100% hit ratio
-      perfTestBoth(2, 2000000, 1000, 1000); // small cache, ~100% hit ratio
-      perfTestBoth(1, 2000000, 1000, 1200); // small cache, bigger hit ratio
-      perfTestBoth(2, 2000000, 1000, 1200); // small cache, bigger hit ratio
-      perfTestBoth(1, 2000000, 1000, 2000); // small cache, ~50% hit ratio
-      perfTestBoth(2, 2000000, 1000, 2000); // small cache, ~50% hit ratio
-      perfTestBoth(1, 2000000, 1000, 10000); // small cache, ~10% hit ratio
-      perfTestBoth(2, 2000000, 1000, 10000); // small cache, ~10% hit ratio
+      perfTestBoth(NUM_THREADS, 100000, 100000, 120000, new HashMap<>(), new HashMap());
+
+      perfTestBoth(NUM_THREADS, 2000000, 100000, 100000, timeStats, hitStats); // big cache, 100% hit ratio
+      perfTestBoth(NUM_THREADS, 2000000, 100000, 120000, timeStats, hitStats); // big cache, bigger hit ratio
+      perfTestBoth(NUM_THREADS, 2000000, 100000, 200000, timeStats, hitStats); // big cache, ~50% hit ratio
+      perfTestBoth(NUM_THREADS, 2000000, 100000, 1000000, timeStats, hitStats); // big cache, ~10% hit ratio
+
+      perfTestBoth(NUM_THREADS, 2000000, 1000, 1000, timeStats, hitStats); // small cache, ~100% hit ratio
+      perfTestBoth(NUM_THREADS, 2000000, 1000, 1200, timeStats, hitStats); // small cache, bigger hit ratio
+      perfTestBoth(NUM_THREADS, 2000000, 1000, 2000, timeStats, hitStats); // small cache, ~50% hit ratio
+      perfTestBoth(NUM_THREADS, 2000000, 1000, 10000, timeStats, hitStats); // small cache, ~10% hit ratio
+
+        System.out.println("\n=====================\n");
+        timeStats.forEach((testKey, map) -> {
+          Map<String, SummaryStatistics> hits = hitStats.get(testKey);
+          System.out.println("* " + testKey);
+          map.forEach((type, summary) -> {
+            System.out.println("\t" + String.format("%14s", type) + "\ttime " + summary.getMean() + "\thitRatio " + hits.get(type).getMean());
+          });
+        });
       }
   ***/
 
diff --git a/solr/core/src/test/org/apache/solr/store/blockcache/BlockCacheTest.java b/solr/core/src/test/org/apache/solr/store/blockcache/BlockCacheTest.java
index 3a44673..2ea3bf0 100644
--- a/solr/core/src/test/org/apache/solr/store/blockcache/BlockCacheTest.java
+++ b/solr/core/src/test/org/apache/solr/store/blockcache/BlockCacheTest.java
@@ -44,10 +44,10 @@ public class BlockCacheTest extends SolrTestCase {
   public void testBlockCache() {
     int blocksInTest = 2000000;
     int blockSize = 1024;
-    
+
     int slabSize = blockSize * 4096;
     long totalMemory = 2 * slabSize;
-    
+
     BlockCache blockCache = new BlockCache(new Metrics(), true, totalMemory, slabSize, blockSize);
     byte[] buffer = new byte[1024];
     Random random = random();
@@ -82,7 +82,7 @@ public class BlockCacheTest extends SolrTestCase {
       long t3 = System.nanoTime();
       if (blockCache.fetch(blockCacheKey, buffer)) {
         fetchTime += (System.nanoTime() - t3);
-        assertTrue(Arrays.equals(testData, buffer));
+        assertTrue("buffer content differs", Arrays.equals(testData, buffer));
       }
     }
     System.out.println("Cache Hits    = " + hitsInCache.get());
@@ -101,7 +101,7 @@ public class BlockCacheTest extends SolrTestCase {
   // always returns the same thing so we don't actually have to store the bytes redundantly to check them.
   private static byte getByte(long pos) {
     // knuth multiplicative hash method, then take top 8 bits
-    return (byte) ((((int)pos) * (int)(2654435761L)) >> 24);
+    return (byte) ((((int) pos) * (int) (2654435761L)) >> 24);
 
     // just the lower bits of the block number, to aid in debugging...
     // return (byte)(pos>>10);
@@ -117,17 +117,17 @@ public class BlockCacheTest extends SolrTestCase {
     final long totalMemory = 2 * slabSize;  // 2 slabs of memory, so only half of what is needed for all blocks
 
     /***
-    final int blocksInTest = 16384;  // pick something bigger than 256, since that would lead to a slab size of 64 blocks and the bitset locks would consist of a single word.
-    final int blockSize = 1024;
-    final int slabSize = blocksInTest * blockSize / 4;
-    final long totalMemory = 2 * slabSize;  // 2 slabs of memory, so only half of what is needed for all blocks
-    ***/
-
-    final int nThreads=64;
-    final int nReads=1000000;
-    final int readsPerThread=nReads/nThreads;
-    final int readLastBlockOdds=10; // odds (1 in N) of the next block operation being on the same block as the previous operation... helps flush concurrency issues
-    final int showErrors=50; // show first 50 validation failures
+     final int blocksInTest = 16384;  // pick something bigger than 256, since that would lead to a slab size of 64 blocks and the bitset locks would consist of a single word.
+     final int blockSize = 1024;
+     final int slabSize = blocksInTest * blockSize / 4;
+     final long totalMemory = 2 * slabSize;  // 2 slabs of memory, so only half of what is needed for all blocks
+     ***/
+
+    final int nThreads = 64;
+    final int nReads = 1000000;
+    final int readsPerThread = nReads / nThreads;
+    final int readLastBlockOdds = 10; // odds (1 in N) of the next block operation being on the same block as the previous operation... helps flush concurrency issues
+    final int showErrors = 50; // show first 50 validation failures
 
     final BlockCache blockCache = new BlockCache(new Metrics(), true, totalMemory, slabSize, blockSize);
 
@@ -142,7 +142,7 @@ public class BlockCacheTest extends SolrTestCase {
 
 
     Thread[] threads = new Thread[nThreads];
-    for (int i=0; i<threads.length; i++) {
+    for (int i = 0; i < threads.length; i++) {
       final int threadnum = i;
       final long seed = rnd.nextLong();
 
@@ -168,14 +168,15 @@ public class BlockCacheTest extends SolrTestCase {
         }
 
         public void test(int iter) {
-          for (int i=0; i<iter; i++) {
+          for (int i = 0; i < iter; i++) {
             test();
           }
         }
 
         public void test() {
           long block = r.nextInt(blocksInTest);
-          if (r.nextInt(readLastBlockOdds) == 0) block = lastBlock.get();  // some percent of the time, try to read the last block another thread was just reading/writing
+          if (r.nextInt(readLastBlockOdds) == 0)
+            block = lastBlock.get();  // some percent of the time, try to read the last block another thread was just reading/writing
           lastBlock.set(block);
 
 
@@ -192,7 +193,8 @@ public class BlockCacheTest extends SolrTestCase {
               long globalPos = globalOffset + i;
               if (buffer[i] != getByte(globalPos)) {
                 failed.set(true);
-                if (validateFails.incrementAndGet() <= showErrors) System.out.println("ERROR: read was " + "block=" + block + " blockOffset=" + blockOffset + " len=" + len + " globalPos=" + globalPos + " localReadOffset=" + i + " got=" + buffer[i] + " expected=" + getByte(globalPos));
+                if (validateFails.incrementAndGet() <= showErrors)
+                  System.out.println("ERROR: read was " + "block=" + block + " blockOffset=" + blockOffset + " len=" + len + " globalPos=" + globalPos + " localReadOffset=" + i + " got=" + buffer[i] + " expected=" + getByte(globalPos));
                 break;
               }
             }
@@ -229,7 +231,7 @@ public class BlockCacheTest extends SolrTestCase {
     System.out.println("Cache Store Fails = " + storeFails.get());
     System.out.println("Blocks with Errors = " + validateFails.get());
 
-    assertFalse( failed.get() );
+    assertFalse("cached bytes differ from expected", failed.get());
   }
 
 
@@ -245,12 +247,12 @@ public class BlockCacheTest extends SolrTestCase {
 
     // TODO: introduce more randomness in cache size, hit rate, etc
     final int blocksInTest = 400;
-    final int maxEntries = blocksInTest/2;
+    final int maxEntries = blocksInTest / 2;
 
-    final int nThreads=64;
-    final int nReads=1000000;
-    final int readsPerThread=nReads/nThreads;
-    final int readLastBlockOdds=10; // odds (1 in N) of the next block operation being on the same block as the previous operation... helps flush concurrency issues
+    final int nThreads = 64;
+    final int nReads = 1000000;
+    final int readsPerThread = nReads / nThreads;
+    final int readLastBlockOdds = 10; // odds (1 in N) of the next block operation being on the same block as the previous operation... helps flush concurrency issues
     final int updateAnywayOdds = 3; // sometimes insert a new entry for the key even if one was found
     final int invalidateOdds = 20; // sometimes invalidate an entry
 
@@ -258,17 +260,24 @@ public class BlockCacheTest extends SolrTestCase {
     final AtomicLong removals = new AtomicLong();
     final AtomicLong inserts = new AtomicLong();
 
-    RemovalListener<Long,Val> listener = (k, v, removalCause) -> {
-      assert v.key == k;
+    RemovalListener<Long, Val> listener = (k, v, removalCause) -> {
+      removals.incrementAndGet();
+      if (v == null) {
+        if (removalCause != RemovalCause.COLLECTED) {
+          throw new RuntimeException("Null value for key " + k + ", removalCause=" + removalCause);
+        } else {
+          return;
+        }
+      }
+      assertEquals("cache key differs from value's key", (Long) k, (Long) v.key);
       if (!v.live.compareAndSet(true, false)) {
         throw new RuntimeException("listener called more than once! k=" + k + " v=" + v + " removalCause=" + removalCause);
         // return;  // use this variant if listeners may be called more than once
       }
-      removals.incrementAndGet();
     };
 
 
-    com.github.benmanes.caffeine.cache.Cache<Long,Val> cache = Caffeine.newBuilder()
+    com.github.benmanes.caffeine.cache.Cache<Long, Val> cache = Caffeine.newBuilder()
         .removalListener(listener)
         .maximumSize(maxEntries)
         .executor(Runnable::run)
@@ -279,11 +288,12 @@ public class BlockCacheTest extends SolrTestCase {
     final AtomicLong maxObservedSize = new AtomicLong();
 
     Thread[] threads = new Thread[nThreads];
-    for (int i=0; i<threads.length; i++) {
+    for (int i = 0; i < threads.length; i++) {
       final long seed = rnd.nextLong();
 
       threads[i] = new Thread() {
         Random r;
+
         @Override
         public void run() {
           try {
@@ -296,13 +306,13 @@ public class BlockCacheTest extends SolrTestCase {
         }
 
         public void test(int iter) {
-          for (int i=0; i<iter; i++) {
+          for (int i = 0; i < iter; i++) {
             test();
           }
         }
 
         boolean odds(int odds) {
-          return odds > 0 && r.nextInt(odds)==0;
+          return odds > 0 && r.nextInt(odds) == 0;
         }
 
         long getBlock() {
@@ -329,7 +339,7 @@ public class BlockCacheTest extends SolrTestCase {
           Val v = cache.getIfPresent(k);
           if (v != null) {
             hits.incrementAndGet();
-            assert k.equals(v.key);
+            assertEquals("cache key differs from value's key", (Long) k, (Long) v.key);
           }
 
           if (v == null || odds(updateAnywayOdds)) {
@@ -358,13 +368,10 @@ public class BlockCacheTest extends SolrTestCase {
 
     // Thread.sleep(1000); // need to wait if executor is used for listener?
     long cacheSize = cache.estimatedSize();
-    System.out.println("Done! # of Elements = " + cacheSize + " inserts=" + inserts.get() + " removals=" + removals.get() + " hits=" + hits.get() +  " maxObservedSize=" + maxObservedSize);
-    assert inserts.get() - removals.get() == cacheSize;
-    assertFalse( failed.get() );
+    System.out.println("Done! # of Elements = " + cacheSize + " inserts=" + inserts.get() + " removals=" + removals.get() + " hits=" + hits.get() + " maxObservedSize=" + maxObservedSize);
+    assertEquals("cache size different from (inserts - removal)", cacheSize,  inserts.get() - removals.get());
+    assertFalse(failed.get());
   }
 
 
-
-
-
 }
diff --git a/solr/licenses/caffeine-2.4.0.jar.sha1 b/solr/licenses/caffeine-2.4.0.jar.sha1
deleted file mode 100644
index 9c317d9..0000000
--- a/solr/licenses/caffeine-2.4.0.jar.sha1
+++ /dev/null
@@ -1 +0,0 @@
-5aa8bbb851b1ad403cc140094ba4a25998369efe
diff --git a/solr/licenses/caffeine-2.8.0.jar.sha1 b/solr/licenses/caffeine-2.8.0.jar.sha1
new file mode 100644
index 0000000..ce291c4
--- /dev/null
+++ b/solr/licenses/caffeine-2.8.0.jar.sha1
@@ -0,0 +1 @@
+6000774d7f8412ced005a704188ced78beeed2bb
diff --git a/solr/solr-ref-guide/src/query-settings-in-solrconfig.adoc b/solr/solr-ref-guide/src/query-settings-in-solrconfig.adoc
index 3729e53..4b44cd8 100644
--- a/solr/solr-ref-guide/src/query-settings-in-solrconfig.adoc
+++ b/solr/solr-ref-guide/src/query-settings-in-solrconfig.adoc
@@ -33,22 +33,27 @@ Solr caches are associated with a specific instance of an Index Searcher, a spec
 
 When a new searcher is opened, the current searcher continues servicing requests while the new one auto-warms its cache. The new searcher uses the current searcher's cache to pre-populate its own. When the new searcher is ready, it is registered as the current searcher and begins handling all new search requests. The old searcher will be closed once it has finished servicing all its requests.
 
-In Solr, there are three cache implementations: `solr.search.LRUCache`, `solr.search.FastLRUCache,` and `solr.search.LFUCache`.
+=== Cache implementations
+In Solr, the following cache implementations are available: recommended `solr.search.CaffeineCache`, and legacy implementations: `solr.search.LRUCache`, `solr.search.FastLRUCache,` and `solr.search.LFUCache`.
+
+The `CaffeineCache` is an implementation backed by the https://github.com/ben-manes/caffeine[Caffeine caching library]. By default it uses a Window TinyLFU (W-TinyLFU) eviction policy, which allows the eviction based on both frequency and recency of use in O(1) time with a small footprint. Generally this cache implementation is recommended over other legacy caches as it usually offers lower memory footprint, higher hit ratio and better multi-threaded performance over legacy caches.
 
 The acronym LRU stands for Least Recently Used. When an LRU cache fills up, the entry with the oldest last-accessed timestamp is evicted to make room for the new entry. The net effect is that entries that are accessed frequently tend to stay in the cache, while those that are not accessed frequently tend to drop out and will be re-fetched from the index if needed again.
 
 The `FastLRUCache`, which was introduced in Solr 1.4, is designed to be lock-free, so it is well suited for caches which are hit several times in a request.
 
-Both `LRUCache` and `FastLRUCache` use an auto-warm count that supports both integers and percentages which get evaluated relative to the current size of the cache when warming happens.
+`CaffeineCache`, `LRUCache` and `FastLRUCache` use an auto-warm count that supports both integers and percentages which get evaluated relative to the current size of the cache when warming happens.
 
 The `LFUCache` refers to the Least Frequently Used cache. This works in a way similar to the LRU cache, except that when the cache fills up, the entry that has been used the least is evicted.
 
 The Statistics page in the Solr Admin UI will display information about the performance of all the active caches. This information can help you fine-tune the sizes of the various caches appropriately for your particular application. When a Searcher terminates, a summary of its cache usage is also written to the log.
 
-Each cache has settings to define its initial size (`initialSize`), maximum size (`size`) and number of items to use for during warming (`autowarmCount`). The LRU and FastLRU cache implementations can take a percentage instead of an absolute value for `autowarmCount`.
+Each cache has settings to define its initial size (`initialSize`), maximum size (`size`) and number of items to use for during warming (`autowarmCount`). The Caffeine, LRU and FastLRU cache implementations can take a percentage instead of an absolute value for `autowarmCount`.
 
 Each cache implementation also supports a `maxIdleTime` attribute that controls the automatic eviction of entries that haven't been used for a while. This attribute is expressed in seconds, with the default value of `0` meaning no entries are automatically evicted due to exceeded idle time. Smaller values of this attribute will cause older entries to be evicted quickly, which will reduce cache memory usage but may instead cause thrashing due to a repeating eviction-lookup-miss-insertion  [...]
 
+`CaffeineCache`, `LRUCache` and `FastLRUCache` support a `maxRamMB` attribute that limits the maximum amount of memory a cache may consume. When both `size` and `maxRamMB` limits are specified the behavior will differ among implementations: in `CaffeineCache` the `maxRamMB` limit will take precedence and the `size` limit will be ignored, while in `LRUCache` and `FastLRUCache` both limits will be observed, with entries being evicted whenever any of the limits is reached.
+
 `FastLRUCache` and `LFUCache` support `showItems` attribute. This is the number of cache items to display in the stats page for the cache. It is for debugging.
 
 Details of each cache are described below.


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