/*
* Copyright (C) 2011 The Guava Authors
*
* Licensed 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 com.google.common.cache;
import static com.google.common.base.Preconditions.checkArgument;
import com.google.common.annotations.Beta;
import com.google.common.annotations.GwtCompatible;
import com.google.common.base.MoreObjects;
import com.google.common.base.Objects;
import java.util.concurrent.Callable;
import javax.annotation.Nullable;
/**
* Statistics about the performance of a {@link Cache}. Instances of this class are immutable.
*
* <p>Cache statistics are incremented according to the following rules:
*
* <ul>
* <li>When a cache lookup encounters an existing cache entry {@code hitCount} is incremented.
* <li>When a cache lookup first encounters a missing cache entry, a new entry is loaded.
* <ul>
* <li>After successfully loading an entry {@code missCount} and {@code loadSuccessCount} are
* incremented, and the total loading time, in nanoseconds, is added to
* {@code totalLoadTime}.
* <li>When an exception is thrown while loading an entry, {@code missCount} and {@code
* loadExceptionCount} are incremented, and the total loading time, in nanoseconds, is
* added to {@code totalLoadTime}.
* <li>Cache lookups that encounter a missing cache entry that is still loading will wait
* for loading to complete (whether successful or not) and then increment {@code missCount}.
* </ul>
* <li>When an entry is evicted from the cache, {@code evictionCount} is incremented.
* <li>No stats are modified when a cache entry is invalidated or manually removed.
* <li>No stats are modified on a query to {@link Cache#getIfPresent}.
* <li>No stats are modified by operations invoked on the {@linkplain Cache#asMap asMap} view of
* the cache.
* </ul>
*
* <p>A lookup is specifically defined as an invocation of one of the methods
* {@link LoadingCache#get(Object)}, {@link LoadingCache#getUnchecked(Object)},
* {@link Cache#get(Object, Callable)}, or {@link LoadingCache#getAll(Iterable)}.
*
* @author Charles Fry
* @since 10.0
*/
@Beta
@GwtCompatible
public final class CacheStats {
private final long hitCount;
private final long missCount;
private final long loadSuccessCount;
private final long loadExceptionCount;
private final long totalLoadTime;
private final long evictionCount;
/**
* Constructs a new {@code CacheStats} instance.
*
* <p>Five parameters of the same type in a row is a bad thing, but this class is not constructed
* by end users and is too fine-grained for a builder.
*/
public CacheStats(long hitCount, long missCount, long loadSuccessCount,
long loadExceptionCount, long totalLoadTime, long evictionCount) {
checkArgument(hitCount >= 0);
checkArgument(missCount >= 0);
checkArgument(loadSuccessCount >= 0);
checkArgument(loadExceptionCount >= 0);
checkArgument(totalLoadTime >= 0);
checkArgument(evictionCount >= 0);
this.hitCount = hitCount;
this.missCount = missCount;
this.loadSuccessCount = loadSuccessCount;
this.loadExceptionCount = loadExceptionCount;
this.totalLoadTime = totalLoadTime;
this.evictionCount = evictionCount;
}
/**
* Returns the number of times {@link Cache} lookup methods have returned either a cached or
* uncached value. This is defined as {@code hitCount + missCount}.
*/
public long requestCount() {
return hitCount + missCount;
}
/**
* Returns the number of times {@link Cache} lookup methods have returned a cached value.
*/
public long hitCount() {
return hitCount;
}
/**
* Returns the ratio of cache requests which were hits. This is defined as
* {@code hitCount / requestCount}, or {@code 1.0} when {@code requestCount == 0}.
* Note that {@code hitRate + missRate =~ 1.0}.
*/
public double hitRate() {
long requestCount = requestCount();
return (requestCount == 0) ? 1.0 : (double) hitCount / requestCount;
}
/**
* Returns the number of times {@link Cache} lookup methods have returned an uncached (newly
* loaded) value, or null. Multiple concurrent calls to {@link Cache} lookup methods on an absent
* value can result in multiple misses, all returning the results of a single cache load
* operation.
*/
public long missCount() {
return missCount;
}
/**
* Returns the ratio of cache requests which were misses. This is defined as
* {@code missCount / requestCount}, or {@code 0.0} when {@code requestCount == 0}.
* Note that {@code hitRate + missRate =~ 1.0}. Cache misses include all requests which
* weren't cache hits, including requests which resulted in either successful or failed loading
* attempts, and requests which waited for other threads to finish loading. It is thus the case
* that {@code missCount >= loadSuccessCount + loadExceptionCount}. Multiple
* concurrent misses for the same key will result in a single load operation.
*/
public double missRate() {
long requestCount = requestCount();
return (requestCount == 0) ? 0.0 : (double) missCount / requestCount;
}
/**
* Returns the total number of times that {@link Cache} lookup methods attempted to load new
* values. This includes both successful load operations, as well as those that threw
* exceptions. This is defined as {@code loadSuccessCount + loadExceptionCount}.
*/
public long loadCount() {
return loadSuccessCount + loadExceptionCount;
}
/**
* Returns the number of times {@link Cache} lookup methods have successfully loaded a new value.
* This is always incremented in conjunction with {@link #missCount}, though {@code missCount}
* is also incremented when an exception is encountered during cache loading (see
* {@link #loadExceptionCount}). Multiple concurrent misses for the same key will result in a
* single load operation.
*/
public long loadSuccessCount() {
return loadSuccessCount;
}
/**
* Returns the number of times {@link Cache} lookup methods threw an exception while loading a
* new value. This is always incremented in conjunction with {@code missCount}, though
* {@code missCount} is also incremented when cache loading completes successfully (see
* {@link #loadSuccessCount}). Multiple concurrent misses for the same key will result in a
* single load operation.
*/
public long loadExceptionCount() {
return loadExceptionCount;
}
/**
* Returns the ratio of cache loading attempts which threw exceptions. This is defined as
* {@code loadExceptionCount / (loadSuccessCount + loadExceptionCount)}, or
* {@code 0.0} when {@code loadSuccessCount + loadExceptionCount == 0}.
*/
public double loadExceptionRate() {
long totalLoadCount = loadSuccessCount + loadExceptionCount;
return (totalLoadCount == 0)
? 0.0
: (double) loadExceptionCount / totalLoadCount;
}
/**
* Returns the total number of nanoseconds the cache has spent loading new values. This can be
* used to calculate the miss penalty. This value is increased every time
* {@code loadSuccessCount} or {@code loadExceptionCount} is incremented.
*/
public long totalLoadTime() {
return totalLoadTime;
}
/**
* Returns the average time spent loading new values. This is defined as
* {@code totalLoadTime / (loadSuccessCount + loadExceptionCount)}.
*/
public double averageLoadPenalty() {
long totalLoadCount = loadSuccessCount + loadExceptionCount;
return (totalLoadCount == 0)
? 0.0
: (double) totalLoadTime / totalLoadCount;
}
/**
* Returns the number of times an entry has been evicted. This count does not include manual
* {@linkplain Cache#invalidate invalidations}.
*/
public long evictionCount() {
return evictionCount;
}
/**
* Returns a new {@code CacheStats} representing the difference between this {@code CacheStats}
* and {@code other}. Negative values, which aren't supported by {@code CacheStats} will be
* rounded up to zero.
*/
public CacheStats minus(CacheStats other) {
return new CacheStats(
Math.max(0, hitCount - other.hitCount),
Math.max(0, missCount - other.missCount),
Math.max(0, loadSuccessCount - other.loadSuccessCount),
Math.max(0, loadExceptionCount - other.loadExceptionCount),
Math.max(0, totalLoadTime - other.totalLoadTime),
Math.max(0, evictionCount - other.evictionCount));
}
/**
* Returns a new {@code CacheStats} representing the sum of this {@code CacheStats}
* and {@code other}.
*
* @since 11.0
*/
public CacheStats plus(CacheStats other) {
return new CacheStats(
hitCount + other.hitCount,
missCount + other.missCount,
loadSuccessCount + other.loadSuccessCount,
loadExceptionCount + other.loadExceptionCount,
totalLoadTime + other.totalLoadTime,
evictionCount + other.evictionCount);
}
@Override
public int hashCode() {
return Objects.hashCode(hitCount, missCount, loadSuccessCount, loadExceptionCount,
totalLoadTime, evictionCount);
}
@Override
public boolean equals(@Nullable Object object) {
if (object instanceof CacheStats) {
CacheStats other = (CacheStats) object;
return hitCount == other.hitCount
&& missCount == other.missCount
&& loadSuccessCount == other.loadSuccessCount
&& loadExceptionCount == other.loadExceptionCount
&& totalLoadTime == other.totalLoadTime
&& evictionCount == other.evictionCount;
}
return false;
}
@Override
public String toString() {
return MoreObjects.toStringHelper(this)
.add("hitCount", hitCount)
.add("missCount", missCount)
.add("loadSuccessCount", loadSuccessCount)
.add("loadExceptionCount", loadExceptionCount)
.add("totalLoadTime", totalLoadTime)
.add("evictionCount", evictionCount)
.toString();
}
}